MENA 9510 FME Course, 26-28 OCT 2015
Glossary
Photo-excitation
process in which light is absorbed and imparts excess energy into the material
electrons within the material move into permissible excited states
Recombination
return to equilibrium state by releasing excess energy in radiative (photon emission)
or/and nonradiative (phonon emission) processes
Photoluminescence (PL)
spontaneous emission of light from a material under optical excitation
Augustinas Galeckas
Photoluminescence spectroscopy
contactless, nondestructive method of probing the electronic structure of materials
LENS, Centre for Materials Science and Nanotechnology
Department of Physics, University of Oslo, Norway
Lecture
Background
Optical characterization methods
Interaction of light with semiconductor material
Scope
To integrate and improve knowledge on luminescence spectroscopy
To motivate and promote interdisciplinary approach in your studies
hν
By exposing both high-potential and limitations of the photoluminescence techniques
By introducing one of “less-typical” PL methods - imaging spectroscopy of defects
EMISSION
REFLECTION
Photoluminescence
Raman Spectroscopy
Photoelectron Spectroscopy
Optical Microscopy
Ellipsometry
Reflection Spectroscopy
Form
Overview of key features of the photoluminescence setup at MinaLab
PL Tutorial /”crash-course”/ based on the examples from ZnO studies
ABSORPTION
TRANSMISSION
Photoconductivity
Photoelectron Spectroscopy
Absorption coefficient
Infrared Spectroscopy
Outline
Background
Photoluminescence spectroscopy
I.
Glossary and Background
II.
Experimental considerations
Optical characterization facilities at MinaLaB/UiO
Generic time-resolved PL Imaging Spectroscopy setup
III.
IV.
EXCITATION
•By optical radiation PHOTOLUMINESCENCE
Complementary methods
Transmittance / diffuse-reflectance spectroscopy (DRS)
Transient Free-Carrier Absorption (FCA)
•By electron beams CATHODOLUMINESCENCE
Photoluminescence methods in brief
Key elements of photoluminescence analysis
“Less traditional” techniques of luminescence spectroscopy
•By fast particles (γγ-, x-rays) RADIOLUMINESCENCE
V.
Summary: Pros and Cons
VI.
Highlights
Engineering of material properties by nanostructuring and alloying
Carrier dynamics in graded bandgap ZnCdxO structures
•By AC or DC electric fields ELECTROLUMINESCENCE
LUMINESCENCE
1
DIRECT SEMICONDUCTOR
Glossary
Background
Radiative transitions
Emission spectrum
INDIRECT SEMICONDUCTOR
E
E
?
Eg
Eg
RADIATIVE
TRANSITION
PROBABILITY
hν
ν
hν
ν
?
PDIR >> PIND
?
Ep
0
k
k
BUT
EMISSION SPECTRUM
EMISSION SPECTRUM
I(ν
ν) = B(hν
ν - Eg)1/2
I(ν
ν) = B(hν
ν- Eg + Ep)2
‘WHAT IS WHAT’ IN EMISSION SPECTRUM ?
WHAT IF THERE IS NO LUMINESCENCE ?
Background
η
hν
ν
Pnr
VB
COMPETITION OF RADIATIVE AND
NONRADIATIVE RECOMBINATION
Glossary and Background
II.
Experimental considerations
Optical characterization facilities at MinaLaB/UiO
Generic time-resolved PL Imaging Spectroscopy setup
III.
Complementary methods
Transmittance / diffuse-reflectance spectroscopy (DRS)
Transient Free-Carrier Absorption (FCA)
IV.
Photoluminescence methods in brief
Key elements of photoluminescence analysis
“Less traditional” techniques of luminescence spectroscopy
V.
Summary: Pros and Cons
VI.
Highlights
Engineering of material properties by nanostructuring and alloying
Carrier dynamics in graded bandgap structures
= Pr / (Pr + Pnr)
Pr - probability of radiative transitions
Pnr - probability of nonradiative transitions
Eg
I.
Quantum Efficiency
CB
Pr
Outline
Pnr = Pnr0 exp(-E*/kT)
Thermal Quenching
η
= [1 + C exp(-E*/kT )]-1
where C = Pnr / Pr = τr / τnr
Background
Motivation
Recombination radiation
Optical characterization
techniques at Minalab
CB
ED
Eg
EA
hν
ν
• “Why”
hν
ν
* - spanning the range from wide-bandgap semiconductors (ZnO, SiC>)
to nanostructures (Er-doped Si/Ge, etc.)
hν
ν
Other potential applications:
Time-of-Flight, Transient-Absorption, etc.
