Unusual compositional dependence of the Unusual compositional - - PowerPoint PPT Presentation

Unusual compositional dependence of the it d d Unusual compositional dependence of the it d d exciton reduced mass in GaAs1 xBix (x=0‐10%) exciton reduced mass in GaAs1 xBix (x=0‐10%)

1‐x x (

)

1‐x x (

)

G Pettinari1 A Polimeni2 J H Blokland1 R Trotta2

• G. Pettinari1, A. Polimeni2, J. H. Blokland1, R. Trotta2,
• P. C. M. Christianen1, M. Capizzi2, J. C. Maan1,

X Lu3 E C Young3 and T Tiedje3

• X. Lu , E. C. Young and T. Tiedje

1High Field Magnet Laboratory,

Radboud University Nijmegen, The Netherlands

2Dipartimento di Fisica,

Sapienza Università di Roma, Italy Radboud University Nijmegen, The Netherlands

3Department of Physics and Astronomy,

University of British Columbia, Vancouver, Canada

Ann Arbor, July 16th

Outline

Bismuth in GaAs: ‐ electronic properties ‐ magneto‐photoluminescence (0‐30 T) and exciton reduced mass determination exciton reduced mass determination ‐ evidence for a largely perturbed band structure ‐ evidence for a largely perturbed band structure

Ga(As,Bi) expected trends

electronegativity atomic electron electronegativity first ionization potential V

6p Bi 4p As CBs

Bi is expected to

number

III B V B

configuration

2s N 4s Ga p s VBs

influence the valence band

B N

3.04 14.5

1s22s2p3

Al P

2.18 1.81

Large relativistic corrections are expected due to Z →

Ga As

9.81

[Ar]3d104s2p3

.8 6.00

[Ar]3d104s2p1

expected due to ZBi → large SO splitting ∆0 of VB anion p‐states ∆ (G Bi) 2 15 V

In Sb Tl Bi

2.02 7.29

∆0(GaBi)=2.15 eV

Tl Bi

[Xe]4f145d106s2p3

• P. Carrier and S.‐H. Wei, Phys. Rev. B 70, 035212 (2004)

Ga(As,Bi) expected trends

Predicted E = ‐1 45 eV for GaBi

• A. Janotti, S.‐H. Wei, and S. B. Zhang, Phys. Rev. B 65, 115203 (2002)

GaBi

Predicted Eg= ‐1.45 eV for GaBi

density functional formalism and LDA (64‐atom cell calculation)

Expected band gap reduction following (heavier anion)‐(smaller gap) rule

L X Γ

(heavier anion) (smaller gap) rule

EBi VBM

• Y. Zhang, A. Mascarenhas, and L. –W. Wang, Phys. Rev. B 71, 155201 (2005)

L li ti f l b d t t t Bi

EBi VBM

• Localization of valence band states at Bi

atoms

• Bi generates an impurity state (EBi) 80 meV

below the VBM

• Pressure coefficient of EBi similar to GaAs,

no Bi state emerging from the VB

density functional formalism and LDA

Ga(As,Bi) observed trends

1.20 1.40 (eV) GaAs1-xBix T=290 K

4 . 10 eV 5 . 9 eV 36 . ) 1 ( ) ( ) 1 ( ) 1 (

GaBi GaAs GaBi Bi GaAs1

= = − = + = − − − + =

−

β α β α E x x b x x E x E x E

x x

b

Kunishige Oe and Hiroshi Okamoto, Jpn. J. Appl. Phys. 37, L1283 (1998)

• X. Lu et al., Appl. Phys. Lett. 95, 41903 (2009)

1.00 Energy

experiment (PL)

x=(0‐5)% ∆Eg≈‐80 meV/%Bi

(GaAs1‐xNx; ∆Eg≈-100 meV/%N; b~16-20 eV)

• X. Lu et al., Appl. Phys. Lett. 95, 41903 (2009)

0.800 2 4 6 8 10 12 x (%)

experiment (PL)

1.44

A larger band gap reduction is observed for the same increase in lattice constant

