Seediscussions,stats,andauthorprofilesforthispublicationat:http://www.researchgate.net/publication/270914681
Depositionpressureeffectonchemical,
morphologicalandopticalpropertiesofbinary
Al-nitrides
ARTICLEinOPTICS&LASERTECHNOLOGY·JUNE2015
ImpactFactor:1.65·DOI:10.1016/j.optlastec.2014.12.009
CITATION
READS
1
85
5AUTHORS,INCLUDING:
JaimeANDRESPerezTaborda
JulioCaicedo
SpanishNationalResearchCouncil
UniversidaddelValle(Colombia)
27PUBLICATIONS20CITATIONS
86PUBLICATIONS328CITATIONS
SEEPROFILE
SEEPROFILE
W.Saldarriaga
HenryRiascos
NationalUniversityofColombia
UniversidadTecnológicadePereira
44PUBLICATIONS185CITATIONS
47PUBLICATIONS107CITATIONS
SEEPROFILE
Allin-textreferencesunderlinedinbluearelinkedtopublicationsonResearchGate,
lettingyouaccessandreadthemimmediately.
SEEPROFILE
Availablefrom:JaimeANDRESPerezTaborda
Retrievedon:30October2015
Optics & Laser Technology 69 (2015) 92–103
Contents lists available at ScienceDirect
Optics & Laser Technology
journal homepage: www.elsevier.com/locate/optlastec
Deposition pressure effect on chemical, morphological and optical
properties of binary Al-nitrides
Jaime Andrés Pérez Taborda a,b,n, J.C. Caicedo c, M. Grisales d, W. Saldarriaga e, H. Riascos a
a
Universidad Tecnológica de Pereira, Grupo Plasma Láser y Aplicaciones, Colombia
Functional Nanoscale Devices for Energy Recovery Group, Institute of Microelectronics of Madrid, Spain
c
Tribology, Powder Metallurgy and Processing of Solid Recycled Research Group, Universidad del Valle, Cali, Colombia
d
Universidad De la Amazonia, Colombia
e
Laboratorio de Materiales Cerámicos y Vítreos, Universidad Nacional de Colombia, Sede Medellín, A.A. 568, Medellín, Colombia
b
art ic l e i nf o
a b s t r a c t
Article history:
Received 17 August 2014
Received in revised form
3 December 2014
Accepted 8 December 2014
Aluminum nitride films (AlN) were produced by Nd:YAG pulsed laser (PLD), with repetition rate of
10 Hz. The laser interaction on Al target under nitrogen gas atmosphere generates plasma which is
produced at room temperature with variation in the pressure work from 0.39 Pa to 1.5 Pa thus
producing different AlN films. In this sense the dependency of optical properties with the pressure of
deposition was studied. The plasma generated at different pressures was characterized by optical
emission spectroscopy (OES). Additionally ionic and atomic species from the emission spectra obtained
were observed. The plume electronic temperature has been determined by assuming a local thermodynamic equilibrium of the emitting species. Finally the electronic temperature was calculated with
Boltzmann plot from relative intensities of spectral lines. The morphology and composition of the films
were studied using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray
photoelectron spectroscopy analysis (XPS) and Raman Spectroscopy. The optical reflectance spectra
and color coordinates of the films were obtained by optical spectral reflectometry technique in the
range from 400 nm to 900 nm. A clear dependence in morphological properties and optical properties,
as a function of the applied deposition pressure, was found in this work which offers a novel
application in optoelectronic industry.
& 2014 Elsevier Ltd. All rights reserved.
Keywords:
Pulsed laser deposition
Aluminum nitride
Morphology and optical properties
1. Introduction
Aluminum nitride (AlN) thin films are applied widespread because
they have some excellent properties such as chemical stability, high
thermal conductivity, low electric conductivity and wide band gap
(6.2 eV). Moreover, it presents a thermal expansion coefficient similar
to that of GaAs, and a higher acoustic velocity, making it excellent for
optical devices in the ultraviolet spectral region, acoustic optic devices,
and surface acoustic wave (SAW) devices. Polycrystalline films exhibit
piezoelectric properties and can be used for the transduction of both
bulk and surface acoustic waves. Pulsed laser deposition (PLD) growth
of AlN films is rather critical because of its tendency to present microcracking. This tendency is more evident with increasing the thickness
of the film and when using silicon substrates, particularly in the (100)
orientation, while using silicon substrates has been shown to improve
n
Corresponding author. Present address: Instituto de Microelectrónica de Madrid
(IMM-CSIC), Calle de Isaac Newton 8, Tres Cantos, 28760 Madrid, Spain.
E-mail address: jaimeandres@ingenieros.com (J.A. Pérez Taborda).
http://dx.doi.org/10.1016/j.optlastec.2014.12.009
0030-3992/& 2014 Elsevier Ltd. All rights reserved.
the films' growth. Pulsed laser deposition (PLD) using nanosecond
pulses is considered to be one of the most promising techniques for
the synthesis and deposition of thin films [1–4]. This method has
advantages such as high reproducibility, control of the film growth
rate and stoichiometry and low impurity concentration in the composition of deposited films. On the other hand aluminum nitride (AlN)
exhibits attractive properties such as thermal and chemical stability,
high thermal conductivity, high dielectric permittivity, breakdown
field, high-speed piezoacoustic wave and mechanical hardness [1].
Many authors in the literature have discussed the effect of
growth conditions of AlN thin films deposited by PLD related to
the crystallinity, morphology and optical response [5–8]. Clearly,
the growth characteristics influence the final properties of the
materials in a thin layer, but there is a deficiency in the discussion
of the effect produced by the variation of the pressure tank to the
variation in color purity layered AlN obtained by PLD.
The study of pulsed laser ablation plumes has increased the
attention recently due to its importance in laser deposition. The
plasma state is often called the fourth state of matter and transient
phenomenon in nature with characteristic parameters dependent
J.A. Pérez Taborda et al. / Optics & Laser Technology 69 (2015) 92–103
on the rapidly evolving component species. These parameters are
highly dependent on the irradiation conditions, laser intensity,
pulse duration, wavelength, composition and atmosphere. Taking
into account that the relationship between plasma and morphological quality in the films is very important, in this sense the AlN
films are used as substrates for SAW sensors where the surface
quality is a decisive factor in the sensors performance [9,10].
So, the goal of this work is to study the effect of the applied
deposition pressure on the chemical, morphological properties
and optical properties of binary AlN films deposited by PLD on Si
(100) for use in optical and electronic applications. Here, using
nitrogen as working gas, results on AlN films deposited from Al
targets, their characterization by X-ray photoelectron spectroscopy
(XPS), Raman Spectroscopy and scanning electron microscopy
(SEM) as well as investigations associated to changes in optical
response such as reflectance and color purity as function of
pressure deposition values were reported.
