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Dilute Nitrides – growth, characterisation
and mid-infrared applications
A. Krier, M. de la Mare, P. Carrington, Q. Zhuang, M. Kesaria, M. Thompson
Physics Department, Lancaster University, UK
Optics 2014
Outline

Dilute Nitrides
MBE growth on InAs and GaAs
Structural and transport properties
PL and EL
Addition of Sb
Devices

Summary
N
Motivation
-1
Wavenumber ( cm )
•
Gas sensors - optical absorption;
•
•
•
•
•
CH4, CO2, CO
Industrial process control
Spectroscopy
Thermal imaging
Bio-medical diagnostics
Military - infrared countermeasures
Transimission ( % )
2000
100
50
2400
CO
5
4.5
3200
HCN
CO2
NO2
0
2800
HCl
HCN
NO2
CH4
CO
CO2
HCl
4
3.5
Wavelength ( m )
CH4
3
Principal gas absorptions in the mid-infrared
For these applications we need LEDs, lasers and detectors operating
at Room Temperature
Dilute nitrides and the Mid-infrared
Problems :- imbalance in the DOS of InAs
Auger recombination (CHSH)
CB
Inter-valence band absorption (IVBA)
Inadequate electrical confinement
-small band offsets
- No SI substrates
Addition of N : Band anti-crossing effect
- flexible wavelength tailoring
without complex growth
1
1’
2’
Eg
HH
2
LH
Higher effective mass
than in InAs or InSb and equalises DOS
Superior bond strengths and material stability
Compared to CdHgTe
InAsN dilute nitride alloys offer some possibilities for improvement
Δ0
Band anti-crossing
An empirical model
Extended-localized state interaction
E (k )  ECB (k )
V
E (k ) 
V
E ( k )  EN
Anticrossing/repulsion between conduction-band edge and localized states
2
the
band gap
EN  ECB (k )
(
k
)
 EN  Edecreases

2
CB
E ( k ) 
introduces

  Vat low k-value in the CB
minigap(s)
2
2


2.00
GaAsN
E (k) (eV)
E+
1.80
EN
ECB
1.60
E1.40
-5.00
0.00
8
5.00
-1
k (10 m )
W. Shan et al., Phys. Rev. Lett. 82, 1221 (1999)
Band structure
CB
N levels
N-N pairs & clusters
N related
defects
The band structure of III-VNs is determined by the
distribution of energy levels
due to N-impurities and Nclusters and their
hybridization with the
extended CB states
VB
GaAsN
N-level
CBE
0.2 eV
InPN
0.4 eV
InAsN
N-pairs and clusters
DE = 1 eV
E.P. O’Reilly et al., SST 24 033001 (2009)
E. P. O‘Reilly, A. Lindsay, and S. Fahy, J. Phys. Cond. Matt., 16, S3257 (2004)
MBE Growth on InAs and on GaAs
V80 Molecular Beam Epitaxy (VG)
with RF Plasma Nitrogen source, As and Sb valved cracker cells (EPI)
Ga, In, Al and dopants GaTe and Be
Sample TG
A0276
A0282
A0285
A0299
A0300
485
420
442
376
450
Flux - As
Flux - N2
Plasma
Power
N Content
6.6x10-6
2.2x10-6
2.2x10-6
2.2x10-6
2.8x10-6
n/a
6.12x10-7
6.12x10-7
6.3x10-7
5.0x10-7
n/a
160
160
160
160
n/a
0.6
0.2
1.0
0.4
%
Large parameter space for InAsN
InAsN successfully grown on InAs with N < 2% and PL observed out to 4.5 µm
For growth on GaAs
Optimum growth at substrate temperatures between 4000C- 4400C
Nitrogen plasma setting fixed at 160 W with flux of 5x10-7 mbar
Growth rate of ~1µm per hour
InAs control sample was grown under the same conditions
X-ray diffraction
2 different layer peaks
obtained - 2 dominant N
compositions
Plastic relaxation
-Vertical and horizontal lattice
deformations obtained
-Gives relaxed lattice const.