1.28 y (eV) InzGa1-zAs GaAs N

Potential for

0 96 1.12 nd gap Energ GaAs1-yNy

z =24% y=5%

GaAs1-wSbw

w=22%

GaAs Bi

1 31 µm

• Heterojunction bipolar transistors
• Solar cells
• Telecom

0.8 0.96 5 6 5 65 5 7 5 75 Ban

x=10% GaAs

GaAs1-xBix

1.31 µm 1.55 µm

5.6 5.65 5.7 5.75 a (Å)

Ga(As,Bi) observed trends

• B. Fluegel et al., Phys. Rev. Lett. 97, 067205 (2006)

eV 34 eV 15 2 ) 1 ( ) 1 ( ) Bi GaAs (

GaAs GaBi GaAs GaBi 1

= ∆ = ∆ − − ∆ − + ∆ = ∆

−

x x x x

x x

b eV 34 . eV 15 . 2 ∆ ∆

b = ‐6.0 eV

(GaAs1‐xNx; ∆0 constant)

Potential for spintronics Bi‐related states form with pressure coefficient similar to GaAs Ultrafast photoresponse in the NIR for emitters and detectors of pulsed THz radiation

• K. Bertulis et al., Appl. Phys. Lett. 88, 201112 (2006)
• S. Francoeur et al., Phys. Rev. B 77, 085209 (2008)

Ga(As,Bi): what about the carrier mass?

• J. Wu et al., J. Appl. Phys. 105, 011101 (2009)
• R. N. Kini et al., J. Appl. Phys., 106, 043705 (2009)

Bi incorporation affects the electron mobility

We address the carrier effective mass in Ga(As,Bi) b t h t l i by magneto‐photoluminescence

The samples

Grown on (100) GaAs by molecular beam epitaxy Grown on (100) GaAs by molecular beam epitaxy x =0, 0.6, 1.3, 1.7, 1.9, 3.0, 3.8, 4 5 5 6 8 5 and 10 6%

GaAs1-xBix T = 200 K

FE 8 % x = 10.6%

4.5, 5.6, 8.5 and 10.6% TG=(270 – 380) °C, thickness t=(40‐350) nm

x = 8.5% x = 5.6%

• X. Lu et al., Appl. Phys. Lett. 92, 192110 (2008)
• b. units)

x = 3 8% x = 4.5%

ensity (arb

x = 3% x = 3.8%

PL Inte

x = 1.9% x = 1.7%

d l

x = 1.3% x = 0.6%

LE

Good structural properties

0.8 1.0 1.2 1.4 Energy (eV)

The samples

Grown on (100) GaAs by molecular beam epitaxy Grown on (100) GaAs by molecular beam epitaxy x =0, 0.6, 1.3, 1.7, 1.9, 3.0, 3.8, 4 5 5 6 8 5 and 10 6%

GaAs1-xBix T = 200 K

FE 8 % x = 10.6%

4.5, 5.6, 8.5 and 10.6% TG=(270 – 380) °C, thickness t=(40‐350) nm

x = 8.5% x = 5.6%

• b. units)

x = 3 8% x = 4.5%

110

ensity (arb

x = 3% x = 3.8%

90 110 M (meV)

T=200 K

PL Inte

x = 1.9% x = 1.7%

70 FWHM

x = 1.3% x = 0.6%

LE

50 2 4 6 8 10 x (%)

Unusual compositional linewidth dependence

0.8 1.0 1.2 1.4 Energy (eV)

Unusual compositional linewidth dependence

High‐magnetic field measurements

Nijmegen The Netherlands

B = 0 – 33 T

‐ Powered by 2×10 MW at 500 V (4⋅104 A) ‐ Chilled by 104 l/min deionised water at 30 atm at 10 °C.

1 hour magnet time costs 1,000 €

Why 200 K?

GaAs1-xBix x=1.9% T=210 K

FE

GaAs1-xBix x=8.5%

FE

nits) x 1.9%

P=12 P0

nits) x 8.5% T = 200 K

P=20 P

nsity (arb. un

P=P0 P= 4 P0

nsity (arb. un

LE

P= P P= 2 P0 P= 10 P0 P=20 P0

PL Inten

LE

P 12 P

T=10 K PL Inten T = 10 K

P=20 P0 P= 4 P0 P=12 P0 P= P0 P= P0 P= 2 P0 P= 10 P0

1.15 1.2 1.25 1.3 1.35 1.4 Energy (eV) 0.8 0.85 0.9 0.95 1 1.05 Energy (eV)

Localized excitons dominate low‐T photoluminescence p

• G. Pettinari et al., Appl. Phys. Lett. 92, 262105 (2008)

Why 200 K?

units)

GaAs1-xBix - x = 0.6% P0 = 8 W/cm2 (a) GaAs1-xBix - x = 5% P0 = 8 W/cm2 (c) (3.6%) GaAs1-xBix - x = 1.9% P0 = 8 W/cm2 (b)

4.5%

ensity (arb.

