Short Pulse Transfer Characteristics of Al sub x GA sub (1- x) As/GaAs and Al sub x Ga sub (1-x) As/In sub y Ga sub (1- y) As Modulation Doped Heterojunction FETs.

Short pulse drain current versus gate voltage transfer characteristics have been measured for modulation doped HFETs with the following donor-layer/channel-layer combinations: (i) Al sub (0.3) Ga sub (0.7) As/GaAs, (ii) Al sub (0.2) Ga sub (0.8) As/GaAs, (iii) Al sub (0.3) Ga sub (0.7) As/In sub (0.2) Ga sub (0.8) As, and (iv) Al sub (0.2) Ga sub (0.8) As/In sub (0.2) Ga sub (0.8) As, and have been compared with the d.c. transfer characteristics. These measurements are relevant for high speed switching in HFET circuits. Significant threshold shifts exist between the d.c. and short pulse characteristics for the structures with an n sup + -Al sub s(0.3) Ga sub (0.7) As donor layer, while the corresponding shifts for structures with an n sup + -Al sub (0.2) Ga sub (0.8) As donor layer are relatively small, or virtually non-existent.