2. Experimental
In this research the experiments were carried out in usual PLD
configuration consisting of a laser system into the multiport
stainless steel vacuum chamber equipped with a gas inlet, a
rotating target and a heated substrate holder. The Nd:YAG laser
that provides pulses at the wavelength of 1064 nm with 9 ns pulse
duration and a repetition rate of 10 Hz was used. The laser beam
was focused with an f ¼23 cm glass lens on the target at the angle
of 451, with respect to the normal. The target was rotated to
2.2 rpm to avoid fast drilling. The distance between the target and
the substrate was 6.5 cm. The vacuum chamber was evacuated
down to 10 6 Pa before deposition by using a turbo-molecular
pump backed with a rotary pump. The AlN thin films were
deposited in nitrogen atmosphere as working gas, in an atmosphere of nitrogen reactive, the nitrogen gas pressure varied
between 0.39 Pa and 1.5 Pa and aluminum target (99.99%). The
films were deposited with a laser fluence of 7 J/cm2 for 15 min on
silicon (100) substrates. So, the plasma characterization was
performed by optical emission spectroscopy (OES) by using a
spectrometer model Jobin Yvon Triax 550 of 0.55 m, f ¼6.4
equipped with two gratings of 1200 l/mm and 150 l/mm, coupled
to a CCD camera model 3000 air-cooled multi-channel and
512 512 pixels. The crystal structure of the coating was determined by using a D8 Advance Bruker X-ray diffractometer with
Cu-Ka (λ ¼1.5405 Å) radiation. For the surface study a scanning
electron microscope Philips XL 30 was used . The AlN layers
thickness around 150 nm was determined by the design of a step
between the substrate and the film. A profiler was used to perform
continuous scanning surface that takes into account the film and
the substrate area. A Dektak 8000 profilometer device with a tip
diameter of 12 70.04 μm, scan length range (X) of 5070.1 μm–
200 70.1 mm, scan height range (Y) from 100 71 nm to
1000 70.1 μm, measurement range 50 A–2.520 kA, vertical resolution (max.) of 1 A, sample thickness (max.) of 63.5 mm, horizontal resolution of 0.0033 um, stylus force from 1 to 100 mg and
sample stage theta rotation of 3601 was used.
Chemical composition analysis of the coatings was done with a
Philips XL 30 FEG scanning electron microscope, an X-ray detector
and secondary electrons detector of Lithium Beryllium inside the
chamber with the purpose of amplifying the signal in the EDS
analysis. Moreover, the XPS also was used on AlN samples to
determine the chemical composition and the bonding of aluminum and nitrogen atoms using ESCA-PHI 5500 monochromatic AlKα radiation and a passing energy of 0.1 eV. The surface sensitivity
of this technique is so high that any contamination can produce
deviations from the real chemical composition; therefore, the XPS
93
analysis is typically performed under ultra-high vacuum conditions with a sputter cleaning source to remove any undesired
contaminants. Morphological characteristics of the coatings like
grain size and roughness were obtained using an atomic force
microscope (AFM) from Asylum Research MFP-3Dr and calculated
by a scanning probe image processor (SPIP) which is the standard
program for processing and presenting AFM data, therefore, this
software has become the de-facto standard for image processing in
nanoscale. The Al–N bond was verified by infrared spectroscopy
and Raman and Fourier transform infrared spectroscopy (FTIR)
characteristics of Al–N vibrational modes were found. Optical
reflectance spectra and color coordinates of the samples were
obtained by spectral reflectometry in the range of 400–900 nm by
means of an Ocean Optics 2000 spectrophotometer. The coated
samples received the white light from a halogen lamp illuminator
through a bundle of six optical fibers, and the light reflected on the
samples was collected by a single optical fiber and analyzed in the
spectrophotometer. The fiber was fixed in perpendicular direction
to the sample surface. An aluminum deposited by rapid thermal
evaporation in high vacuum was used as the reference sample, and
the experimental spectra were normalized to 100% reflectance of
the reference sample. The morphology on AlN surface films was
analyzed by SEM (Leika 360 Cambridge Instruments).
3. Results and discussion
3.1. Optical emission for the AlN plume
For the plasma generated by AlN materials a large number of
emission lines attributed to emission bands of aluminum nitride
was identified. In Fig. 1a, the most intense lines are emission of
aluminum species, apparently the main species emitted in the
ablation of aluminum species, being once ionized aluminum (Al II).
The strongest lines in the spectrum of XII in plasma are at
631.337 nm, for electron configuration 1s3p–1s3d. Atomic spectral
lines are also indicating the presence of Al and atomic N2 (Fig. 1b
and c). The oxygen presence was observed in optical emission for
the AlN with 0.53 Pa and 0.66 Pa, which is a product of contamination in the vacuum chamber. All atomic emission lines were
identified through the database of the National Institute of
Standards and Technology-NIST. Also emission lines of nitrogen
species (neutral and multiply ionized) with most intense peaks at
618.909 nm (N I), 644.902 nm (N III), 740.359 nm (N III) were
observed. The emission peak of atomic nitrogen was dominant
compared to the emission peaks of atomic aluminum.
The oxygen presence is also attributed to low flow of nitrogen
gas during the degassing processes. The oxygen species observed
are O II (762.882 nm), O III (751.325 nm) and O V (676.585 nm and
743.153 nm). Shown in 509.985 nm an emission band of AlN (0.0)
[11] is observed. A second emission band, weaker, is analyzed at
523.060 nm for AlN (1.0) [8]. In this work the oxygen bands only
are evidenced for a working pressure of 0.53 Pa. Moreover, in
this work participle density in Debye sphere Nd ¼2.46 10 1 m
was found.
3.2. Local thermodynamic equilibrium for AlN films
In the local thermodynamic equilibrium for AlN it is possible to
take into account that the plume is in local thermodynamic
equilibrium (LTE) [12], therefore, the emission line intensity (I)
in a specific wavelength (λm) may be expressed by
Ln
I mn λmn
Amn g mn
¼ Ln
N
Emn
Z
κT e
ð1Þ
94
J.A. Pérez Taborda et al. / Optics & Laser Technology 69 (2015) 92–103
Fig. 1. Optical emission for the AlN plume with different values of nitrogen pressure: (a) emissivity for N2 1st positive system between 600 nm and 800 nm in AlN films as
function of deposition pressure, (b) optical emission for the AlN with 0.53 Pa, and (c) optical emission for the AlN with 0. 66 Pa.
where λmn is the transition wavelength, Imn is the intensity line
transition observed, Amn is the transition probability, gmn is the
degeneracy of the upper level, N is the total density of the exited
state, Z is the partition function, Emn is the energy of the emitting level, k is the Boltzmann constant and Te is the electronic
temperature. A typical plot is reported in Fig. 2 for the emission of
the AlN plume. The higher temperature calculated in the presence
of N2 under 0.53 Pa can be associated to recombination phenomena which occurs during plume expansion and the thin films
deposition, in relation to local thermodynamic equilibrium of the
electron density, as shown in the following equation [12]:
3
3
ne Z 1:4 1014 T 12
e ðΔE mn Þ cm
ð2Þ
where ne is the electron density, Te is the electronic temperature,
ΔEmn is the transition from the upper energy level (Em) to the
lower energy level (En).
In this paper a value of 5.90 1013 cm 1 was reported for the
LTE approximation, which agrees with the literature [11–13].
On the other hand nitrogen elements are characteristic for the
first and second positive system that occur between 250 nm and
400 nm; although doing different variations in the spectra, such as
integration time and the width of the entrance slit, no prominent
lines were observed in this range. The relaxation of the excited
state of nitrogen in the plasma emission is given by transitions
between atomic energy levels or through state transitions of the
ionized molecule and not by transitions of the neutral molecule.
This suggests that the relaxation process is the recombination of
unpaired electrons with the ionized molecules (Fig. 2b).
