Г-L intervalley separation and electron mobility in GaAsSb grown on InP: Transport comparison with the GaInAs and GaInAsSb alloys

Abstract

GaAs 0.51 Sb 0.49 is lattice-matched to InP and finds electron transport applications in base or absorber layers in high-speed heterostructure bipolar transistors or photodiodes, because its staggered ("type-II") band alignment with InP favors electron injection across abrupt heterojunctions. Little remains known about electron transport properties and band structure details of GaAs x Sb 1Àx near x ¼ 0.5. Particularly, based on the C-L intervalley separation in binary constituents (D CL ¼ 84 meV in GaSb and 290 meV in GaAs at 300 K), interpolation suggests a low C-L separation in GaAs 0.51 Sb 0.49 before considering energy gap bowing effects. To gain insight into electron transport in GaAs 0.51 Sb 0.49 , we characterized experimental Hall electron mobilities vs carrier concentration at 300 and 77 K in n-type GaAs 0.51 Sb 0.49 , Ga 0.47 In 0.53 As, and Ga 0.76 In 0.24 As 0.67 Sb 0.33 alloys nearly matched to InP. In marked contrast to the other two alloys, GaAs 0.51 Sb 0.49 exhibits a sharp rise in 77 K electron mobility, which evidences L-valley de-population for lower electron concentrations. A two-band transport analysis reveals a C-L valley separation D CL ¼ 91 meV at 77 K, significantly lower than values recommended in the literature. Based on the reported temperature variations of D CL in GaAs and GaSb, 84 < D CL < 95 meV is expected at 300 K. The corresponding GaAs x Sb 1Àx L-valley bowing parameter is c L ¼ 1.63 eV, significantly higher than the 1.1-1.2 eV recommended in the literature. In contrast to GaAs x Sb 1Àx , GaInAsSb grown on InP displays a strong alloy scattering, which limits its low-temperature electron mobility.

High Power InP/Ga(In)AsSb DHBTs for Millimeter-Wave PAs: 14.5 dBm Output Power and 10.4 mw/μm2 Power Density at 94 GHz

“…The base transport properties of InP/GaAsSb DHBTs can be improved by adding In-to the GaAsSb alloy to form a quaternary GaInAsSb base with an increased -L valley separation. Recent work demonstrated that GaInAsSb indeed shows higher 300 K electron mobilities than GaAsSb at a given electron concentration [12]. The use of a compositionally graded GaInAsSb base in DHBTs was shown to improve electron injection efficiency into the InP collector [13].…”