PERPENDICULAR TRANSPORT ACROSS (AL,GA) AS AND THE GAMMA-TRANSITION TO X-TRANSITION

Tunneling (TU) and thermionic emission (TE) through GaAs/Al//xGa//1// minus //xAs/GaAs structures was studied in the 001 direction, as a function of AlAs mole fraction x, from x equals 0. 3 to x equals 0. 8. Barrier heights deduced for TU and TE were the same, with a broad peak of 0. 35 ev for 0. 4 less than x less than 0. 5. Pre-factors for TU and TE were in reasonable agreement with theory for x less than 0. 5 but dropped rapidly for larger x. The effective mass ratio for TU was GAMMA like for x less than 0. 4 and increased to approximately equals 0. 2 for x greater than 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.