Stability of performance and interfacial problems in GaAs MESFET's

Interface effects in GaAs MESFET's were investigated from the viewpoint of stability of performance. It was clarified, on the basis of a simple analytical model, that even a small fluctuation of the effective channel thickness due to interface effects causes drastic changes or drifts in performance characteristics of a GaAs MESFET. Paying attention mainly to the behavior of drain current, the interface effects were experimentally investigated for VPE-gown 1-µm-gate GaAs MESFET's with and without a buffer layer. It was revealed that they are due to deep acceptors or hole traps, which exist at the interfaces and in the buffer layer and the semi-insulating substrate, and found that the long-term drift is attributed to Cr in the buffer layer as well as in the semi-insulating substrate.