3.3. Chemical composition
3.3.1. EDS analysis in AlN films
The EDS results from the AlN films surface showed the
presence of (Al, N, O) element, which is characteristic of those
materials. The areas of the peaks were used to calculate the
composition of both coatings; thus, the values from Fig. 3 indicated that AlN films were substoichiometrics. On the other hand, a
careful correction has to be done in all stoichiometric analyses
because EDS has low reliability for nitrogen concentration. In this
sense, EDS elemental concentrations were obtained using the ZAF
correction method; because certain factors related to the sample
composition, called matrix effects associated with (atomic number
(Z), absorption (A) and fluorescence (F)), can affect the X-ray
spectrum produced during the analysis of electron microprobe
J.A. Pérez Taborda et al. / Optics & Laser Technology 69 (2015) 92–103
-14
Intensity (a.u.)
ln ( I λ / g A )
-16
-18
-20
-22
-24
5.6x10
4
4.9x10
4
4.2x10
4
3.5x10
4
2.8x10
4
2.1x10
4
1.4x10
4
7.0x10
3
95
0.0
-26
23
24
25
26
27
28
29
30
31
500 502 504 506 508 510 512 514 516 518 520
λ (nm)
Energy (eV)
Fig. 2. Local thermodynamic equilibrium: (a) determination of electronic temperature Te ¼8.832.3 K from AlN plume emission in 0.533 Pa N2 by using the line N II and
(b) the plasma electron density ne calculated from Stark broadening, for N II transition (2s2p2–4p) 3p at the line 504.871 N II, and the ne ¼201 1019 cm 3. The error bars
indicate the standard deviation values of the measurements for all AlN materials films.
65
50
O
N
60
Al concentration (%)
45
55
40
50
35
45
Stoichiometric
Concentration
30
40
35
25
30
20
N concentration (%)
Al
25
20
15
2
4
6
8
10
12
14
16
-1
Deposition Pressure (10 Pa)
Fig. 3. Chemical composition by EDS: (a) energy-dispersive X-ray spectroscopy (EDS) values and SEM surface images of AlN films and (b) correlation between work pressure
in the Al–N plasma and aluminum, nitrogen and oxygen contents for deposited AlN thin films. The error bars indicate the standard deviation values of the measurements for
all AlN systems.
3.3.2. XPS analysis in AlN films
The chemical relation between EDS results and XPS was
explored in the current research. Thus, the survey spectra of
4x10
3x10
Intensity (c/s)
and therefore, these effects should be corrected to ensure the
development of an appropriate analysis.
The correction factors for a standard specimen of known
compositions were determined initially by the ZAF routine. The
relative intensity of the peak K was determined by dead time
corrections and a referent correction for the X-ray measured. So,
before each quantitative analysis of an EDS spectrum for AlN
deposited with 9.3 10 1 Pa, a manual background correction and
an automated ZAF correction was carried out [14]. Thus, Fig. 3a shows
the energy-dispersive X-ray spectroscopy (EDS) values of AlN films
deposited with different work pressures. All samples were observed
via SEM and chemical analyses were done with an amplification of
20,000 . The presence of oxygen has been often found during the
production of AlN, which is normally associated to residual oxygen in
the chamber [11]. Fig. 3b shown the dependence of work pressure on
decrease of Al content; moreover a little increase in the N concentration in relation to the increase of deposition pressure has been
observed. This effect can be associated to high sensitivity of ionic
exchange in nitrogen under pressure changes.
2x10
1x10
4
4
4
4
0
1400 1200 1000 800 600 400
Binding energy (eV)
200
0
Fig. 4. XPS spectrum of Al 2p–N 1s from Al–N film as a function of applied
pressure.
Al 2p, and N 1s in Fig. 4 were recorded from AlN films, as shown
in Fig. 5. From Fig. 5(a), the Al 2p peak is composed of a shoulder
separated by 1.7 eV with intense peak. The XPS spectrum of Al
J.A. Pérez Taborda et al. / Optics & Laser Technology 69 (2015) 92–103
Al2p Centroid ðeVÞ ¼
AAl
2p3=2
EAl
2p3=2
þ AAl 2p1=2 EAl 2p1=2
AAl
2p3=2
þ AAl 2p1=2
areas without O 1s contribution gives an atomic ratio of Al:
N¼ 0.392:0.588, which is similar to the stoichiometry of
Al0.40N0.60 [20] and close to EDS results showed in Fig. 3. So, in
Fig. 6, it is a clear dependence on the concentration of nitrogen
and oxygen in AlN thin films.
3.4. Structural characterization by XRD results
The x-ray diffraction patterns for AlN deposited with
9.3 10 1 Pa observed in Fig. 7 are at 37.91 and 44.291, corresponding to AlN c-axis (0002) and AlN (200) orientations respectively. As it can be observed, strong preferential c-axis orientation
is obtained for the lower nitrogen–aluminum ratio. The crystallographic orientation of the grains in the film is determined by
the preferential growth of certain crystal planes over others. The
mechanism of preferential orientation of AlN films can be
explained by the crystalline lattice structure generated by AlN
configuration materials which is in agreement with optical emission results (Fig. 1), EDS (Fig. 3) and XPS results (Fig. 5). To further
obtain information regarding bond formation and structure the
polycrystalline hexagonal structure of wurtzite type (file no. 251133 of form JCPDS-ICDD diffraction database) was detected in all
65
60
60
55
55
50
50
45
45
40
40
35
35
30
25
30
4
6
8
10
12
14
-1
Fig. 6. Compositions results from XPS analysis showing the pressure dependence
at the concentrations of N and O deposited on Si at 300 1C. Oxygen is the only
observed contamination in these films. The error bars indicate the standard
deviation values of the measurements for all AlN layers.
4
4
1.6x10
N1s
Al2p
Al-O
76.27 eV
4
4
1.5x10
Al-N
73.78 eV
4
1.0x10
Intensity (a.u.)
Intensity (a.u.)
16
Deposition Pressure (10 Pa)
2.5x10
4
70
65
ð3Þ
where A is the sub-peak integrated area and E is the adjusted subpeak binding energy in eV. Therefore, calculation of the peak
2.0x10
75
N
O
70
Composition (at.%)
2p can be fitted well by two Gaussian functions. The value of
binding energies obtained for the Al 2p peak was 73.9 eV and the
higher value for Al 2p was 75.9 eV, respectively. According to the
literature [15–17] for the Al 2p peak, the first one (73.9 eV) and the
second one (75.9 eV) can be assigned to Al–N and Al–O bonds
respectively. The appearance of the peak at 73.9 eV clearly shows
that Al has reacted with N; therefore, it can be assigned to AlN
[16,17]. In Fig. 4 N 1s peak is composed of spin doublets, each
separated by 2.9 eV. The XPS spectrum of N 1s can be fitted well by
two Gaussian functions which depicts the N 1s spectrum with
values at 397.3 eV and 400.2 eV characteristic for N–N and Al–N
bonds, respectively [18,19].