and plastic deformation R
Layers with N< 1.2% are
pseudomorphic
Bragg maps narrow in qII
N > 1.2% more diffuse
scattering from misfit
dislocations & defects
Onset of plastic relaxation at
N~ 1.4%
asymmetrical (224) reflections measured for all samples
N=0.83% - tail indicates vertical N
composition gradient
N=0.34% - thickness fringes – good interface
quality
Growth rate decreases with increasing N
SIMS and TEM analysis
Sample : A0299 InAsN 1% N
1.0E+07
Intensity (cs-1)
1.0E+06
1.0E+05
Ga
As
InAs/GaAs
In
200 nm
1.0E+04
1.0E+03
N
1.0E+02
1.0E+01
InAsN(1%) /GaAs
1.0E+00
0.00
0.50
1.00
1.50
2.00
200 nm
Depth (microns)
N is uniform
No evidence of unintentional impurities (C, O etc.) as-grown InAsN is of high purity
Analysis of secondary ion peaks from CsAsN+ enables accurate N determination
-comparison with XRD data – N content is ~5% larger than determined from XRD
Significant incorporation of non-substitutional N
Higher dislocation density in InAsN – but obtain increase in PL
Localisation, non-uniform PL emission from regions around dislocations?
Raman spectroscopy
Weak InAs modes at 405 and 425 cm−1 and
2nd order InAs optical modes at 435, 450, 460 and 480cm−1
N related
features
Additional N related features at 402, 415, 428 and 443 cm−1
(previously observed by Wagner et al. N ~ 1.2 %)
2nd order InAs modes
NAS
As -N
N-N
difference spectrum of highest N – lowest N content
443 cm−1 feature - also detected in FTIR
NAs LVM from substitutional 14NAs
402 cm−1 and 415 cm−1 peaks from non-substitutional N-N
or As-N split interstitials, (N antisites or interstitial N) rather
than N-In-N complexes
and As -N produce deviations from Vegard’s law
(Calculations predict N-N split interstitial at 419 cm−1
but also predict that the As-N split interstitial lies well
above the LVM in GaAsN)
Ibanez et al, JAP (2010)
Electrical properties InAsN on GaAs
1
10
T = 293 K
5
3
-1
Ga(AsN)
2
impurity scattering
-2
10
0.0
0.4
0.8
1.2
1.6
N (%)
2
-1 -1
Mobility (m V s )
77K
InAsN
1
0.1
GaAsN
0.01
0.0
0.1
0.2
0.3
0.4
N-content (%)
0.5
0.6
A. Patanè et al Appl. Phys Lett. 93, 25106 (2008)
-3
0.5
x (%)
16
10
1.0
1000 nm n-type InAs(N)
10
T (K)
10
0.0
1
0.4%
0.6%
1.0%
1
T = 293K
2
0.2%
10
nH (cm )
2 -1 -1
 (m V s )
x=0%
4
-1 -1
Phonon scattering
0
10
H (m V s )
In(AsN)
17
10
100
0
Semi-insulating GaAs substrate
N reduces electron mobility
µ is limited by electron scattering by N-atoms, -pairs and clusters
Model for GaAsN predicts a strong reduction of the mobility and
electron mean free path due to the N-levels
Weak dependence of µ on N-content compared to GaAsN due to
the proximity of the N-related states to the CBE
Impurity scattering dominant at high N
Residual carrier conc. increases for N >0.4%
N incorporation introduces native donor states
Electron Cyclotron Mass
The cyclotron mass increases with increasing x
Comparing the N-induced change of the
mass in InAsN and GaAsN
0.030
(me)
me*/m0
0.035
GaAsN LCINS,
O’Reilly
0.025
11.4 m
66.0 m
0.0
0.5
1.0
15.0 m
103.0 m
1.5
2.0
N (%)
CR/PR GaAsN
CR InAsN
The electron mass and its dependence
on the excitation energy are weakly
affected by the nitrogen
O. Drachenko et al. APL 98, 162109 (2011)
InAsN - Cyclotron Resonance
0.5
EF= 10 meV
18
2.0%
0.4
EF
-3
n (cm )
10
1.0%
 (eV)
80 meV
40 meV
20 meV
N = 0%
0.3
17
10
-4x10
6
0
-1
k (cm )
4x10
6
Pinning of the Fermi level
16
10 0.0
0.5
1.0
N (%)
1.5
2.0
The increase of electron density with
increasing N indicates a pinning of the Fermi
level and implies a substantial density of
native donor states
O. Drachenko et al. APL 98, 162109 (2011)
Photoluminescence InAsN on InAs
Incorporation of small amounts of N into III-V’s causes
conduction band anti-crossing leading to reduction in
band gap
Good agreement with band anti-crossing model
(60 meV per 1%N)
Long low energy tail appears - localisation
CMN = 2.5 eV at 4 K
caused by uneven nitrogen distribution- composition
fluctuations or point defects
0.355
Band Gap Energy (eV)
0.350
0.345
0.340
0.335
0.330
-4 2
Eg=0.353-[1.1x10 T /(T+100)]
0.325
0
50
100
150
200
Temperature (K)
250
300
6.5
Photoluminescence Lineshape
6.0
5.5
4K
20K
40K
60K
80K
100K
120K
150K
180K
210K
240K
270K
300K
5.0
4.5
Intensity
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.26 0.28 0.30 0.32 0.34 0.36 0.38 0.40
Photon Energy (eV)
PL is Gaussian at low T
As T increases becomes asymmetric with high energy tail
extends well above Eg
Conduction Band
Lineshape - 2 effects
Localization at low T
Free carrier emission at high T
J. Appl. Phys. 108, 103504 (2010)
Valence Band
InAsN on GaAs
0.6%N
10
Good agreement with band anti-crossing
model
Inclusion of nitrogen improves the peak
intensity InAsN > InAs on GaAs
Photoreflectance shows Δ0 is constant with
increasing N
Activation energy increases with increasing N
content – CHSH Auger detuning
4K PL
0.4%N
8
Intensity (a.u.)
