Electron velocity saturation in heterostructure field-effect transistors

Results on gate-length scaling of the performance of enhancement-mode heterostructure field-effect transistors (HFETs) for gate lengths of between 0.4 and 10 mu m are reported. The devices studied were fabricated by a self-aligned gate process. Transconductances as large as 534 mS/mm were achieved with 0.4- mu m devices. Two types of pseudomorphic AlGaAs/InGaAs/GaAs heterostructure are compared. One of them is used for modulation-doped FETs and the other for doped-channel FETs. It is found that the effects of electron velocity saturation are different for the two types of device due to the dominance of charge transfer and gate leakage in the conventional modulation-doped device. The experimental results are explained in the framework of a simple charge control model. >