VB
• “How”
EXCITATION
•BOUND
EXCITON
BE-A)
DONOR-TO-ACCEPTOR
RECOMBINATION
BAND-TO-BAND
RECOMBINATION
FREE(BE-D,
EXCITON
(FE)
ANIHILATION
•Photo generation
•FREE-TO-BOUND (FB-D, FB-A)
(DAP)
RECOMBINATION
RECOMBINATION
•Electrical injection
hν
νhole
= E- gneutral
- nEPdonor
hν
ν/ Free
= Egelectron
- EX - nE
P
(Free
- neutral
acceptor)
Need for universal characterization tool for
Temporal, Spatial and Spectral analysis of
a broad variety of luminescent materials *
Time-resolved imaging spectroscopy technique
with a single-photon sensitivity and diffractionlimited resolution
hν
ν = Eg - (EA+ED) + q2/εεr
hν
ν = Eg - EX - EA,D
2
Experimental considerations
Experimental considerations
Single-Photon Detectors
Concept:
Becker&Hickl GmbH PMC-100-4 TE-Cooled High Speed PMT
Detector Head for Time Correlated Single Photon Counting (TCSPC)
•Spectral response 185-820 nm
•Transit Time Spread 180 ps
Low-intensity optical excitation combined with a highly-sensitive
signal registration provided by single photon counting techniques*
* - offers the best price/performance value (i.e. the cheapest solution ☺)
Andor DL-658M-TIL LucaEM 14-bit TE-cooled camera uses the latest
Electron Multiplying CCD (EMCCD) Technology providing single photon
detection sensitivity.
•Active Pixels 658X496
•Pixel Well Depth (e-) 25000/100000
•Spectral response 350 - 1100 nm
•Peak Q.E. 52%
Techniques of choice:
TCSPC - Time-Correlated Single Photon Counting
for high-resolution lifetime measurements in the ps- to µs-range
MCS
- Multichannel Scaler
for lower resolution lifetime measurements ranging up to seconds
Hamamatsu H10330-75 TE-Cooled High Speed Photomultiplier Tube
(PMT) Module for NIR Photon Counting
•Spectral response 950 - 1700 nm
•Transit Time Spread 300 ps
EMCCD - Electron Multiplying Charge-Coupled Device
for imaging spectroscopy with a single-photon detection sensitivity
Experimental considerations
Experimental considerations
Time-Correlated Single Photon Counting (TCSPC)
Excitation Sources
PicoQuant LDH-375B picosecond diode laser
•Repetition rate: single shot to 40 MHz
•Pulse FWHM <70 ps
•Output power (average @40MHz) 0.3 mW
•Emission wavelength 372 nm
• Detection of single photons and the measurement of their arrival times in respect to a reference signal,
usually the light pulse
• TCSPC is a statistical method and a high repetitive light source is needed to accumulate sufficient number
of photon events
• For statistical reasons the detection of no more than one single photon event per light pulse must be ensured
KOHERAS SuperK™ 1.3 ns-pulsed super-continuum
white light source:
• 500 nm to 1750 nm ultra broad flat spectrum
• Output power 134 mW
• Repetition rate 3 - 26 kHz
Melles Griot air-cooled Argon ion cw-laser
• Output power 5 mW
• Emission wavelength 488 nm
Kimmon single-mode HeCd cw-laser
• Output power 10 mW
• Emission wavelength 325 nm
TCSPC
Experimental considerations
Experimental considerations
Time-Correlated Single Photon Counting (TCSPC)
versus Multichannel Scaling (MCS)
Mainframe Components
TCSPC works best for
• High repetition rate signals (80 MHz)
• Wavelength from 160 nm to 1000 nm
•
JobinYvonHoriba H10
High throughput fiber optic
excitation monochromator
•Spectral resolution 1 nm
TCSPC yields
Ultra-high time resolution (25 ps using deconvolution)
TTS* – Transit Time Spread
MCS
JobinYvonHoriba iHR320
Imaging Spectrograph
•
•
•
•
•
Ultra-high sensitivity - down to the single photon level
High dynamic range - high linearity
Excellent Signal-to-Noise Ratio
Useful Count Rate > 5 MHz
Short measurement times
•
•
•
MCS is a technique of choice in all other cases,
i.e. at low repetition rates, strong signals, long lifetimes, etc.
