Abstract: A high electron mobility transistor photodetector includes an undoped GaAs buffer, a p-type GaAs layer positioned above the undoped GaAs buffer that is between 0.5 to 1 &mgr;m in thickness, an undoped low temperature GaAs layer positioned above the p-type GaAs layer, an undoped GaAs layer positioned above the low temperature GaAs layer, a layer of undoped InGaAs positioned above the undoped GaAs layer, a layer of undoped AlGaAs positioned above the layer of InGaAs, an n+ AlGaAs charge-suppling layer positioned above the layer of undoped AlGaAs, an n+ GaAs contact layer positioned above the n+ AlGaAs charge-supplying layer, and source and drain ohmic contacts positioned above the n+ GaAs contact layer. A negative bias voltage is applied to the p-type GaAs layer to sweep the holes from the photo-absorptive layer which greatly increases the speed and responsiveness of the device.

Abstract: A reduced 1/f low frequency noise high electron mobility transistor is obned based on the realization that in modulation-doped heterostructure transistors the inherent bandbending in the high bandgap material spacer layer allows certain trap energy levels to cross or approach the Fermi level at or near the 2DEG interface. For the case of AlGaAs/GaAs HEMTs or AlGaAs/InGaAs/GaAs pseudomorphic HEMTs the composition of the spacer layer is graded to provide for the conduction band energy to have a negative slope near the spacer layer/2DEG interface. This bandbending pulls interface trap energy levels away from the Fermi level and significantly reduces f.sub.t (1-f.sub.t) and the spectral density of the 1/f low frequency noise.