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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 NitridesMBE growth on InAs and GaAs Structural and transport propertiesPL and EL Addition of Sb Devices

Summary

N

Motivation

• Gas sensors - optical absorption;

CH4, CO2, CO • Industrial process control• Spectroscopy• Thermal imaging• Bio-medical diagnostics • Military - infrared countermeasures

Principal gas absorptions in the mid-infrared

5 4.5 4 3.5 30

50

1002000 2400 2800 3200

HCN

CH4

HCl

CO2

NO2

CO

Wavelength ( m )

HCl HCN NO2 CH4 CO CO2

Tra

ns

imis

sio

n (

% )

Wavenumber ( cm-1 )

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)

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

Higher effective massthan in InAs or InSb and equalises DOS

Superior bond strengths and material stabilityCompared to CdHgTe

InAsN dilute nitride alloys offer some possibilities for improvement

2’1’

2

1

CB

LH

HH

Eg

Δ0

1.40

1.60

1.80

2.00

-5.00 0.00 5.00

E (

k) (

eV)

k (108 m-1)

W. Shan et al., Phys. Rev. Lett. 82, 1221 (1999)

An empirical model

ECB

EN

E+

E-

N

CB

)(

)()()(

EkEV

VkEkEkE

22

CBNCBN

2

)(

2

)()( V

kEEkEEkE

Extended-localized state interaction

Anticrossing/repulsion between conduction-band edge and localized states decreases the band gap

introduces minigap(s) at low k-value in the CB

Band anti-crossing

GaAsN

GaAsN InPN InAsN

N-levelCBE

0.2 eV 0.4 eV

DE = 1 eV

N-pairs and clusters

E.P. O’Reilly et al., SST 24 033001 (2009)

The band structure of III-V-Ns is determined by the distribution of energy levels due to N-impurities and N-clusters and their hybridization with the extended CB states

N levelsN-N pairs & clustersN relateddefects

CB

VB

E. P. O‘Reilly, A. Lindsay, and S. Fahy, J. Phys. Cond. Matt., 16, S3257 (2004)

Band structure

MBE Growth on InAs and on GaAsV80 Molecular Beam Epitaxy (VG) with RF Plasma Nitrogen source, As and Sb valved cracker cells (EPI)Ga, In, Al and dopants GaTe and Be

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 hourInAs control sample was grown under the same conditions

Sample TG Flux - As Flux - N2Plasma Power

N Content %

A0276 485 6.6x10-6 n/a n/a n/aA0282 420 2.2x10-6 6.12x10-7 160 0.6A0285 442 2.2x10-6 6.12x10-7 160 0.2A0299 376 2.2x10-6 6.3x10-7 160 1.0A0300 450 2.8x10-6 5.0x10-7 160 0.4

X-ray diffraction

N=0.83% - tail indicates vertical N composition gradientN=0.34% - thickness fringes – good interface quality

Growth rate decreases with increasing N

asymmetrical (224) reflections measured for all samples

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 pseudomorphicBragg maps narrow in qII

N > 1.2% more diffuse scattering from misfit dislocations & defects

Onset of plastic relaxation at N~ 1.4%

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.601.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+07

Sample : A0299 InAsN 1% N

Depth (microns)

Inte

ns

ity

(c

s-1

)SIMS and TEM analysis

N is uniform

No evidence of unintentional impurities (C, O etc.) as-grown InAsN is of high purityAnalysis 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?

