Temperature Dependent Hole Mobility in MBE grown GaAs 1 x Bi x D.A. - - PowerPoint PPT Presentation

Temperature Dependent Hole Mobility in MBE grown GaAs1−xBix

D.A. Beaton, R.B. Lewis, M. Masnadi-Shirazi and T. Tiedje dan.beaton@gmail.com Univ. of British Columbia, Vancouver, Canada

• Univ. of Victoria, Vancouver, Canada
• Sample growth and fabrication
• Growth conditions and hole mobility
• GaAs1−xBix hole mobility
• Temperature dependence

Bismuth Containing Semiconductors Workshop 2010 – p. 1

N and Bi in GaAs

• Nitrogen perturbs the conduction band and

reduces electron mobility

• Expect Bismuth to perturb valence band and

effect hole mobility

Bismuth Containing Semiconductors Workshop 2010 – p. 2

MBE Growth of GaAs1−xBix

GaAs buffer

• Tgrow ≃ 580◦C
• As:Ga ratio ≃ 8
• Growth rate ≃ 1 µm/hr
• Ga BEP ≃ 2x10−7 Torr

GaAsBi

• Tgrow ≃ 350◦C
• Growth rate ≃ 0.1 µm/hr
• As:Ga ratio ≃ 1 − 2.0
• Bi BEP ≃ 5x10−10 Torr

GaAs1−xBix GaAs buffer 500-1000 nm SI GaAs (001) Substrate G.I.

Bismuth Containing Semiconductors Workshop 2010 – p. 3

MBE Growth

• Effusion cells for Ga, Bi
• Valved two-zone cracker

for As2

• Carbon dopant from

CBr4 flow controlled gas source

• In-situ:

Band gap ther- mometry, RHEED, Light scattering VG-80H MBE Chamber

Bismuth Containing Semiconductors Workshop 2010 – p. 4

Hall Measurements

• Thicknesses 250 − 1000 nm
• Doping: 8x1016-2x1018cm−3
• Depletion widths=70-20nm
• 7 × 7 mm squares
• Ti/Pt/Au Ohmic contacts
• Van der Pauw method
• B = 0.265 T
• Temperatures of 25-300 K

Bismuth Containing Semiconductors Workshop 2010 – p. 5

Hole Mobility of p-GaAs

1017 1018 Hole concentration (cm-3) 102 µh (cm2V-1s-1) 1017 1018 Hole concentration (cm-3) 102 µh (cm2V-1s-1) conventional growth Low T Low T, low As:Ga Low T, low As:Ga w/Bi From Adachi, 2005

• Low temperature growth of GaAs with Bi

surfactant shows no reduction in hole mobility

Bismuth Containing Semiconductors Workshop 2010 – p. 6

Hole Mobility of p-GaAs1−xBix

1 2 3 4 5 6 x (%) 101 102 µh (cm2V-1s-1) Low T, low As:Ga GaAs w/Bi GaAsBi 102 103 µe (cm2V-1s-1) GaNAs, µe

• Hole mobility decreases with increasing [Bi]
• Effect weaker than N incorporation on electron

mobility

Bismuth Containing Semiconductors Workshop 2010 – p. 7

Mobility Temp. Dep.

• Contributions from phonons, ionized impurities

and Bi incorporation 1 µ = 1 CphT 1.5 + T 1.5 CI + 1 CBi

• Kinetic Theory;

1 NBiσ = v m∗CBi q

• Fahy et al. 1; σ =

1 16π

m∗

2

2

dEg dx

2 a6 a is GaAs lattice parameter, dEg

dx = 8.8 eV

→ σ = 2.0 nm2

1 S. Fahy, A. Lindsay and E.P. O’Reilly, IEE Proc. Optoelectron. 151, 352 (2004) Bismuth Containing Semiconductors Workshop 2010 – p. 8

Mobility Temp. Dep. in GaAs

Tgrow = 350◦C ; As:Ga≃ 2 ; w/ Bi surfactant

102 103 µ, cm2/V s 50 100 150 200 250 300 Temperature, K 102 103 µ, cm2/V s r2208, GaAs µ(T) T-1.5 T1.5

• Bismide-like growth conditions, GaAs1−xBix

x= 0

• Will use Cph from this sample for GaAs1−xBix

samples

Bismuth Containing Semiconductors Workshop 2010 – p. 9

Mobility Temp. Dep. in GaAs1−xBix

100 200 300 Temperature (K) 101 102 µh (cm2/V s) GaAs 0.94% 1.95% 3.50% 5.5%

• Increasing effect from CBi with increasing [Bi]

Bismuth Containing Semiconductors Workshop 2010 – p. 10

Mobility Temp. Dep. in GaAs1−xBix

[Bi] (%) 0% 0.94% 1.95% 3.5% 5.5% µ(300K)

• cm2

V s

• 200

88 100 60 8 Cph 1.0×106 1.0×106 1.0×106 1.0×106

• CI

0.9 0.28 0.28 0.28 0.28 CBi

• 330

570 130 9

⇓ ⇓

isolated Bi, σBi = 0.2 nm2 2.0 nm2

Bismuth Containing Semiconductors Workshop 2010 – p. 11

Conclusions

• Low temperature growth of GaAs with Bi

surfactant shows no reduction in hole mobility

• Decreasing hole mobility for increasing [Bi] in

GaAs1−xBix up to x= 5.5%

• Weaker effect than decreasing electron mobility

in GaNxAs1−x

• Effect of Bi modeled with temperature

independent term

• Estimated σ = 0.2-2.0 nm2

Bismuth Containing Semiconductors Workshop 2010 – p. 12

Conclusions

• Low temperature growth of GaAs with Bi

surfactant shows no reduction in hole mobility

• Decreasing hole mobility for increasing [Bi] in

GaAs1−xBix up to x= 5.5%

• Weaker effect than decreasing electron mobility

in GaNxAs1−x

• Effect of Bi modeled with temperature

independent term

• Estimated σ = 0.2-2.0 nm2

Thank you

Bismuth Containing Semiconductors Workshop 2010 – p. 12