PL obtained from InAsN on GaAs across the
mid-IR spectral range with addition of small
quantities (~ 1%) of nitrogen
1%N
0.2%N
6
improved PL
InAs/GaAs
4
CO2
2
0
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
Wavelength (m)
0
D0
0.40
Energy (eV)
Normalised PL Intensity (a.u.)
10
0.35
E0
InAsN/InAs
InAsN/GaAs
InAsN/InAs E0
0.30
InAs/InAs
InAs/GaAs
InAsN(0.6%)/GaAs
InAsN(1%)/GaAs
-1
10
-2
10
InAsN/InAs Do
0
BAC model
0.0
0.5
1.0
1.5
2.0
Nitrogen content (%)
2.5
3.0
50
100
150
200
Temperature (K)
250
300
4.6
Adding Sb - MBE growth of InAsSbN
InAs
Adding N to
InAs
Conduction band
Adding Sb to
InAs
Eg
Valence band
Increasing N
Increasing Sb
Tensile strain
Compressive strain
N is hard to incorporate
Use Sb to reduce lattice mismatch increase N
incorporation improve quality
Sb acts as surfactant to maintain 2D growth and
reduces point defects - improves PL
Red-shift of emission wavelength
– need less N to reach longer wavelengths
Sb reduces N surface diffusion length - increases N
incorporation ~ 2.5x
Reduction of Sb segregation induced by N increases Sb incorporation ~1.5x
Photoreflectance
Δso > E0 Auger suppression
Advantage of InAsNSb over InAsN
In-plane strain for layers grown on InAs
can be tuned from tensile to compressive
- Tailor polarization in QW to be either TE or TM
Sb increases confinement in valence band
- dominant polarisation is TE (e1-hh1)
0.8
0.8
Spin orbit splitting In InNAs & InAsNSb
E0
E0+DSO
DSO
0.5
E0+DSO
DSO
Fit
Fits for InNAs
0.4
0.4
0.3
0.5
0.3
(c) InNAs
0.0
0.5
1.0
1.5
2.0
Nitrogen concentration (%)
InNAs
Kudrawiec et al. APL 99, 011904 (2011)
Incorporation of Sb increases Δso and
decreases E0
N does not change Δso
DSO
0.6
2.6% Sb
4.1% Sb
7.0% Sb
7.3% Sb
Ref.[31]:
E0
4.8% Sb
This work:
E0
Energy (eV)
Energy (eV)
0.6
E0+DSO
0.7
0.7
Both Sb and N reduce E0
(d) In(N)AsSb
0.0
0.5
1.0
1.5
2.0
Nitrogen concentration (%)
InNAsSb
~ 5 meV per 1% of Sb
~ 60 meV per 1% N
InAsSbN Photoluminescence
Strong PL at room temperature
- good optical quality
Asymmetric shape
Narrow energy gap – free carrier
emission is important
Especially > 100 K
High energy tail extends well above Eg
Latwoska et al, Appl. Phys. Lett 102, 122109 (2013)
Gaussian at low T
PL peak lower than Eg determined from PR
Characteristic S-shape but with weak carrier
localisation
- Stokes shift <10 meV
smaller than for InAsN
Composition fluctuations or point defects reduced
due to surfactant effect of Sb
InAsN QW lasers on InP
InAsN ridge lasers operating up to 2.6 µm have been demonstrated – grown by gas source MBE
limited by N incorporation and critical thickness
4 QW InAsN/InGaAs on InP (5μs pulse width, 500 Hz repetition rate)
Max. operating temperature 260 K with T0 = 110 K
Decreasing growth temp incorporates more N
….but reduces QW quality
D. K. Shih, H, H. Lin, and Y. H. Lin, IEE Proc. Optoelectronics 150, 253 (2003)
InAsN MQW grown by MOVPE
MQW containing 18% N