The high resolution X-ray photoelectron spectroscopy (XPS)
results for AlN deposited with 9.3 10 1 Pa demonstrate that Al
atoms bonded to N in the form of nitride, because the elemental
concentration of the Al–N film was obtained by adjusting the laser
incidence on Al target and N2 was the working gas in this research;
it was discovered that amounts of Al–N in the AlN film were
maximum in the current establishment of process conditions and
the ratio of Al to N in the film was about 2:1. Generally, formative
Al–N phase indicates that the aluminum and nitrogen activity and
activation energy provided by the present deposition conditions
are enough for the formation of AlN thin film. Although the surface
temperature of the substrate during deposition of AlN film is
around 300 1C, the substrate lies in a high-density plasma region
and a high ion-to-atom ratio of aluminum and nitrogen can be
propitious to the formation of AlN phase at the low temperature
below 330 1C. All aluminum-nitride films with all Al 2p peaks
were fitted as one or more pairs of spin–orbit split sub-peaks with
a separation of 0.4 eV between the Al 2p3/2 and Al 2p1/2 components (Fig. 5a). The ratio of the area of the 2p3/2 component to the
area of the 2p1/2 component was fixed at 2:1. Moreover all N 1s
peaks were fitted as one or more pairs of spin–orbit split subpeaks with a separation of 0.2 eV, sowing the N–Al bound
centered in 399.66 eV and N–N centered in 402.23 eV (Fig. 5b).
All Al 2p sub-peaks were fitted as 95% Gaussian. For this study,
the binding energy of a fitted Al 2p spin–orbit sub-peak pair is
reported as the centroid of the pair. The centroid of the spin–orbit
pair in eV was calculated as shown
Composition (at.%)
96
1.2x10
N-Al
399.66 eV
3
8.0x10
3
4.0x10
3
5.0x10
N-N
402.23 eV
0.0
0.0
80 79 78 77 76 75 74 73 72 71 70
Binding energy (eV)
406
404
402
400
398
396
394
Binding energy (eV)
Fig. 5. High-resolution XPS spectrum of: (a) Al 2p and (b) N 1s, where the few formation of oxy-nitride N–Al–O and Al–N bonds are observed to occur at different
temperatures.
J.A. Pérez Taborda et al. / Optics & Laser Technology 69 (2015) 92–103
films. Such one axial hexagonal texture with c-axis perpendicular
to the Silicon substrate has been detected in AlN films. As the (103)
planes make a large angle with the (200) ones, the (103) diffraction is competitive to the (0002) one in terms of texture and the
ratio is thus directly related to the contribution of the hexagonal
(0002) texture component.
3.5. Vibrational characterization by FTIR and Raman results
deposited films there is residual stress that induces the shift of
the FTIR peaks from their characteristic positions. It can be due to
the non-equilibrium nature of PLD [20–22].
In this sense the AlN normally crystallize in the hexagonal
wurtzite structure (space group C46v-P63mc) with four atoms in
the unit cell. Then, from Raman results, in Fig. 8b for AlN deposited
with 9.3 10 1 Pa it was possible to observe that the k ¼0 point
group theory predicts the following eight sets of modes: 2A1 þ
2B þ 2E1 þ 2E2 of which one Al, one El, and two E2 are Raman
active. One set of A1 and one of E1 correspond to acoustic phonons.
The B modes are silent [1]. Note that phonons with E1 and E2
symmetry, respectively, are twofold degenerate. The modes with
A1 and E1 symmetry are also infrared active. The frequencies are all
measured with an error of 71 cm 1. Moreover Table 1 shows the
FTIR and Raman active modes associated to Al–N vibrations
[7–10]. The FTIR and Raman spectra are in good agreement with
the optical emission results (Fig. 1), EDS (Fig. 3), XPS results (Fig. 5)
and XRD results (Fig. 7), which confirm the formation of large
hexagonal AlN material films.
Table 1
Vibrational modes reported in the literature for hexagonal aluminum nitride films.
AlN (103)
Si - Substrate
AlN (200)
Intensity (u.a)
AlN (0002)
FTIR spectrometry measurements were carried out for the
same films previously analyzed by XRD. It was reported that
crystalline AlN exhibits characteristic transverse optical (TO) and
longitudinal optical (LO) modes. Fig. 8a shows FTIR spectra of a
spectrum for AlN deposited with 9.3 10 1 Pa in the range of
468–800 cm 1; after deconvolution the respective modes are
active in the infrared observed, especially a narrow band centered
at 680 cm 1 which may be attributed to the contribution of the
phonon mode E1 (TO) of the w-AlN as well as the presence of five
bands around 485 cm 1, 520 cm 1, 615 cm 1, 655 cm 1 and
691 cm 1, associated with Al–O bonds characteristic of a symmetric stretching, Al–N non-stoichiometric phases (AlxNy), the
phonon mode A1 (TO) of hexagonal AlN, the LO phonon mode of
AlN hexagonal and hexagonal Al–N, respectively. Inside the
P = 0.93 Pa
30
35
40
45
50
55
2θ (Degrees)
60
65
97
Mode symmetry
Frequency (cm 1)
Reference
E2
665
303
426
[7]
[10]
[10]
A1 (TO)
667
659
[7]
[8–9]
E1 (TO)
667
672
671
614
[7]
[8]
[9]
[10]
A1 (LO)
910
897
888
663
[7]
[8]
[9]
[10]
E1 (LO)
910
912
895
821
[7]
[8]
[9]
[10]
70
Fig. 7. XRD results showing the polycrystalline hexagonal structure of AlN wurtzite
(file no. 25-1133 of form JCPDS-ICDD diffraction database) deposited on Si (100)
substrates at 300 1C and a pressure of 0.93 Pa nitrogen.
96
Raman Intensity
Transmittance (%)
100
92
88
84
480
560
640
720
Wavenumber (Cm-1)
800
600
650
700
750
800
850
900
Wavenumber (Cm-1)
Fig. 8. Vibrational analysis for AlN materials films: (a) FTIR spectroscopy of AlN films deposited on Si (100) substrates at 300 1C and a pressure of 0.93 Pa nitrogen with E2
(high) phonon mode and (b) Raman shift measures of AlN films deposited with 9.3 10 1 Pa where it was possible to observe that the k ¼ 0 point group theory predicts the
following eight sets of modes.
98
J.A. Pérez Taborda et al. / Optics & Laser Technology 69 (2015) 92–103
3.6. Surface topography and morphological results analyzed by AFM
and SEM
The observed dependence of the AlN films surface morphology
under nitrogen pressure during deposition is closely related with
the film growth mechanism, associated to the surface diffusion
length (L) which is given by [20]
L ðDτÞ1=2
ð4Þ
where D is the diffusion coefficient and τ is the residence time of
adatoms. Larger values of diffusion length imply more time for the
adatoms to find energetically favorable lattice positions, thus,
reducing the density of surface defects and improving the crystal
quality.
Associating Eq. (4), Table 1 and Fig. 9 it is possible to show the
surface morphology of AlN films. Therefore, the changes on
morphological surface as functions of increase in the deposition
pressures were studied by recording AFM images along with SEM
micrographs. These results evidence the random distribution of
micro-particles or micro-droplets on these surfaces as a function
of deposition pressure (0.66 Pa and 0.53 Pa). Thus, the deposition
pressure affects clearly the increase of grain size, roughness and
micro-drops; this can be possible due to low surface mobility
when the pressure was varied from 0.39 Pa to 1.5 Pa. This surface
mobility reduces the possibility that the micro-drops are anchored
on the surface when arriving with high energy on AlN film. Other
possible reason can be associated with the mean free path that
produces surface diffusion of nano-drops or micro-drops which
can decrease the overall number of particles, also affecting the
boundaries sizes. In this sense it was presented in Table 2 the
surface roughness, grain size for AlN films grown at 0.39 and
0.53 Pa, and their optical emission lines due to optical emission
spectrometry signals from AlN plasma.