InAs/GaAs

InAsN(1%) /GaAs

200 nm

200 nm

As

In

N

Ga

Raman spectroscopy Weak InAs modes at 405 and 425 cm−1 and 2nd order InAs optical modes at 435, 450, 460 and 480cm−1

Additional N related features at 402, 415, 428 and 443 cm−1

(previously observed by Wagner et al. N ~ 1.2 %)

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 complexesand 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)

N related features

NAS As -N N-N

Ibanez et al, JAP (2010)

2nd order InAs modes

0.0 0.4 0.8 1.2 1.610-2

10-1

100

101

Ga(AsN)

(m

2 V-1s-1

)

N (%)

T = 293 K

In(AsN)

0.0 0.1 0.2 0.3 0.4 0.5 0.60.01

0.1

1

10

GaAsN

Mob

ility

(m

2V

-1s-1

)

N-content (%)

77K

InAsN

N reduces electron mobilityµ 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

Electrical properties InAsN on GaAs

A. Patanè et al Appl. Phys Lett. 93, 25106 (2008)

1 10 1000

1

2

3

4

5

H (

m2V

-1s-1

)

1.0%

x=0%

0.2%

0.6%0.4%

T (K)

0.0 0.5 1.01016

1017

nH (

cm-3

)

x (%)

T = 293K

Phonon scattering

impurity scattering

1000 nm n-type InAs(N)

Semi-insulating GaAs substrate

The electron mass and its dependence on the excitation energy are weakly affected by the nitrogen

0.0 0.5 1.0 1.5 2.0

0.025

0.030

0.035

m

e*/m

0

N (%)

11.4 m 15.0 m 66.0 m 103.0 m

O. Drachenko et al. APL 98, 162109 (2011)

Electron Cyclotron Mass

GaAsN LCINS, O’Reilly

CR InAsN

CR/PR GaAsN(m

e)

Comparing the N-induced change of the mass in InAsN and GaAsN

The cyclotron mass increases with increasing x

The increase of electron density with increasing N indicates a pinning of the Fermi level and implies a substantial density of native donor states

InAsN - Cyclotron Resonance

O. Drachenko et al. APL 98, 162109 (2011)

-4x106 0 4x106

0.3

0.4

0.5

2.0%

1.0%

(eV

)

k (cm-1)

N = 0%

EF

Pinning of the Fermi level

0.0 0.5 1.0 1.5 2.01016

1017

1018

n (

cm-3

)

N (%)0.0 0.5 1.0 1.5 2.01016

1017

1018

20 meV

80 meV 40 meV

n (

cm-3

)

N (%)

EF= 10 meV

0 50 100 150 200 250 300

0.325

0.330

0.335

0.340

0.345

0.350

0.355

Ban

d G

ap E

nerg

y (e

V)

Temperature (K)

Eg=0.353-[1.1x10-4T2/(T+100)]

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

J. Appl. Phys. 108, 103504 (2010)

PL is Gaussian at low T As T increases becomes asymmetric with high energy tail extends well above Eg

Lineshape - 2 effectsLocalization at low TFree carrier emission at high T

Photoluminescence Lineshape

0.26 0.28 0.30 0.32 0.34 0.36 0.38 0.40

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

4K 20K 40K 60K 80K100K120K150K180K210K240K270K300K

Inte

nsity

Photon Energy (eV)

Conduction Band

Valence Band

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0.30

0.35

0.40

E0 InAsN/InAs

InAsN/GaAs InAsN/InAs E

0

InAsN/InAs o

BAC model

Ene

rgy

(eV

)

Nitrogen content (%)

0

PL obtained from InAsN on GaAs across the mid-IR spectral range with addition of small quantities (~ 1%) of nitrogen

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

InAsN on GaAs4K PL

improved PL

0 50 100 150 200 250 300

10-2

10-1

100

InAs/InAs InAs/GaAs InAsN(0.6%)/GaAs InAsN(1%)/GaAs

No

rma

lise

d P

L I

nte

nsi

ty (

a.u

.)

Temperature (K)

2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6

0

2

4

6

8

10

Inte

nsity

(a.

u.)