on GaAs (UNM)
-longest wavelength PL obtained from dilute N
growth temperature 500 0C
Osinski , Optoelectronics Review 11(4) 321-6 (2003)
InAsSbN / InAs MQWs
100 nm InAs Capping
Layer
10x InAsNSb /InAs QW
(12x24 nm)
200 nm InAs Buffer
Layer
Growth of the
MQWs calibrated
using the same
growth method of
previously grown
InAsNSb bulk layers
InAs substrate
200 nm InAs Buffer layer grown at 480°C
10x InAsSbN/InAs QW grown at 420°C
• Growth rate of 0.5µm per hour
-6
• Nitrogen plasma setting fixed at 160 W with flux of 6×10 mbar
100 nm InAs Capping Layer grown at 480°C
As flux kept at minimum for growth of InAs layers
∆EV =
102meV
InAs
hh1 = 9meV
hh2 = 36meV
InAs0.92Sb0.08 InAs
InAsSbN/InAs MQW 4K photoluminescence
7
5
4
3
2
Peak Wavelength
tot=3.62m
e - hh1
4K
0.009
=3.68m
0.008
e1-hh1
e - lh1
=3.48m
2.6
2.8
3.0
3.2
3.4
4K
N =1%, Sb 6%
4.38 m Bulk
0.007
e1-lh1
3.6
3.8
4.0
4.2
4.4
4.6
Wavelength (m)
Intensity (a.u.)
Relative Intensity (a.u.)
6
1.8W
1.6W
1.2W
1W
0.8W
0.6W
0.5W
0.4W
0.2W
0.1W
0.06W
0.03W
0.006
3.62 m MQW
0.005
0.004
0.003
0.002
0.001
1
0.000
0
-1
3.0
-0.001
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
3.2
3.4
3.6
3.8
4.0
Wavelength (m)
No blue-shift with excitation power
- Type I QW
3.48 µm
3.62 µm (expt.)
4.2
4.4
Wavelength (m)
Band alignment determined by modification of
InAsSb - Type II alignment with conduction and
valence band offsets of 39 & 82 meV
ADDITION OF N :
• Reduction in overall strain
band gap
Reduction of
• Conduction band further reduced by BAC model
Reduction of 63 meV
50
InAsSbN MQW LED
25mA
50mA
75mA
100mA
150mA
200mA
300 K EL
40
EL Intensity (a.u.)
p-i-n diode containing 10x
InAsSbN QW in active region N =1%, Sb 6%
p InAs
InAsNSb MQW
n InAs
30
C-H
absorption
20
InAs (100) substrate
10
p+-InAs
n+-InAs
0
2500
3000
3500
Wavelength (nm)
Longest wavelength dilute nitride
light emitting device to date
0.07
12
4 K EL
Intensity (a.u.)
0.05
10
Outout Power (W)
30mA
50mA
75mA
100mA
150mA
4K
0.06
8
6
4
0.04
0.03
0.02
InAsSbN e-hh1
InAsSb e-hh1
InAsSb e-hh2
0.01
2
0.00
2.5
0
50
100
150
200
Current (mA)
250
300
3.0
3.5
4.0
4.5
Wavelength (m)
LED output power : 6 µW at 100 mA drive current and internal RT efficiency ~ 1%
4000
4500
InAsSbN MQW p-i-n photodetector
0.1
4K
20K
40K
60K
80K
100K
120K
140K
160K
190K
220K
250K
280K
300K
Current (A)
0.01
1E-3
1E-4
1E-5
EL emission (a.u)
-0.5
1.5
2.0
2.5
3.0
3.5
4.0
0.5
1.0
1.5
10
9
8
7
6
2
0.1
1.0
0.0
Voltage (V)
R0A (cm )
1
1E-6
R0A ~1/n
5
4
2
(R
 1/n
R 0AA)~1/n
3
2
0
4.5
Wavelength (m)
3
4
5
6
7
8
9
10
11
12
13
-1
1000/T (K )
A0363
4.00E+017
3.50E+017
3.00E+017
2.50E+017
17
-2
NA = 8.3x10 cm
-3
2.00E+017
-2
Cut-off λ ~ 4 μm
Ideality factor = 1.6
R0A
T<120 K generation-recombination dominates
T>220K diffusion limited recombination is
dominant
Capacitance at 0V =2.54 nF
Built in potential = 0.19 V
Carrier concentration = 8.3x1017 cm-3
2
C (F )
Photoresponse (a.u.)