Ultra-high count rate (up to 1GHz electronically)
Many photons per shot
No dead times between bins and sweeps
Ocean Optics HR4000
High-resolution fiber optic
USB spectrometer
•Spectral resolution 0.2 nm
Janis CCS-450
Closed-Cycle Refrigerator system
•Optical cryostat is mounted on a
XYZ micro-positioner stage
•Nominal temperature range: 10–500K
3
Experimental
WHAT IF THERE IS NO LUMINESCENCE?
Time-resolved imaging spectroscopy setup
Time-resolved / Imaging / Steady-state PL
Spectral range: 330nm-1800nm
PL decay time range: 100ps-100ms
Complementary methods
Transmittance / Diffuse-Reflectance
Diffuse reflectance spectra differ from transmission equivalents
in terms of stronger than expected absorption from weak IR bands
Kubelka-Munk conversion compensates for these differences
System provides:
f(R) = (1-R)2 / 2R = K/S
Time resolved emission spectra (PL, EL) and
excitation (PLE) spectra
Spectrally-selective imaging of luminescence
morphology (2D PL patterns)
Temperature controlled measurements in the
range 10K-500K
R - absolute reflectance
K – absorption coefficient
S - scattering coefficient
WO3
Measurement
Time-resolved PL
Steady-state PL
Excitation
372nm picosecond laser diode
LDH375B (PicoQuant GmbH)
Pulse FWHM <70ps, average
power 2mW@40MHz
325nm line of a single-mode
HeCd cw-laser with output
power 10mW (Kimmon, Inc.)
Registration
Imaging spectrograph (iHR320,
Horiba Jobin-Yvon) and combined
TCSPC/MCS photon-counting
system (timeHARP / nanoHARP,
PicoQuant GmbH)
Temperature
8K-300K using closed-cycle He-refrigerator (CCS450, Janis Inc.)
WO3
Fiberoptic spectrometers with
0.2nm/2nm resolution (HR4000/
usb4000/ NIRQ512, Ocean
Optics, Inc.)
Experimental considerations
Optical characterization facilities at MinaLab/UiO
Complementary methods
WHAT IF THERE IS NO LUMINESCENCE?
Free Carrier Absorption (FCA) technique
Time-resolved imaging-spectroscopy setup with single-photon sensitivity
(TCSPC/MCS, EMCCD)
Time-integrated (fiberoptic and lock-in) low-temperature (3K-300K) UV-VISNIR (330nm-2200nm) photoluminescence setups
UV-VIS-NIR spectrophotometer: Evolution600
Diffuse-reflectance / transmittance range: 190nm – 900nm
High Temperature and Pressure Reaction Chamber:
in-situ UV-VIS measurements under controlled atmosphere
or reaction conditions up to 910°C and 34 bar
Outline
Complementary methods
WHAT IF THERE IS NO LUMINESCENCE?
I.
Glossary and Background
II.
Experimental considerations
Optical characterization facilities at MinaLaB/UiO
Generic time-resolved PL Imaging Spectroscopy setup
III.
Complementary methods
Transmittance / diffuse-reflectance spectroscopy (DRS)
Transient Free-Carrier Absorption (FCA)
IV.
Photoluminescence methods in brief
Key elements of photoluminescence analysis
“Less traditional” techniques of luminescence spectroscopy
V.
Summary: Pros and Cons
VI.
Highlights
Engineering of material properties by nanostructuring and alloying
Carrier dynamics in graded bandgap ZnCdxO structures
Free Carrier Absorption (FCA) technique
Detector
hω probe
Probe
Pump
Sample
Probe
Carrier lifetimes (2D mapping)
Surface (interface) recombination
Carrier diffusion and mobility (TG)
Pump
EG
hω pump
∆α FCA (hω probe ) = σ eh (hω probe )∆n
∆n(t ) =
∆α FCA (t )
σ FCA
=
 I 
1
ln 0 
dσ FCA  I (t ) 
4
Outline
Background
Exciton bound to Ionized Donor (D+X)
I.
Glossary and Background
II.
Experimental considerations
Optical characterization facilities at MinaLaB/UiO
Generic time-resolved PL Imaging Spectroscopy setup
III.
Complementary methods
Transmittance / diffuse-reflectance spectroscopy (DRS)
Transient Free-Carrier Absorption (FCA)
IV.
Photoluminescence methods in brief
Key elements of photoluminescence analysis
“Less traditional” techniques of luminescence spectroscopy
V.
