| This thesis reports on the application of molecular-beam epitaxy (MBE) to AlGaAs/InGaAs single quantum-well modulation-doped field-effect transistors (MODFETs). This type of MODFET requires a high-quality high-barrier AlGaAs buffer, a high electron velocity InGaAs quantum-well channel and an optimized AlGaAs electron supplying layer which can supply a large density of high velocity electrons. The mechanisms for unintentional defect and impurity incorporation during molecular-beam epitaxial growth of each of these three regions must be fully understood in order to achieve complete structures with enhanced device performance. This thesis describes an experimental investigation of these mechanisms.;Atomic planar-doped electron supplying layers and lattice-mismatched InGaAs quantum-well channels were then investigated. Atomic planar doping is shown to allow higher 2DEG sheet densities than conventional uniform doping. The influence of InGaAs quantum well width, growth temperature, and arsenic flux on defect and impurity incorporation, and on transistor performance has been characterized. It is shown that, with the appropriate choice of these parameters, high-performance In;The techniques reported in this thesis have allowed the first microwave MODFET with over 1 A/mm current density to be achieved. In addition, a 0.2;The influence of the AlGaAs buffer on two-dimensional electron gas (2DEG) transport has been characterized. Improvements in 2DEG transport have been obtained by replacing the AlGaAs buffer with an optimized AlGaAs/GaAs superlattice buffer and by using substrates which are intentionally tilted off (001). It is shown that the substrate tilt angle (0 to 10... |