FE LE

T = 180 K

16×P0 3×P0 P0 FE

T = 180

16×P0 3×P0 P0 FE

T = 180 K

16×P0 3×P0 P0

K

16×P0

ized PL Inte

FE GaAs 16×P0 16×P0

Normali

FE LE

T = 150 K

3×P0 P0 0.25×P0 FE LE

T = 150

3×P0 P0 0.25×P0 FE LE

T = 150 K

3×P0 P0 0.05×P0

K 1.2 1.3 1.4 1.5

Energy (eV)

1.0 1.1 1.2 1.3

Energy (eV)

1.0 1.1 1.2 1.3 1.4

Energy (eV)

Accurate choice of measurement power and temperature p p

Why 200 K?

S I h f l A l Ph L 96 131115 (2010) R K d i l J A l Ph 106 023518 (2009)

• S. Imhof et al., Appl. Phys. Lett. 96, 131115 (2010)
• R. Kudrawiec et al., J. Appl. Phys. 106, 023518 (2009)

x=3% x=4.5%

Magneto‐PL: data

30 T

GaAs1-xBix x=8.5% T=190 K P=10 W/cm

2

30 T

GaAs1-xBix x=8.5% T=190 K P=70 W/cm

2

At high power carrier scattering disrupts

30 T

• b. un.)

30 T

g p the coherence of the electron/hole cyclotron orbit

ntensity (arb

cyclotron orbit

PL In

0.80 0.85 0.90 0.95 1.00 1.05

0 T

Energy (eV)

0.80 0.85 0.90 0.95 1.00 1.05

0 T

Energ (eV) Energy (eV) Energy (eV) G Pettinari et al Phys Rev B 81 235211 (2010)

• G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)

Magneto‐PL: data

0.95 P0 = ~10 W/cm

2

3×P0

At high power carrier scattering disrupts

0.94 Energy (eV) 7×P0 15×P0

g p the coherence of the electron/hole cyclotron orbit

0.93 PL Peak E T = 190 K

cyclotron orbit

0.92 6 12 18 24 30 B (T) T 190 K GaAs1-xBix- x = 8.5% B (T)

G Pettinari et al Phys Rev B 81 235211 (2010)

• G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)

Magneto‐PL: data

At high power carrier scattering disrupts

T=5 K GaAs:Si n

Si=1018 cm-3

(e,A) bb

g p the coherence of the electron/hole cyclotron orbit

22T 24T 26T 28T 30T

units)

cyclotron orbit as found in degenerate GaAs and InN

14T 16T 18T 20T 22T

tensity (arb. u

and InN

06T 08T 10T 12T

PL Int

1.54

µ = 0.049 m0

1.42 1.46 1.5 1.54 1.58 Energy (eV)

00T 02T 04T

1.52 1.53 ergy (eV) LL0 (e,A)

Energy (eV)

1.51 Ene

me = 0.069 m0 G Pettinari et al Phys Rev B 79 165207 (2009)

10 20 30 B (T)

• G. Pettinari et al., Phys. Rev. B 79, 165207 (2009)

Magneto‐PL: data

At high power carrier scattering disrupts

30T InN n=4×10

17 cm

• 3

T = 5K

g p the coherence of the electron/hole cyclotron orbit cyclotron orbit as found in degenerate GaAs and InN and InN

08T 10T

682

02T 04T 06T

678 ergy (meV) µ = 0.093 m0

600 620 640 660 680 700 720 Energy(meV)

00T

670 674 Ene

• G. Pettinari et al., Phys. Rev. B 79, 165207 (2009)

8 16 24 32 B (T)

Magneto‐PL: data

GaAs1-xBix - x = 0.6% T = 200 K

15

GaAs1 Bi

. . . back to GaAsBi

units)