3.7. Optical reflectance analysis of AlN films
The reflectivity measure is the fractional amplitude of the
reflected electromagnetic field, while reflectance refers to the
fraction of incident electromagnetic power that is reflected at an
interface. The reflectance is thus the square of the magnitude of
the reflectivity. The reflectivity can be expressed as a complex
number as determined by Fresnel's equations for a single layer,
whereas the reflectance is always a positive real number. In certain
fields, reflectivity is distinguished from reflectance by the fact that
reflectivity is a value that applies to thick reflecting objects. When
reflection occurs from thin layers of material, internal reflection
effects can cause the reflectance to vary with surface thickness.
Reflectivity is the limit value of reflectance as the surface becomes
thick; it is the intrinsic reflectance of the surface, hence irrespective of other parameters such as the reflectance of the rear surface.
On the other hand, the dominant wavelength of a color stimulus is
defined as the wavelength of the monochromatic stimulus that,
when additively mixed in suitable proportions with the specified
achromatic stimulus, matches the color stimulus considered [21].
Taking into account the above, an example in thin film
calculator in OptiScan is given to calculate the reflectance and
transmittance of Krestchmann configuration which generate surface plasma resonance at a certain incident angle. Unfortunately
the other properties of the surfaces, such as reflectance, transmittance, or phase change, are rarely satisfied. However the thin films
are commonly used to modify these properties without altering
the specular behavior. In an optical coating, the films, together
with their support, or substrate, are generally solid [22]. The
particular materials used for the AlN films vary with the applications. It is possible to construct assemblies of thin films which will
reduce the reflectance of a surface and hence increase the
transmittance of a component, or increase the reflectance of a
surface, or which will give high reflectance and low transmittance
over part of a region and low reflectance and high transmittance
over the remainder and so on. In this sense in the current work for
AlN films the reflectance, R was taken as the ratio of the irradiance
of the reflected beam to that of the incident beam, and transmittance, T, as the ratio of the irradiance of the transmitted beam to
that of the incident beam, and defined as follows [22,23]:
η Y
η Y n
4η0 ReðYÞ
R¼ 0
U 0
; T¼
ð5Þ
η0 þ Y
η0 þ Y
ðη0 þ YÞ U ðη0 þ YÞn
where R is the reflectance, T is the transmittance, η0 is the surface
admittance for incident medium, and Y is the surface admittance
of the thin films and substrate; moreover the effects of multiple
films are included in the surface admittance. Each layer generates
a matrix in the equation which will change the electric and
magnetic fields [22,23].
Table 2
Surface roughness, grain size for AlN films grown at 0.39 and 0.53 Pa, and their
optical emission lines due to optical emission spectrometry signals from AlN
plasma.
Pressure
(Pa)
Roughness
(nm)
Grain size
(nm)
%At
(Al)
%At
(N2)
OES
0.39
3.8
85.2
26.30
50.85
0.53
3.6
62.9
23.70
58.80
Al XII—N III—O V AlN
(0.0) AlN (1.0)
Al XII—N II—O III
Fig. 9. Deposition conditions as functions of morphological properties: (a) Relationship among surface roughness, grain size with plasma pressure and (b) SEM micrograph
and AM images for AlN thin films deposited with a pressure of 0.66 Pa and 0.53 Pa.
J.A. Pérez Taborda et al. / Optics & Laser Technology 69 (2015) 92–103
In this work the AlN films have been compared with pure
aluminum because the aluminum mirror finish has the highest
reflectance of any metal in the 200–500 nm range and the 3000–
10,000 nm range (far IR) regions, while in the 500–700 nm visible
range it is slightly outdone by AlN and silver, but in the 700–
3000 nm range (near IR) it is slightly outdone by gold and copper
materials [24]. Fig. 10 shows the optical reflectance spectra of the
AlN single layers obtained at different deposition pressures. The
reflectance of the aluminum and the eye sensibility are shown for
comparison. The spectra of the samples show high reflectance for
long wavelengths, near to 62% for the AlN films deposited with
4 10 1 Pa and close to 28% for AlN films deposited with 1.5 Pa.
These values of reflectances at these wavenumbers agree well with
previous reports in the literature for AlN films [25,26]. However in
this work it was observed that the minimum of reflectance at
550 nm is due to interference effect in reflected light.
However a clear decrease in reflectivity for short wavelengths
is seen, characteristic of a system with high free electron density
with a reflectance edge below 530 nm due to a screened plasma
resonance [27]. The white and aluminum colors of the AlN films
are a result of the steep plasma reflection edge that occurs in the
visible region where the reflectivity minimum is around 540 nm.
The reflectance values for AlN films are in good agreement with
the optical emission results (Fig. 1), EDS (Fig. 3), XPS results
(Fig. 5), XRD results (Fig. 7), FTIR-Raman spectra (Fig. 8), and
AFM-SEM results (Fig. 9). The reflectance values for AlN films are
in good agreement with the optical emission results (Fig. 1) by the
spectral signals Al XII (631.337 nm) and NI (618.909 nm), characteristics of AlN, EDS (Fig. 3) with XPS (Fig. 5) results because of the
AlN adjusted stoichiometry strapped with bounds from Al 2p and
N 1s spectral signals (Al–N 73.78 eV), XRD results (Fig. 7) associated with polycrystalline hexagonal structure of wurtzite type
(0002) adjusted to high reflectance, FTIR-Raman spectra (Fig. 8)
due to vibrational signals typical of AlN with suitable optical
whining (Al–N E1(TO) 678.8 cm 1 and Al–N A1(TO) 692.5 cm 1),
and AFM-SEM results (Fig. 9) associated with superficial morphology and adjusted to the other physical and chemical characteristics
discussed above absorbs and disperses spectral lines of light
incident at the rank of major optical reflectance [28].
Moreover in this research high dependency on reflectance
percentages in this work was found when the deposition pressure
was varied from 0.39 Pa to 1.5 Pa, therefore, the changes in optical
properties can be related not only with changes on temperature
deposition but also with changes generated on morphology surface films due to variation of deposition pressure (Fig. 11a). Fig. 11a
exhibits one constant region for wavelength of 760–800 nm; in
those regions it is possible to appreciate the effect of the deposition pressure on reflectance of the films. Fig. 11b shows the
decrease of reflectance when the deposition pressure is increased,
which indicates that pressure also promotes the absorbance in the
AlN deposited via PLD.
Moreover the error bars of the values presented in Fig. 10 were
obtained at the base of the uncertainty in adjusting of reflectance
curves as a function of wavelength, to assign values to the
parameters determined by fitting (reflectance or transmittance
for AlN films). Therefore, the reflectance values shown in Fig. 11b
(filled triangles) are the average of data obtained in each run and
thus have their respective error bars. In this sense the error bars
indicate the standard deviation values of the measurements for all
AlN films [28].
From the reflectance spectra a weak but clear effect of deposition pressure on the optical properties is seen. As the pressure is
decreased, the reflectance of the films tends to be higher in the
near infrared region, while the minimum in reflectance, between
562 nm and 571 nm for all AlN films.