Wavelength (m)

InAs/GaAs

0.2%N

0.4%N

0.6%N

1%N

CO2

Adding Sb - MBE growth of InAsSbN

N is hard to incorporateUse Sb to reduce lattice mismatch increase N incorporation improve quality

InAsConduction band

Valence band

Increasing N

Tensile strain

Increasing Sb

Compressive strain

Adding N to InAs

Adding Sb to InAs

Eg

Sb acts as surfactant to maintain 2D growth and reduces point defects - improves PLRed-shift of emission wavelength – need less N to reach longer wavelengthsSb reduces N surface diffusion length - increases N incorporation ~ 2.5xReduction of Sb segregation induced by N - increases Sb incorporation ~1.5x

0.0 0.5 1.0 1.5 2.0

0.3

0.4

0.5

0.6

0.7

0.8

7.3

% S

b7

.0%

Sb

4.1

% S

b2

.6%

Sb

4.8

% S

b

E

ne

rgy

(eV

)

Nitrogen concentration (%)

E0

E0+SO

SO

Fits for InNAs

(d) In(N)AsSb0.0 0.5 1.0 1.5 2.0

0.3

0.4

0.5

0.6

0.7

0.8

(c) InNAs

This work: Ref.[31]: E0 E0

E0+SO E0+SO

SO SO

Fit

Energ

y (e

V)

Nitrogen concentration (%)

Photoreflectance

Kudrawiec et al. APL 99, 011904 (2011)

Δso > E0 Auger suppression

Advantage of InAsNSb over InAsNIn-plane strain for layers grown on InAscan be tuned from tensile to compressive- Tailor polarization in QW to be either TE or TMSb increases confinement in valence band - dominant polarisation is TE (e1-hh1)

Spin orbit splitting In InNAs & InAsNSb

Incorporation of Sb increases Δso and decreases E0 N does not change Δso

Both Sb and N reduce E0

~ 5 meV per 1% of Sb~ 60 meV per 1% N

InNAs InNAsSb

Strong PL at room temperature - good optical quality Asymmetric shape

Narrow energy gap – free carrier emission is important Especially > 100 KHigh energy tail extends well above Eg

Gaussian at low TPL 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

InAsSbN Photoluminescence

Latwoska et al, Appl. Phys. Lett 102, 122109 (2013)

InAsN QW lasers on InPInAsN ridge lasers operating up to 2.6 µm have been demonstrated – grown by gas source MBElimited 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)

MQW containing 18% N

on GaAs (UNM)- longest wavelength PL obtained from dilute Ngrowth temperature 500 0C

InAsN MQW grown by MOVPE

Osinski , Optoelectronics Review 11(4) 321-6 (2003)

InAsSbN / InAs MQWs

-4000 -3000 -2000 -1000 0 1000 2000 3000 4000100

101

102

103

104

105

106

200 nm InAs Buffer Layer

InAs substrate

100 nm InAs Capping Layer

10x InAsNSb /InAs QW

(12x24 nm)

Growth of the MQWs calibrated using the same growth method of previously grown InAsNSb bulk layers

200 nm InAs Buffer layer grown at 480°C 10x InAsSbN/InAs QW grown at 420°C• Growth rate of 0.5µm per hour• Nitrogen plasma setting fixed at 160 W with flux of 6×10-6 mbar 100 nm InAs Capping Layer grown at 480°C As flux kept at minimum for growth of InAs layers

∆EV = 102meV

hh1 = 9meVhh2 = 36meV

InAs0.92Sb0.08InAs InAs

∆EV = 102meV

hh1 = 9meVhh2 = 36meV

InAs0.92Sb0.08InAs InAs

InAsSbN/InAs MQW 4K photoluminescence

No blue-shift with excitation power - Type I QW

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 Reduction of band gap

• Conduction band further reduced by BAC model Reduction of 63 meV

3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4-1

0

1

2

3

4

5

6

7

2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6

Wavelength (m)

4K

=3.48me

1-lh

1

=3.68me

1-hh

1

Peak Wavelength

tot=3.62m

Re

lativ

e In

ten

sity

(a

.u.)

Wavelength (m)

1.8W 1.6W 1.2W 1W 0.8W 0.6W 0.5W 0.4W 0.2W 0.1W 0.06W 0.03W

e - hh1

e - lh1

2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0-0.001

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

Inte

nsi

ty (

a.u

.)