Summary: Pros and Cons
System is similar to H2+ molecule, if σ = me/mh → 0
(D+X) exciton binding (localization) energy EB versus
donor binding energy ED (Effective Mass Theory):
Excitons bound to ionized donors show up
~10-20 meV below the free exciton line
Three-particle complex collapses, if σ = me/mh >> 1
Theory: σcritical ~ 0.45
Ionized acceptor bound excitons (A-X) do not exist in ZnO
VI.
Highlights
Engineering of material properties by nanostructuring and alloying
Carrier dynamics in graded bandgap ZnCdxO structures
σ = mh*/me* ~ 2.1 > σcritical
Energetically more favorable are neutral acceptor Ao
and free electron
Background
Background
Exciton bound to Neutral Donor (DoX)
‘WHAT IS WHAT’ IN EMISSION SPECTRUM
“Traditional” luminescence spectroscopy
System is similar to H2 molecule, if σ = me/mh → 0
(DOX) exciton binding (localization) energy EB
versus donor binding energy ED :
Near-Band-Edge
(NBE) emission
Deep-Level related Emission
(DLE)
Haynes rule:
EB(D0X) = b ED
Linear relation of donor binding energies ED
with bound exciton localization energies EB
EB = ( EFX – E DoX ) → PL(T):
Intrinsic properties (free excitons) – NBE region
Impurities/dopants (bound-excitons, DAP) - NBE and DLE
Point defects (bound-excitons, DAP) - NBE and DLE
Extended/structural defects (bound-excitons, DAP) - NBE and DLE
Background
Background
Two-electron satellites (TES) of DOX
Free Exciton (FX)
During recombination of exciton bound to neutral donor, the final state
of donor can be 1s state (normal DoX line) or the 2s/2p state (TES line).
Hydrogen model
Hydrogen-like states due to Coulomb
interaction between electron and hole:
Exciton binding energy:
Energetic distance between the DoX and its TES equals to distance
between the ground (1s) and first excited (2p) states, which is 3/4 of the
donor binding energy (ED) in the effective-mass approximation (EMA).
ZnO:
- wurzite structure
- anisotropy
- three valence bands
Donor binding energy ED can be obtained by determining position of
the related TES line:
EDoX – ETES = ¾ ED
Exciton radius:
5
Background
Background
Donor-Acceptor Pair recombination (DAP)
Deep-Level Emission (DLE)
PL of semiconductors containing substantial amounts of both donors
and acceptors can be dominated by radiative recombination processes
associated with donor-acceptor pairs (DAP).
Deep impurities/dopants (bound-excitons, DAP) - NBE and DLE
Intrinsic point defects (bound-excitons, DAP) - NBE and DLE
If a donor and an acceptor are separated by a reasonably short distance, R,
they can recombine by emitting a photon with energy:
Extended/structural defects (bound-excitons, DAP) - NBE and DLE
hv(R) = EG - ( ED + EA ) + ( e2 / ε )( a5 / R 6 )
EG – bandgap energy
ED , EA - isolated donor and acceptor binding energies
ε – static dielectric constant
a – van der Waals coefficient for neutral donor-acceptor interaction
R – separation between donor and acceptor
Recombination
Photoexcitation
Photons
For R much larger than the lattice constant (distant pairs) the discrete
emission peaks coalesce into a broad band with the peak position determined
largely by the distribution of DAP distances:
hv = EG - ( ED + EA ) + ( e2 / ε R )
Stronger Coulomb interaction of the closer pairs results in:
10-10 s
Blue-shift of DAP band with increasing excitation intensity
Narrowing and red-shift of DAP band with time delay after photo excitation
10-12 s
Capture
+
Broadening of emission
B. K. Meyer et al. phys. stat. sol. (b) 241, No. 2 (2004)
Background
Background
Near-Band-Edge Emission (NBE)
Deep-Level Emission (DLE)
Free-to-bound transitions (eA, Dh)
Free- and bound-exciton annihilation (FX, DX, AX)
Donor-to-Acceptor Pair recombination (DAP)
Deep impurities/dopants (bound-excitons, DAP) - NBE and DLE
Intrinsic point defects (bound-excitons, DAP) - NBE and DLE
Extended/structural defects (bound-excitons, DAP) - NBE and DLE
Thermalization
Recombination
10-12 s
Photoexcitation
Photons
10-5 s
Phonons
10-10 s
10-12 s
Capture
+
Broadening of emission
B. K. Meyer et al. phys. stat. sol. (b) 241, No. 2 (2004)
Background
Background
Deep-Level Emission (DLE)
Key elements of PL analysis
Temperature dependent luminescence
Bandgap narrowing (BGN) with temperature
Deep impurities/dopants (bound-excitons, DAP) - NBE and DLE