100
90
Reflectance (%)
80
70
60
50
40
30
20
10
0
400
500
600
700
Wavelengeth (nm)
800
99
900
Fig. 10. Dominant wavelength and color purity results: (a) Optical reflectance
of AlN films deposited onto Si (100) substrates at different deposition pressures
(0.39–1.5 Pa); aluminum optical reflectance and eye sensibility were also plotted as
references.
70
70
65
65
60
Reflectance (%)
Reflectance (%)
60
55
50
45
40
35
30
55
50
45
40
35
30
25
20
760 765 770 775 780 785 790 795 800
Wavelength (nm)
25
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Deposition pressure (Pa)
Fig. 11. Reflectance dependency: (a) Reflectance of AlN films deposited onto Si (100) substrates at different deposition pressures of 760–800 nm wavelength and
(b) reflectance as function of deposition pressure. The error bars indicate the standard deviation values of the measurements for all AlN films.
100
J.A. Pérez Taborda et al. / Optics & Laser Technology 69 (2015) 92–103
0.9
Table 3
Optical characteristics for AlN films deposited at 300 1C onto Si substrate.
0.8
0.7
Y Axis
0.6
0.5
Deposition pressure
(Pa)
Dominant wavelength
(nm)
Color
purity
Axis X Axis Y
4.0 10 1
5.3 10 1
9.3 10 1
1.5
Reference aluminum
571
570
567
562
574
0.71
0.66
0.63
0.62
0.90
0.3329
0.343
0.242
0.210
0.358
0.341
0.362
0.123
0.119
0.371
0.4
Dominant wavelength and color purity have been determined
from the reflectance spectra of all films. The color purity changes
with the deposition pressure, in this study ranges from 0.39 Pa to
1.5 Pa for AlN films, away from the color purity of pure aluminum
(0.90), confirming that the films are less white compared with the
aluminum. So, the results of color measurement indicate that all
films reflect a hue slightly shifted far to the white as compared to
aluminum reflectivity and with similar color purity (Table 3). The
dominant wavelength was varied for all the samples, from 562 nm
to 570 nm. AlN films deposited with lower pressure are situated
little close to that of pure aluminum reference (574 nm).
0.3
0.2
0.1
0.0
0.0
0.1
0.2
0.3 0.4
X Axis
0.5
0.6
0.7
Fig. 12. Chromatic diagram, in the x, y coordinates, of the reflectivity for AlN films.
White coordinates of achromatic point are located at (1/3, 1/3).
3.8. Dominant wavelength and color purity analysis of AlN films
3.8.1. Dominant wavelength
In order to calculate dominant wavelength for AlN films, it was
necessary first introduce the identification of a color by its “x–y
chromaticity coordinates” as plotted in the Chromaticity Diagram
(Fig. 12). The diagram enables to quantitatively graph the hue and
saturation of a particular color by its dominant wavelength and
excitation purity, respectively [29].
The first step in calculating the chromaticity coordinates is to
compute the “tristimulus values” of a particular filter with a
particular illumination for AlN films. Loosely, the tristimulus
values can be thought of as the amount of red, green, and blue
in the filter, but the correspondence is not quite that simple. These
values are based on the empirically determined CIE Color Matching Functions X (λ), Y(λ), and Z (λ) [29]. Note that we typically
use the CIE 1931 2-degree field-of-view standard, as this one is the
most well-known and widely used. It is useful to note that by
definition the y (λ) Color Matching Function is identical to the
Photopic Curve V(λ), or y (λ) V(λ). The Color Matching Functions can also be obtained from numerous sources presented in
the literature [29,30]. In this sense the tristimulus values X, Y, and
Z are then given by
Z 1
X¼
IðλÞTðλÞχ ðλÞdλ
ð6Þ
0
Z
Y¼
0
Z
Z¼
1
1
0
IðλÞTðλÞyðλÞdλ
IðλÞTðλÞzðλÞdλ
ð7Þ
ð8Þ
For determination of dominant wavelength in AlN films (Table 3),
one simply constructs a line between the chromaticity coordinates of
the reference white point on the diagram (for instance, CIE-E, CIEC,
etc.) and the chromaticity coordinates of the filter and then extrapolates the line from the end that terminates at the filter point. The
wavelength associated with the point on the horseshoe-shaped curve
at which the extrapolated line intersects is the dominant wavelength
[30].
3.8.2. Color purity
Once the line is constructed to determine the dominant
wavelength, it is very straightforward to calculate the excitation
purity (color purity) of a color that represents the filter transmission. The excitation purity applied for AlN films is defined to be the
ratio of the length of the line segment that connects the chromaticity coordinates of the reference white point and the color of
interest to the length of the line segment that connects the
reference white point to the dominant wavelength [31]. These
line segments are illustrated in Fig. 12. As pointed out above, the
excitation purity is a well-defined quantitative measure of the
saturation of a particular color. The larger the excitation purity, the
more saturated the color appears, or the more similar the color is
to its spectrally pure color at the dominant wavelength. The
smaller the excitation purity, the less saturated the color appears,
or the more white it is. Pastel colors are very poorly saturated, for
example. When there is no well-defined dominant wavelength,
the excitation purity is still defined as described above, except that
the denominator should be taken as the length of the line segment
between the reference white point and the point at which the
dominant wavelength construction line intersects the line that
contains the purple colors near the bottom of the diagram. For
every wavelength in the spectrum (e.g. AlN films), is possible to
calculate (X,Y,Z) from CIE color matching functions. Therefore the
Plot (x,y) for all wavelengths in the spectrum generates a horseshoe shaped diagram thus, all physical colors lie inside the horseshoe. Finally the color, as determined from the tristimulus values,
can now be represented graphically on a two-dimensional graph
called the Chromaticity Diagram with x–y coordinates on this
graph which are given by [31–33]
χ¼
X
Y
; y¼
X þY þZ
X þY þZ
ð9Þ
Taking into account the last discussion, the excitation purity
(purity for short or color purity) of a stimulus is the difference
from the illuminant's white point to the furthest point on the
chromaticity diagram with the same hue (dominant wavelength
for monochromatic sources); using the CIE 1931 color space given
by [31]
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ðx xn Þ2 þ ðy yn Þ2
pe ¼
ð10Þ
ðx1 xn Þ2 þ ðy1 yn Þ2
101
0.74
Aluminum 574 (nm)
572
0.72
570
0.70
Color purity
Dominant wavelength (nm)
J.A. Pérez Taborda et al. / Optics & Laser Technology 69 (2015) 92–103
568
566
564
0.66
0.64
0.62
562
560
0.68
AlN 300 °C
Aluminium (0.90)
0.4
0.6
0.8
1.0
1.2
1.4
0.60 Aluminium (0.90)
0.4
1.6
0.6
0.8
AlN 300 °C
1.0
1.2
1.4
1.6
Deposition pressure (Pa)
Deposition pressure (Pa)
Fig. 13. Color results for AlN films deposited with 0.93 Pa: (a) dominant wavelength as function of deposition pressure and (b) color purity as a function of deposition
pressure. The error bars indicate the standard deviation values of the measurements for all AlN films.
where (xn, yn) is the chromaticity of the white point and (xI, yI) is the
point on the perimeter whose line segment to the white point
contains the chromaticity of the stimulus. Different color spaces, such
as CIELAB or CIELUV may be used, and will yield different results.
Taking into account the last discussion in the Fig. 13a are
observed the differences in the dominant wavelength for all AlN
films deposited with different deposition pressures. In Fig. 13b the
influence of deposition pressure on color purity can be observed.