Wavelength (m)

4.38 m Bulk

3.62 m MQW

4K

3.62 µm (expt.) 3.48 µm

N =1%, Sb 6%

2.5 3.0 3.5 4.0 4.5

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Inte

nsity

(a.

u.)

Wavelength (m)

30mA 50mA 75mA 100mA 150mA

4K

InAsSbN MQW LEDp-i-n diode containing 10xInAsSbN QW in active region N =1%, Sb 6%

Longest wavelength dilute nitridelight emitting device to date

InAs (100) substrate

n InAs

p InAs

2500 3000 3500 4000 45000

10

20

30

40

50

EL

Inte

nsity

(a.u

.)

Wavelength (nm)

25mA 50mA 75mA 100mA 150mA 200mA

C-H absorption

300 K EL

n+-InAs

p+-InAs

InAsNSb MQW

4 K EL

LED output power : 6 µW at 100 mA drive current and internal RT efficiency ~ 1%

InAsSbN e-hh1InAsSb e-hh1InAsSb e-hh2

0 50 100 150 200 250 300

2

4

6

8

10

12

Out

out P

ower

(W

)

Current (mA)

R0A ~1/n

3 4 5 6 7 8 9 10 11 12 13

2

3

4

5

6

7

89

10

R0A

(cm

2 )

1000/T (K-1)

(R0A) 1/n2

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.50.1

1

10

EL

em

issio

n (

a.u

)

Ph

oto

resp

on

se

(a

.u.)

Wavelength (m)

InAsSbN MQW p-i-n photodetector

-0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.350.00E+000

5.00E+016

1.00E+017

1.50E+017

2.00E+017

2.50E+017

3.00E+017

3.50E+017

4.00E+017

A0363

C-2 (

F-2)

Voltage (V)

Vbi=0.19V

1/C2=2(Vbi-V)/A2qN

A

Slope = NA

x-intercept = Vbi

NA = 8.3x1017cm-3

-0.5 0.0 0.5 1.0 1.51E-6

1E-5

1E-4

1E-3

0.01

0.1

Cu

rre

nt (A

)

Voltage (V)

4 K 20K 40K 60K 80K 100K 120K 140K 160K 190K 220K 250K 280K 300K

Cut-off λ ~ 4 μmIdeality factor = 1.6R0A T<120 K generation-recombination dominates T>220K diffusion limited recombination is dominantCapacitance at 0V =2.54 nF Built in potential = 0.19 V Carrier concentration = 8.3x1017 cm-3

R0A ~1/n2

New prospectsRecent 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 intensityIn InAsN

GaAsN +H results in passivation of N which restores the bandgap (reversibly)

Can create GaAsN quantum dots

GaAsN

GaAs

hydrogen

Change to GaInAsN - single photon sourcesMicro – 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 contentFermi 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 spectraN 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 Institute of Physics, Wroclaw Photoreflectance M. Latkowska

O. Drachenko Helmholtz-Zentrum Cyclotron resonance M. Helm Dresden-Rossendorf

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

InAsSbN MQW LEDN =1%, Sb 6%

2400 2600 2800 3000 3200 3400 3600 3800 4000 4200

0.002

0.004

0.006

0.008

0.010

0.012

Inte

nsit

y (a

.u.)

Wavelength (nm)

4K 20K 40K 60K 80K 100K 120K 140K 160K 190K 220K 250K 280K 300K

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

Comparison with InAsSb

InAsSbN e-hh1InAsSb e-hh1InAsSb e-hh2

PL analysis temperature dependence

2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6

0.0

0.2

0.4

0.6

0.8

1.0

Inte

nsity (

a.u

.)

Wavelength (m)

300K

CO2

InAsN(1%) exhibits very weak temperature quenching ~ 8xPL emission obtained up to room temperature without annealing Peak wavelength near 4 µm – appropriate for CO2 detection

2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6-1

0

1

2

3

4

5

6

7

8

A0299

Inte

nsi

ty (

a.u

.)