Intrinsic point defects (bound-excitons, DAP) - NBE and DLE
semi empirical Varshni
Extended/structural defects (bound-excitons, DAP) - NBE and DLE
Manoogian - Woolley model
EC
Recombination
Photoexcitation
D
DAP
eA
Dh
FX
AX
DX
Bandgap narrowing parameters (EGX, α, β, θ)
Type of transitions (eA , Dh, AX, DX, DAP)
Photons
A
Defect energy levels in ZnO according to different literature sources
+
Capture / Re-excitation
EV
6
Background
Background
Key elements of PL analysis
Key elements of PL analysis
Temperature dependent luminescence
Time-resolved luminescence
Free-carrier or exciton lifetime is a key parameter defining material
quality and device performance
Exciton lifetimes strongly depend on crystallinity and increase as the
quality of material improves
TRPL is a contactless and nondestructive method offering :
Thermal quenching of PL intensity with T
Measured lifetime
Carrier lifetime parameters
Recombination mechanisms
Carrier capture cross sections*
Crystallinity assessment
Thermal activation parameters (EBX EX EA ED )
Recombination
EC
Photoexcitation
D
FX
AX
DX
DAP
eA
NR
Photons
Capture / Re-excitation
EV
Dh
A
+
Background
Outline
Key elements of PL analysis
Temperature dependent luminescence
I.
Glossary and Background
II.
Experimental considerations
Optical characterization facilities at MinaLaB/UiO
Generic time-resolved PL Imaging Spectroscopy setup
III.
Complementary methods
Transmittance / diffuse-reflectance spectroscopy (DRS)
Transient Free-Carrier Absorption (FCA)
IV.
Photoluminescence methods in brief
Key elements of photoluminescence analysis
“Less traditional” techniques of luminescence spectroscopy
V.
Summary: Pros and Cons
VI.
Highlights
Engineering of material properties by nanostructuring and alloying
Carrier dynamics in graded bandgap ZnCdxO structures
Line-width broadening with temperature
Line-width parameters of excitonic emission (Γ0, γ):
Qualitative crystallinity assessment
Dominant mechanism of scattering
Background
Background
Key elements of PL analysis
“Less traditional” spectroscopy
Excitation dependent luminescence
Spatially-resolved luminescence techniques
IPL = (Iex)k
k < 1:
1 < k < 2:
3C-SiC
Scanning spectroscopy (µPL, CL)
intensity as a function of excitation
Imaging spectroscopy (PL, PLE, EL)
free-to-bound (Dh, eA) and DAP
excitonic transitions (FX, DX, AX)
Both approaches are capable of mapping extended
(structural) defect and carrier lifetime distributions
Important difference:
Imaging spectroscopy also allows to study in situ
the dynamics of structural instabilities*
Photoluminescence yield versus excitation intensity:
4H-SiC
Type of transition (eA, Dh, DAP vs FX, AX, DX)
Concentration of defects (via saturation curves)
7
Background
Background
Spatially-resolved CL
Imaging spectroscopy of structural defects in 4H-SiC
Localized recombination at extended
defects such as dislocation loops
Dislocations may act as radiative and
non-radiative recombination centers
Excitons bound at structural defects
Stacking faults (SF)
Bounding partial dislocations
Screw and Edge threading dislocations
Defect visualization by spectrally filtrated EL/PL
Secondary electron microscopy (SEM) and
cathodoluminescence (CL) cross section images
of bulk ZnO
B. K. Meyer et al. phys. stat. sol. (b) 241, No. 2 (2004)
Background
Imaging PL spectroscopy of
structural defects
PL(3K) morphology of epitaxial ZnO layers
grown on different ZnO substrates:
Background
Note on comparability of PL results and possible data misinterpretation
PL measurement results strongly depend on experimental conditions
Often underestimated influence of probe beam size and excitation intensity
i.
Small probe area, i.e. tightly focused excitation beam, provide local instead
of statistically average properties of the material due to possible onset of:
extended defects, grain boundaries, etc. (ZnO)
microscopic potential fluctuations (MgxZnO, CdxZnO)
modification of material properties by excitation beam itself:
charging, annealing, structural degradation (SiC)
ii.
Spectral shape in general is intensity-dependent due to saturation effects
of different recombination channels
iii.
Unaccounted PL measurement artifacts
(optical interference effects, parasitic signal from surface, etc.)