B = 30 T

10 15

1-x x

x = 0.6% T = 200 K

free exciton

sity (arb. u

27 T 24 T 21 T 18 T

5 10 Ed (meV)

PL Inten

FE 15 T 12 T 09 T 06 T

5 ∆E

localized exciton

1.2 1.3 1.4 1.5 E ( V)

FE FE GaAs LE 03 T 00 T

6 12 18 24 30 B (T)

Energy (eV)

Localized excitons behave differently

Magneto‐PL: analysis

B i d d hif f i b

2

B‐induced shift of given by

(see D. Cabib, E. Fabri, and G. Fiorio, Il Nuovo Cimento 10B, 185 (1972))

∑

= ∆

5 * exc)

; (

i i d

c R B E γ µ

0 048

20 P0 = ~10 W/cm

2

3×P 7×P0

) 2 ( ) (

* excR

B e µ γ h = R* Rydberg

∑

=1 exc)

; (

i i d

γ µ

• µ

exc = 0.048 m

• µ

exc = 0.049 m

• µ

exc = 0.050 m

10 ∆Ed (meV) 15×P0

R Rydberg

exc

• µ

exc = 0.049 m

∆ T = 190 K

• 10

6 12 18 24 30 B (T) GaAs1-xBix- x = 8.5% ( )

The exciton reduced mass does not depend on excitation power

Magneto‐PL: analysis

High‐temperature PL: free‐exciton or free‐carrier ?

18

T 185 K GaAs Free‐exciton: quadratic‐like

12 18

T = 185 K Free‐carrier: Landau levels form

6 Ed (meV) µexc = 0.059 m0 A bl ∆E µ = 0 073 m A more reasonable carrier reduced mass is found for exciton-like recombination 6 12 18 24 30 B (T) µLL 0.073 m0 recombination

Magneto‐PL: analysis

High‐ temperature PL: free‐exciton or free‐carrier ?

15 10 15 meV)

60×P0 - µexc = 0.072 m0 P0 = 5 mW - µexc = 0.071 m0

(a) 10 15

P0 = 50 mW - µexc = 0.079 m 2×P

0 - µ exc = 0.080 m

(b) meV) 5 5 ∆Ed (m

T = 200 K GaAs1 Bi - x = 1.7%

5

T = 200 K GaAs Bi - x = 3%

∆Ed (m

15

GaAs

1 xBi x

• 5

6 12 18 24 30 B (T)

1-x x

6 12 18 24 30 B (T)

GaAs1-xBix x 3%

10 15

µ = 0.077 m0

(meV)

1-x x

x = 5.6% T = 200 K P = 150 mW

5 ∆Ed

T = 220 K µ = 0.081 m0 P = 200 mW

6 12 18 24 30 B (T)

Magneto‐PL: results

30 T = 200 K x = 10.6% GaAs

1-xBi x

GaAs 8.5%

Non monotonic dependence of the

20

d (meV)

0.6% 1.7%

dependence of the exciton reduced mass on Bi concentration

10 ∆Ed 4.5% 12 18 24 30 B (T)

• G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)

Magneto‐PL: results

20 30

GaAs

x = 0.6%

GaAs1-xBix T = 200 K

x = 1.3% x = 1.7%

10 30 10 20 30

x = 3.0% x = 3.8% x = 4.5%

∆Ed (meV)

20 30 x = 5.6%

x = 8.5% x = 10.6%

∆

12 18 24 30 10 20 12 18 24 30 12 18 24 30 12 18 24 30 12 18 24 30 12 18 24 30

B (T) B (T) B (T)

• G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)

Exciton reduced mass

0.08 GaAs1-xBix

Non conventional compositional dependence

m0 )

compositional dependence

k⋅p

followed by a k⋅p‐like behavior

0.06 µexc (m

behavior

0.04 2 4 6 8 10 x (%)

me∝m0(1+P2/Eg)‐1

E *

e 0(

/ g) mhh∝m0(2Q2/E *‐1)‐1

P2=28.9 eV, Q2=8 eV

Eg

, Q

• G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)

• R. N. Kini et al., J. Appl. Phys., 106, 043705 (2009)

Exciton reduced mass: what we learn

0.08 GaAs1-xBix 0 06 (m0 ) 0.06 µexc 0.04 2 4 6 8 10 x (%)

2500

x (%)

Consistent with mobility data

1500 2000 2500 m2V-1s-1)

Consistent with mobility data ∆µ/µ ≈ ∆m/m ≈ 30%

1000 1500

A/µexc mobility

µ (cm 500 0.8 1.6 2.4

mobility

x (%)

Exciton reduced mass: what we learn Exciton reduced mass: what we learn

The unexpected increase of the carrier p mass indicates a highly perturbed band structure.