10
1.50E+017
1.00E+017
5.00E+016
2
2
1/C =2(Vbi-V)/A qNA
Slope = NA
Vbi=0.19V
x-intercept = Vbi
0.00E+000
-0.20 -0.15 -0.10 -0.05 0.00
0.05
0.10
Voltage (V)
0.15
0.20
0.25
0.30
0.35
New prospects
Recent results on rapid thermal annealing
(RTA) show a large x20 increase in PL
intensity of InAsN
-no increase in residual carrier
concentration
H irradiation also increases PL intensity
In InAsN
GaAsN +H results in passivation of N which
restores the bandgap (reversibly)
Can create GaAsN quantum dots
hydrogen
GaAsN
GaAs
Change to GaInAsN - single photon sources
Micro – LED arrays
Summary
The successful MBE growth of InAsN directly onto InAs and GaAs substrates
has been obtained with N up to ~ 2%
Behaviour of N in InAs different to N in GaAs
Mobility is reduced but shows weak dependence on N content
Fermi level pinning and native donor states
PL was obtained which covers the mid-infrared (2-5 μm) spectral range in good
agreement with the BAC model
Localisation and free carrier effects are important in interpretation of PL spectra
N reduces band gap but has little effect on T sensitivity
Photoreflectance shows N has no effect on Δo
Auger CHSH de-tuning is possible
Addition of Sb increases N incorporation –structural and optical properties
- improved and bright PL obtained from Type I InAsSbN/InAs MQWs
First long wavelength dilute N LED operating at 300 K
good prospects for device applications if electron concentration can be controlled
Acknowledgements
A. Patane
Nottingham University
Transport measurements
R. Beanland & A. Sanchez
University of Warwick
TEM
J. Ibanez
University of Madrid
Raman spectroscopy
R. Kudrawiec
M. Latkowska
Institute of Physics, Wroclaw
Photoreflectance
O. Drachenko
M. Helm
Helmholtz-Zentrum
Dresden-Rossendorf
Cyclotron resonance
M. Schmidbauer
Leibniz-Institute, Berlin
X-ray diffraction
Financial support from EPSRC (EP/G000190/01) and also for providing a studentship for M. de la Mare
Comparison with InAsSb
0.012
Intensity (a.u.)
0.010
4K
20K
40K
60K
80K
100K
120K
140K
160K
190K
220K
250K
280K
300K
InAsSbN MQW LED
N =1%, Sb 6%
0.008
0.006
0.004
0.002
2400
2600
2800
3000
3200
3400
3600
3800
4000
InAsSbN e-hh1
InAsSb e-hh1
InAsSb e-hh2
4200
Wavelength (nm)
Comparison of the temperature dependence
of the EL with that of type II InAsSb/InAs
reveals more intense emission at low
temperature
Improved temperature quenching up to
T~200 K where thermally activated carrier
leakage becomes important and further
increase in the QW band offsets is needed
Increasing the nitrogen content above 0.5%
reduces the band gap sufficiently such that
the energy gap Eo becomes less than Δso
effectively detuning the CHSH Auger
recombination mechanism
PL analysis temperature dependence
8
4K
20K
40K
60K
80K
100K
120K
140K
160K
190K
220K
250K
280K
300K
A0299
7
Intensity (a.u.)
6
5
4
3
2
CO2
1
0
-1
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
Wavelength (m)
1.0
300K
Intensity (a.u.)
0.8
0.6
CO2
0.4
0.2
0.0
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
Wavelength (m)
InAsN(1%) exhibits very weak temperature quenching ~ 8x
PL emission obtained up to room temperature without annealing
Peak wavelength near 4 µm – appropriate for CO2 detection
4.2
4.4
4.6
Comparing III-N-Vs
InAsN
Energy
Eg-G = 0.35 eV
EL=1.08 eV
EX=1.37 eV
X-valley
G-valley
GaAsN
Energy
X-valley
N
<100>
G-valley
L-valley
Eg-G = 1.42 eV
EL~0.3 eV
EX~0.3 eV
L-valley
N
<111>
<100>
<111>
Wave vector
The energy of the N-level (EN~ 1eV)
is larger than the threshold energy
for impact ionization (~ Eg-G).