.
Things to remember:
i.
ii.
Note bright-line character of dislocation network
Note dark-line character of dislocation network
Only statistically-validated measurement results matter
(one probe position is usually not enough)
Crystal quality assessment requires identical experimental conditions
throughout all measurements (intensity, incident angle, temperature, etc.)
Background
Background
Imaging spectroscopy of structural defects in ZnO
Beam interaction with matter: optically induced structural defects in SiC
Stacking Faults in 4H-SiC and 3C-SiC
Spatially-resolved PL(10K) spectra from dislocation in ZnO
8
Background
Summary
Spectral shape deviation
Photoluminescence (PL) is a spontaneous emission of light from a material under optical excitation.
PL spectroscopy is a selective and extremely sensitive probe of discrete electronic states.
Analysis of emission spectra allows to identify surface, interface and impurity levels and to estimate crystallinity of the material.
PROS:
PL analysis is nondestructive: technique requires very little sample manipulation or environmental control.
Optical excitation makes electrical contacts and junctions unnecessary, high-resistivity of materials pose no practical difficulty.
Thermally activated processes can be characterized via corresponding changes in PL intensity with temperature.
Time-resolved PL can be very fast, making it useful for characterizing the most rapid processes in a material.
CONS:
Fundamental limitation of PL analysis is its reliance on radiative events: materials with poor radiative efficiency, such as
low-quality indirect bandgap semiconductors, are difficult to study via ordinary PL techniques.
Identification of impurity and defect states is dependent on their optical activity. In order to conclusively identify the nature
of defects, PL studies usually have to be combined with other experimental techniques:
Carrier-concentration measurements (Hall)
Electron paramagnetic resonance spectroscopy (EPR)
Positron annihilation spectroscopy (PAS)
Deep level transient spectroscopy (DLTS)
Secondary ion mass spectroscopy (SIMS)
X-ray photoelectron spectroscopy (XPS)
Saturation of deep-level recombination with increase of excitation/injection
Outline
Outline
I.
Glossary and Background
I.
Glossary and Background
II.
Experimental considerations
Optical characterization facilities at MinaLaB/UiO
Generic time-resolved PL Imaging Spectroscopy setup
II.
Experimental considerations
Optical characterization facilities at MinaLaB/UiO
Generic time-resolved PL Imaging Spectroscopy setup
III.
Complementary methods
Transmittance / diffuse-reflectance spectroscopy (DRS)
Transient Free-Carrier Absorption (FCA)
III.
Complementary methods
Transmittance / diffuse-reflectance spectroscopy (DRS)
Transient Free-Carrier Absorption (FCA)
IV.
Photoluminescence methods in brief
Key elements of photoluminescence analysis
“Less traditional” techniques of luminescence spectroscopy
IV.
Photoluminescence methods in brief
Key elements of photoluminescence analysis
“Less traditional” techniques of luminescence spectroscopy
V.
Summary: Pros and Cons
V.
Summary: Pros and Cons
VI.
Highlights
Engineering of material properties by nanostructuring and alloying
Carrier dynamics in graded bandgap ZnCdxO structures
VI.
Highlights
Engineering of material properties by nanostructuring and alloying
Carrier dynamics in graded bandgap ZnCdxO structures
Compendium
MENA 9510 FME-Course, 26-28 OCT- 2015
Luminescence spectroscopy
Universal tool for:
Fundamental studies of material properties
Application-driven characterization of semiconductors
Assessment of crystallinity
Identification/monitoring of defects and impurities
Allows characterization of :
Intrinsic properties (free excitons)
Impurities/dopants (bound-excitons, DAP)
Point defects (1D: interstitials, vacancies, complexes)
Extended/structural defects (2D, 3D: dislocations, stacking faults, etc.)
Key elements of luminescence analysis:
Quantum efficiency of luminescence
Excitation intensity dependent luminescence
Identification of optical transition types
(DX, AX, FX, eA, Dh, DAP)
Time resolved luminescence
Carrier lifetime parameters
Recombination mechanisms
Thank you for attention!
Temperature dependent luminescence
Thermal activation parameters (EBX EX EA ED )
Bandgap narrowing parameters (EGX, α, β, θ)
Line-width (Γ0) and broadening parameters
Common forms of implementation:
Steady-state luminescence (PL, CL)
Time-resolved luminescence (PL, CL)
Photoluminescence excitation spectroscopy (PLE)
Spatially and depth-resolved luminescence (PL, CL)
9