0.08 GaAs1-xBix

The plateau value (0.08 m0) is not

0 06 (m0 )

conceivable with a perturbation exerting on the VB only. 1/µexc=1/me+1/mh

0.06 µexc

mh→∞, µexc=0.067 m0 The CB has to be perturbed, too The CB has to be perturbed, too

• G. Ciatto et al., Phys. Rev. B 78, 035325 (2008)

0.04 2 4 6 8 10 x (%)

, y , ( )

x (%)

Tendency to Bi atom clustering

x=2.4%

Tendency to Bi atom clustering may perturb CB structure

• G. Pettinari et al., Phys. Rev. B 81, 235211 (2010)

. . . alternatively

h l l ( ) bl

0.08 GaAs1-xBix

The plateau value (0.08 m0) is not conceivable with a perturbation exerting on the VB only. The CB has to be perturbed, too → 0 067

0.06 µexc (m0 )

mh→∞, µexc=0.067 m0

Bi is assumed to substitute As (valence 5) But Bi is usually trivalent due to large

0.04 2 4 6 8 10

But, Bi is usually trivalent due to large separation between 6s2 and 6p3 electrons

(A. Zunger, private communication)

A rather strong tendency of Bi to

2 4 6 8 10 x (%)

A rather strong tendency of Bi to substitute for Ga could be expected

G Ga Bi Ga As Bi As Bi

In fact, . . .

Exciton reduced mass: what we learn

Exciton reduced mass: what we learn Exciton reduced mass: what we learn

M Kunzer et al Phys Rev B 48 4437 (1993)

• M. Kunzer et al., Phys. Rev. B 48, 4437 (1993)

Ga A Bi Ga Bi

Then, what CB structure is expected for

As As

is expected for (GaBi)As?

Exciton reduced mass: what we learn

0.08 k⋅p GaAs1-xBix

The recovery of a conventional‐ alloy behaviour above x>8% i t t d t ti f

0.06

exc (m0 )

points toward a restoration of a random atomic distribution of Bi atoms

0 04 µe

atoms.

0.04 2 4 6 8 10 x (%)

• A. Lindsay et al., Phys. Rev. B 77, 165205 (2008)

2 3

i=1 i=2 i=3 i=4

m*

host

InSbN GaSbN

1 2 m*

alloy/m

00 1 2 3 4 x, nitrogen concentration (%)

• G. Ciatto et al., private communication

Exciton reduced mass: what we learn

0.08 k⋅p GaAs1-xBix

The recovery of a conventional‐ alloy behaviour above x>8% i t t d t ti f

0.06

exc (m0 )

points toward a restoration of a random atomic distribution of Bi atoms

0 04 µe

atoms.

0.04 2 4 6 8 10 x (%)

90 110 M (meV)

PL linewidth

50 70 FWHM 50 2 4 6 8 10 x (%)

• G. Ciatto et al., private communication

Exciton reduced mass: what we learn

0.08 k⋅p GaAs1-xBix

Alternatively, the formation of Bi antisites is less likely above a t i Bi t ti

0.06

exc (m0 )

certain Bi concentration

0 04 µe 0.04 2 4 6 8 10 x (%)

G Ga Bi Ga As Bi As Bi

Conclusions

The peculiar dependence of the exciton reduced mass reveals an transition of the nature of the band extrema from impurity like to transition of the nature of the band extrema from impurity‐like to band‐like. The compositional dependence of the carrier effective mass mirrors major changes occurring in the structural properties of the lattice: ‐ disorder to order transition formation of Bi antisites highlighting the competing ‐ formation of BiGa antisites highlighting the competing characteristics of Bi as a metal and a group V element The decrease in the carrier effective mass for x>8% turns out to be

• f particular interest in all those applications where carrier
• f particular interest in all those applications where carrier

mobility is a relevant issue.