The energy of the N-level (EN~ 0.2eV)
is smaller than the threshold energy for
impact ionization (~ Eg-G).
InAsN - Cyclotron Resonance
Magneto-transmission in pulsed magnetic field B up to 60T and monochromatic excitation by QCL
Minimum at the resonance field Bc gives me* = eBC/(2c)
x=0%
me *  0.025me
Transmission (arb. units)
 e ~ 0.20 ps
0.4%
0.6%
CR quenches in GaAsN (0.1%) due to low μ
NN=
= 0%
0%
1
1.1 %
me *  0.027me
 e ~ 0.15 ps
me *  0.029me
 e ~ 0.1 ps
Transmission
T =100 K
u= 2.9THz
InAs1-xNx m*  eB / 2
e
c
1.9%
Nx =
1.1%
= 1.1%
11.4m
1.0%
me *  0.060me
 e  0.1ps
0
2
4
6
B (T)
8
 = 11.4 µm
 = 66.0m 15.0m
0
0
0
20
T = 4.2K
40
20
B(T)
40
10
Patanè et al. PRB 80 115207 (2009)
Area of the CR minimum gives electron density n
60
Photoreflectance Spectroscopy
PR spectra can be fitted using
InAsN on InAs
where C and θ are amplitude and phase
m=2.5 for b-b
Avalanche photodiodes
InAsN
Energy
Eg-G = 0.35 eV
EL=1.08 eV
EX=1.37 eV
X-valley
G-valley
GaAsN
Energy
X-valley
N
<100>
G-valley
L-valley
Eg-G = 1.42 eV
EL~0.3 eV
EX~0.3 eV
L-valley
N
<111>
<100>
<111>
Wave vector
The energy of the N-level (EN~ 1eV)
is larger than the threshold energy
for impact ionization (~ Eg-G).
The energy of the N-level (EN~ 0.2eV)
is smaller than the threshold energy for
impact ionization (~ Eg-G).
InAsN: Impact Ionization
0.1
x=0.6%
x =0.6%
L=2m
5 m
10m
x =0%
I (A)
0.06
0.0
0.00
0
2
Rapid increase of current at large electric
fields (>1kV/cm) due to impact ionization
(IO).
4
x=0%
I
L=2m
5 m
0.05
2m
T=77K
-0.1
W = 5m
L = 10m
-4
10m
0.00
0
-2
0
V (V)
2
2
4
4
At x~1%, electric fields for impact ionisation are larger than those measured in InAs,
although the threshold energy is smaller
The reduction of the band gap energy by the N-atoms combined with impact
ionization is of interest for IR-Avalanche Photodiodes
Makarovsky et al., APL 96, 052115 (2010)
Dilute nitrides
D. Sentosa, X. Tang,a, and S.J.
Chua, Eur. Phys. J. Appl. Phys.
40, 247–251 (2007)
InAs
N introduces tensile strain (on InAs or GaAs)
disorder and strong bowing
Harris, J. S. Semiconductor Science and Technology 17, 880 (2002)
InN
N
InAsN Photoreflectance
Solid lines are fits to
Where, x is the N content
N does not change Δso
Photoluminescence curve fitting
Fit using
Includes localized and band-band transitions
A = scaling factor
Ecr = energy of crossover between equations
K = smoothing parameter
σ relates to slope of DOS
Set K = kBT/σ and Ecr = Eg + kBT/σ
n= 0.5 to 2 for momentum conserving non-conserving
transitions
Black arrows – Eg determined from PL fitting
Red arrows – PL peak
Best fit when n=1
Note the difference which increases with T
Latwoska et al, Appl. Phys. Lett 102, 122109 (2013)
Temperature dependence
Eg obtained from PL
spectral fitting
deviates from PL peak
value especially at
T> 80K
Free carrier emission
must be taken into
account
Bose-Einstein formula
fitting gives: e-phonon coupling constant, αB ~ 20 meV and average phonon
temperature, θB ~ 140 K
N incorporation significantly reduces Eg in InNAsSb but has almost no effect on
temperature dependence
Temperature dependence of bandgap
Comparison of change in energy gap with T
InNAsSb 65 meV
whereas 1% N in GaAs reduces T dependence of Eg by 40%
InAs
66 meV
InSb
62 meV
BAC model gives good agreement
T dependence of Eg in InNAsSb is not
sensitive to N due to large separation
between EN and EM (~ 1 eV)
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