Wavelength (m)

4K 20K 40K 60K 80K 100K 120K 140K 160K 190K 220K 250K 280K 300K

CO2

InAsN

X-valley

L-valley

<100> <111>

G-valley

Energy

Wave vector

Eg-G = 0.35 eV EL=1.08 eV EX=1.37 eV

N

GaAsN

X-valley

L-valley

<100> <111>

G-valley

Energy

N

Eg-G = 1.42 eV EL~0.3 eV EX~0.3 eV

Comparing III-N-Vs

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).

0 20 40 600

1

0 20 40

15.0m = 66.0m

11.4m

x = 1.1%

1.9%

1.1 %

Tra

nsm

issi

on

B(T)

= 11.4 µmT = 4.2K

N = 0%N = 0%

N = 1.1%

Patanè et al. PRB 80 115207 (2009)

0 2 4 6 8 10

Tra

nsm

issi

on (

arb.

unit

s)

B (T)

c*e 2/eBm

ee mm 025.0*

ee mm 027.0*

ee mm 060.0*

ps15.0~e

ps10.e

x=0%

0.4%

1.0%

ee mm 029.0*

ps1.0~e

0.6%

T =100 Ku= 2.9THz

ps20.0~e

InAs1-xNx

InAsN - Cyclotron ResonanceMagneto-transmission in pulsed magnetic field B up to 60T and monochromatic excitation by QCL

Minimum at the resonance field Bc gives me* = eBCl/(2pc)

Area of the CR minimum gives electron density n

CR quenches in GaAsN (0.1%) due to low μ

Photoreflectance Spectroscopy

PR spectra can be fitted using

where C and θ are amplitude and phasem=2.5 for b-b

InAsN on InAs

InAsN

X-valley

L-valley

<100> <111>

G-valley

Energy

Wave vector

Eg-G = 0.35 eV EL=1.08 eV EX=1.37 eV

N

GaAsN

X-valley

L-valley

<100> <111>

G-valley

Energy

N

Eg-G = 1.42 eV EL~0.3 eV EX~0.3 eV

Avalanche photodiodes

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 IonizationRapid increase of current at large electric fields (>1kV/cm) due to impact ionization (IO).

-4 -2 0 2 4

-0.1

0.0

0.1

0 2 40.00

0.06

x=0.6%L=2m

5m10m

0 2 40.00

0.05

x=0%

10m

5m

L=2m

x =0.6%

x =0%

L = 10mW = 5m

I (A

)

V (V)

T=77K2mm

I

Makarovsky et al., APL 96, 052115 (2010)

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

Dilute nitrides

Harris, J. S. Semiconductor Science and Technology 17, 880 (2002)

N introduces tensile strain (on InAs or GaAs)disorder and strong bowing

D. Sentosa, X. Tang,a, and S.J. Chua, Eur. Phys. J. Appl. Phys. 40, 247–251 (2007)

N

InAs InN

InAsN Photoreflectance

Where, x is the N content

Solid lines are fits to

N does not change Δso

Fit using

Includes localized and band-band transitionsA = scaling factorEcr = energy of crossover between equationsK = smoothing parameterσ 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

Best fit when n=1Black arrows – Eg determined from PL fittingRed arrows – PL peak

Note the difference which increases with T

Photoluminescence curve fitting

Latwoska et al, Appl. Phys. Lett 102, 122109 (2013)

Temperature dependence

Bose-Einstein formula

Eg obtained from PLspectral fittingdeviates from PL peak value especially at T> 80K

Free carrier emission must be taken into account

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

Comparison of change in energy gap with TInNAsSb 65 meVInAs 66 meVInSb 62 meV

whereas 1% N in GaAs reduces T dependence of Eg by 40%

Temperature dependence of bandgap

BAC model gives good agreement

T dependence of Eg in InNAsSb is notsensitive to N due to large separation between EN and EM (~ 1 eV)

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