This graph shows the increase of purity values towards color gray
purity. The wavelength is an important optical characteristic for
different materials in relation with the changes observed in AlN
plasma (Figs. 1–3).
Moreover the dominant wavelength and color purity values for
AlN films are in good agreement with the optical emission results
(Fig. 1), EDS (Fig. 3), XPS results (Fig. 5), XRD results (Fig. 7), FTIRRaman spectra (Fig. 8), AFM-SEM results (Fig. 9) and the reflectance values (Figs. 10 and 11) which confirm the susceptibility that
present the AlN films in terms of dominant wavelength and color
with changes in deposition pressure. So, when the wavelength in
the AlN layers is changed it is possible to observe that natural color
is changed. In this sense the purity color dependence and other
optical constant dependence in AlN films with pressure obtained
in this work demonstrate the possibility of some purity color
control. The last discussion can be proved observing the changes
in the optical energy gap, plasma frequency and refractive index as
a function of deposition pressure (Table 4).
In this sense the error bars of the values presented in Fig. 12
were obtained at the base of the uncertainty in adjusting chromatic diagram for different disposition pressures, to assign values
to the parameters determined by fitting (dominant wavelength
and color purity for AlN layers). Therefore, these optical constant
values shown in Fig. 13 (filled, circles and squares) are the average
of data obtained in each run and thus have their respective error
bars. In this sense the error bars indicate the standard deviation
values of the measurements for all AlN films.
3.9. Optical energy gap, plasma frequency and refractive index
3.9.1. Optical energy gap
In crystalline semiconductors, equation (11) has been obtained
to relate the optical energy gap (Egap) with absorption coefficient
from reflectance results given by [34]
αðvÞhv ¼ Bðhv Egap Þ
m
ð11Þ
where Egap is the optical energy gap, B and hυ are the optical gap
constant, and incident photon energy, respectively; α(v) is the
Table 4
Optical constants (energy gap, plasma frequency and refractive index) for all AlN
films as function of deposition pressure.
Deposition
pressures (Pa)
Optical energy
gap (eV)
Plasma frequency
(cm 1)
Real refractive
index
4.0 10 1
5.3 10 1
9.3 10 1
1.5 10 1
6.2
5.9
5.5
5.3
4125
3873
3220
3210
2.194
2.175
2.154
2.149
absorption coefficient defined by Beer–Lambert's law as α(v) ¼
2.302 Abs(λ)/d where d and Abs are the film thickness and film
absorbance, respectively. For more precise determination of α, it is
necessary to perform corrections to the absorption due to reflection; also, m is the index which can have different values of 1/2,
3/2, 2, and 3 [34]. In this sense the optical energy gap as function
of deposition pressures for AlN films has been presented in Table 4.
3.9.2. Plasma frequency
The plasma frequency (ωp) is the most fundamental time-scale
in plasma physics. Clearly, there is a different plasma frequency for
each species. However, the relatively fast electron frequency is, by
far, the most important, and references. So, it is easily seen that ωp
corresponds to the typical electrostatic oscillation frequency of a
given species in response to a small charge separation. For
instance, consider a one-dimensional situation in which a slab
consisting entirely of one charge species is displaced from its
quasi-neutral position by an infinitesimal distance, associated to
higher charge carrier concentration with the higher the plasma
frequency. Therefore, plasmon oscillations for different materials
are excited in different spectral regions. Thus, in many semiconductors like (AlN), the plasma reflection edge can be found in the
reflectance as functions of wavelength. The spectral position of the
plasma reflection edge depends on the charge carrier concentration according to Eq. (12) [35]. Taking into account the above the
plasma frequency (ωp) as a function of deposition pressures for
AlN films [36] has been presented in Table 4
ωp ¼
1=2
1 4π Ne2
2 π c mn ε 1
ð12Þ
where ωp is the plasma frequency, N is the free electron density, e is
the electron charge, mn is the effective mass of electrons, and ε1 is
the high frequency dielectric constant and c is the velocity of light.
102
J.A. Pérez Taborda et al. / Optics & Laser Technology 69 (2015) 92–103
3.9.3. Refractive index
It is known that several widely used methods of analyzing
reflectance (R) and transmittance (T) for a supported thin film
neglect the effect of the rear surface of the substrate. Equations are
given which relate R and T to the complex refractive index (n-ik)
and thickness of the thin film, and a method for their solution has
been described. This relies on Powell's technique, and permits
changes to be made to the equations relating R, T to (n-ik). This
flexibility has allowed the calculation of the effect of the neglect of
the rear of the substrate. An example is given of the use of the
method for the determination of refractive index (n-ik). In this
research aluminum nitride (AlN) with wurtzite phase (w-AlN)
with a wide band gap (6.2 eV) for semiconductor material was
used, giving it potential application for deep ultraviolet optoelectronics. The refractive index for all AlN films is shown in Table 4.
The refraction index has been calculated from relation which holds
for the reflectance measurements [37]
2nd ¼ N λ
ð13Þ
where n is the refraction index, d is the sample thickness, and N is
the interference order. The interference order was determined
graphically. In the region where the refraction index is weakly
dependent on λ (λ 44500 Å) the dependence of N on 1/λ is
practically linear, and in the case of sufficiently thin sample N
may be determined precisely from the intersection of this line
with the y-axis.
4. Conclusions
A dependency in relation to nitrogen concentration, roughness
and grain size in the AlN films with the nitrogen work pressure
was found in this work, increasing in this sense the nitrogen
concentration and the roughness on AlN films. The plasma
pressure affects the stoichiometry and the morphological nature
in the AlN films. The variation of nitrogen work pressure exhibits
low effect on intensity of the spectral lines emitted. The electron
temperature value (Te ¼8832.3 K) presented in the aluminum
nitride plasma is similar to previous works. Structural and compositional results show that the thin films deposited at a temperature of 300 1C improved orientation of hexagonal AlN
increases as the reflectance values for the lower deposition
pressures. X-ray photoelectron spectroscopy (XPS) confirmed the
formation of the binary films AlN.
For AlN films the pressure deposition has a marked influence
on the optical properties. A decrease in the reflectance of 55%, a
reduction of color purity about 13% and decrease in the dominant
wavelength around 1.6% was found with deposition pressure
between 4.0 10 1 Pa and 1.5 Pa. This conclusion can be proved
observing the changes in the optical energy gap, plasma frequency
and refractive index as function of deposition pressure. So, the
purity color dependence in AlN films with pressure obtained in
this work demonstrates the possibility of some purity color
control.
Acknowledgments
J.A. Pérez acknowledges projects: Nano-structured High-efficiency
Thermo-Electric Converters (nanoHITEC) and Photoacoustic Measurements of Nanostructures for Thermoelectric Applications (PHOMENTA) from MINECO and Santander bank and your scholarship
program “Young Professors and Researchers Latin America, Santander Universities” (Spain, 2013)
References
[1] Murakami K. Laser ablation of electronic materials—basic mechanisms and
applications. In: Fogarassy E, Lazare S, editors. Amsterdam: Elsevier; 1992.
p. 125.
[2] Baek J, Ma J, Becker MF, Keto JW, Kovar D. Correlations between optical
properties, microstructure, and processing conditions of AlN thin films
fabricated by PLD. Thin Solid Films 2007;515:7096 (ss-04).
