Perpendicular transport across (Al,Ga)As and the Γ to X transition

Tunneling (TU) and thermionic emission (TE) through GaAs/AlxGa1-xAs/GaAs structures was studied in the (001) direction, as a function of AlAs mole fraction x, from x=0.3 to x=0.8. Barrier heights deduced for TU and TE were the same, with a broad peak of 0.35eV for 0.4<x<0.5. Pre-factors for TU and TE were in reasonable agreement with theory for x<0.5 but dropped rapidly for larger x. The effective mass ratio for TU was Γ like for x<0.4 and increased to ≅0.2 for x > 0.5. These data suggest that TU transport is via the transverse X valleys for large x and the low pre-factors for both TU and TE indicate reflections at this boundary caused by wave-function mismatch. These data are also directly applicable to the design and optimization of heterojunction transistors. © 1986.