Temperature Dependent Hole Mobility in MBE grown GaAs 1 − x Bi x 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 • GaAs 1 − x Bi x 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 GaAs 1 − x Bi x GaAs buffer • T grow ≃ 580 ◦ C GaAs 1 − x Bi x G.I. • As:Ga ratio ≃ 8 GaAs buffer • Growth rate ≃ 1 µ m/hr 500 - 1000 nm • Ga BEP ≃ 2 x 10 − 7 Torr GaAsBi SI GaAs • T grow ≃ 350 ◦ C (001) Substrate • Growth rate ≃ 0 . 1 µ m/hr • As:Ga ratio ≃ 1 − 2 . 0 • Bi BEP ≃ 5 x 10 − 10 Torr Bismuth Containing Semiconductors Workshop 2010 – p. 3
MBE Growth • Effusion cells for Ga, Bi • Valved two-zone cracker for As 2 • Carbon dopant from CBr 4 flow controlled gas source • In-situ : Band gap ther- VG-80H MBE mometry, RHEED, Light Chamber scattering Bismuth Containing Semiconductors Workshop 2010 – p. 4
Hall Measurements • Thicknesses 250 − 1000 nm • Doping: 8 x 10 16 - 2 x 10 18 cm − 3 • Depletion widths= 70 - 20 nm • 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 µ h ( cm 2 V - 1 s - 1 ) µ h ( cm 2 V - 1 s - 1 ) 10 2 10 2 conventional growth Low T Low T, low As:Ga Low T, low As:Ga w/Bi From Adachi, 2005 10 17 10 17 10 18 10 18 Hole concentration (cm - 3 ) Hole concentration (cm - 3 ) • 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-GaAs 1 − x Bi x Low T, low As:Ga GaAs w/Bi GaAsBi 10 2 10 3 µ e (cm 2 V - 1 s - 1 ) µ h ( cm 2 V - 1 s - 1 ) GaNAs, µ e 10 1 10 2 0 1 2 3 4 5 6 x (%) • 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 C ph T 1 . 5 + T 1 . 5 1 1 + 1 µ = C I C Bi N Bi σ = v m ∗ C Bi 1 • Kinetic Theory; q � 2 � 2 � dE g • Fahy et al. 1 ; σ = 1 � m ∗ a 6 16 π � 2 d x a is GaAs lattice parameter, dE g d x = 8 . 8 eV → σ = 2 . 0 nm 2 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 T grow = 350 ◦ C ; As:Ga ≃ 2 ; w/ Bi surfactant 10 3 10 3 T 1.5 µ , cm 2 /V s µ , cm 2 /V s T - 1.5 r2208, GaAs µ ( T ) 10 2 10 2 50 100 150 200 250 300 Temperature, K • Bismide-like growth conditions, GaAs 1 − x Bi x x = 0 • Will use C ph from this sample for GaAs 1 − x Bi x samples Bismuth Containing Semiconductors Workshop 2010 – p. 9
Mobility Temp. Dep. in GaAs 1 − x Bi x GaAs 1.95% 0.94% 10 2 µ h (cm 2 /V s) 3.50% 5.5% 10 1 0 100 200 300 Temperature (K) • Increasing effect from C Bi with increasing [Bi] Bismuth Containing Semiconductors Workshop 2010 – p. 10
Mobility Temp. Dep. in GaAs 1 − x Bi x [Bi] (%) 0% 0.94% 1.95% 3.5% 5.5% � � cm 2 µ (300 K ) 200 88 100 60 8 V s 1.0 × 10 6 1.0 × 10 6 1.0 × 10 6 1.0 × 10 6 C ph - C I 0.9 0.28 0.28 0.28 0.28 C Bi - 330 570 130 9 ⇓ ⇓ isolated Bi, σ Bi = 0 . 2 nm 2 2 . 0 nm 2 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 GaAs 1 − x Bi x up to x = 5 . 5 % • Weaker effect than decreasing electron mobility in GaN x As 1 − x • Effect of Bi modeled with temperature independent term • Estimated σ = 0 . 2 - 2 . 0 nm 2 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 GaAs 1 − x Bi x up to x = 5 . 5 % • Weaker effect than decreasing electron mobility in GaN x As 1 − x • Effect of Bi modeled with temperature independent term • Estimated σ = 0 . 2 - 2 . 0 nm 2 Thank you Bismuth Containing Semiconductors Workshop 2010 – p. 12
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