TRAP-RELATED EFFECTS IN ALGAAS GAAS HEMTS

Some AlGaAs/GaAs HEMTs display output resistance and transconductance frequency dispersions that are strongly dependent on the applied drain bias V(DS). These frequency and bias dependences have been observed in devices showing a 'kink' effect in the DC current/voltage characteristics. All such phenomena appear to be closely correlated and, because of the presence of deep levels in the AlGaAs layer, may be correlated to DX centres. Electron trapping and detrapping times, which, at low V(DS), are about 3 and 10-mu-s, respectively, can be reduced by almost one order of magnitude by an increase in the drain voltage. Consequently, the related frequency-dependent phenomena disappear at frequencies higher than few megahertz.