[3] Sudhir GS, Fujii H, Wong WS, Kisielowski C, Newman N, Dieker C, et al. Pulsed
laser deposition of aluminum nitride and gallium nitride thin films. Appl Surf
Sci 1998;471:127–9.
[4] Kaluza N, Steins R, Cho YS, Sofer Z, Hardtdegen H. The effects on surface
morphology and crystal quality of undoped bulk AlN layers, grown on c-plane
sapphire substrates. In: Proceedings of the 11th European workshop MOVPE.
Lausanne, Switzerland. 2005. p. 179–81.
[5] Szekeres A, Fogarassy Zs, Petrik P, Vlaikova E, Cziraki A, Socol G, et al.
Structural characterization of AlN films synthesized by pulsed laser deposition. Appl Surf Sci 2011;257:5370–4.
[6] Ristoscu C, Ducu C, Socol G, Craciunoi F, Mihailesc IN. Structural and optical
characterization of AlN films grown by pulsed laser deposition. Appl Surf Sci
2005;248:411–5.
[7] Bathe R, Vispute RD, Habersat D, Sharma RP, Venkatesan T, Scozzie CJ, et al.
AlN thin films deposited by pulsed laser ablation, sputtering and filtered arc
techniques. Thin Solid Films 2001;398:575–80.
[8] Bakalova S, Szekeres A, Cziraki A, Lungu CP, Grigorescu S, Socol G, et al.
Influence of in-situ nitrogen pressure on crystallization of pulsed laser
deposited AlN films. Appl Surf Sci 2007;253:8215–9.
[9] Bakalova S, Szekeres A, Cziraki A, Huhn G, Havancsak K, Grigorescu S. Surface
morphology studies of AlN films synthesized by pulsed laser deposition.
Vacuum 2009;84:155–7.
[10] Franco LM, Pérez JA, Riascos H. Estudio espectroscópico de plasmas del aire,
cobre y aluminio producidos por láser pulsado. Rev Col Fís 2008;1:176–80.
[11] Pérez JA, Vera LP, Riascos H, Caicedo JC. Optical emission spectroscopy of
aluminum nitride thin films deposited by pulsed laser deposition. J Phys: Conf
Ser 2014;511:12078–83.
[12] Santangata A, Marotta V, Orlando S, Teghil R, Zaccagnino M, Giardini A.
Emission spectroscopy of aluminum nitride plasma plume induced by ultrashort pulsed laser ablation. Appl Surf Sci 2003;209:101–6.
[13] Griem HR. Spectral line broadening by plasmas. New York: Academic Press;
1974.
[14] Handbook of materials characterization: surfaces, interfaces. In: Brundle CR,
Evans CA, Wilson Jr. S, Fitzpatrick LE, editors. Thin Films. Woburn, MA:
Butterworth-Heinemann; 1992. p. 120–1.
[15] Wang PW, Sui S, Wang W, Durrer W. Aluminum nitride and alumina
composite film fabricated by DC plasma processes. Thin Solid Films
1997;295:142–6.
[16] Brien V, Pigeat P. Microstructures diagram of magnetron sputtered AlN deposits:
amorphous and nanostructured films. J Cryst Growth 2007;299:189–94.
[17] Mahmood AM, Machorro R, Heiras J, Catrillon FF, Farias MH, Andrade E.
Optical and surface analysis of DC-reactive sputtered AlN films. Diam Relat
Mater 2003;12(12):1315–21.
[18] Caicedo JC, Pérez JA, Caicedo HH, Riascos H. Determination of physical
response in (Mo/AlN) SAW devices. Surf Rev Lett 2013;2:20–6.
[19] Raole PM, Mukherjee S, John PI. X-ray photoelectron spectroscopic study of
plasma source nitrogen ion implantation in single crystal natural diamond.
Diam Relat Mater 2005;14:482–5.
[20] Rosenberger L, Baird R, McCullen E, Auner G, Shreve G. XPS analysis of
aluminum nitride films deposited by plasma source molecular beam epitaxial.
Surf Interface Anal 2008;40:1254–61.
[21] Wolfe, William L. Handbook of optics. Vol. 2. McGraw-Hill, 2001.
[22] Antti L, Saulius N, Farshid M, Erkki I. Characterization of thin films based on
reflectance and transmittance measurements at oblique angles of incidence.
Appl Opt 2006;45:1392–6.
[23] Palik ED, Ginsburg N, Herbert BR, Holm RT. Transmittance and reflectance of a
thin absorbing film on a thick substrate. Appl Opt 1978;17:3345–7.
[24] Macleod HA. Thin-film optical filters. United Kingdom, Philadelphia, PA: CRC
Press; 2001. p. 158–9.
[25] Krupitskaya RY, Auner GW. Optical characterization of AlN films grown by
plasma source molecular beam epitaxy. J Appl Phys 1998;84:2861–6.
[26] Manova D, Dimitrova, Fukarek VW, Karpuzov D. Investigation of d.c.-reactive
magnetron-sputtered AlN thin films by electron microprobe analysis, X-ray
photoelectron spectroscopy and polarised infra-red reflection. Surf Coat
Technol 1998:205–8.
[27] Niyomsoan S, Grant W, Olson DL, Mishra B. Variation of color in titanium
and zirconium nitride decorative thin films. Thin Solid Films 2002;415:
187–94.
[28] Hunter WR. Errors in using the reflectance vs angle of incidence method for
measuring optical constants. J Opt Soc Am 1965;55:1197 (-03).
[29] Perilloux BE. Dominant wavelength sensitivity of thin-film color filters to
spectral centering. Appl Opt 1996;28:5535–9.
[30] Gadenne M, Plon J, Gadenne P. Optical properties of AlN thin films correlated
with sputtering conditions. Thin Solid Films 1998;333:251–5.
[31] Leslie S, Zakia D, Richard D. The focal encyclopedia of photography. 3rd ed..
Focal Press; 1993. p. 121 http://www.bcin.ca/Interface/openbcin.cgi?
submit=submit&Chinkey=167287.
J.A. Pérez Taborda et al. / Optics & Laser Technology 69 (2015) 92–103
[32] Connah D, Westland S, Thomson MGA. Recovering spectral information using
digital camera systems. J Colo Technol 2001;11:309–12.
[33] Angelopoulou E, Molana R, Daniilidis K, Multispectral skin color modelling. In:
Proceedings of the IEEE Conference on computer vision and pattern recognition, IEEE Computer Society Press; 1. 2001. p. 635–42.
[34] Silveira E, Freitas JA, Schujman SB, Schowalter LJ. AlN band gap temperature
dependence from its optical properties. J Cryst Growth 2008;310:4007–10.
103
[35] Ordal MA, Long LL, Bell RJ, Bell SE, Bell RR, Alexander Jr. RW, et al. Optical
properties of the metals Al, Co, Cu, Au, Fe, Pb, Ni, Pd, Pt, Ag, Ti, and W In the
infrared and far infrared. Appl Opt 1983;22:1099–121.
[36] Gorin A, Jaouad A, Grondin E, Aimez V, Charette P. Fabrication of silicon nitride
waveguides for visible-light using PECVD: a study of the effect of plasma
frequency on optical properties. Opt Expr 2008;16:13509–16.
[37] Pastrňák J, Roskovcová L. Refraction index measurements on AlN single
crystals. Phys Status Solidi 1966;14:K5–8.