GAAS-BASED METAL-INSULATOR-SEMICONDUCTOR STRUCTURES WITH LOW INTERFACE TRAPS USING MOLECULAR-BEAM EPITAXY AND CHEMICAL-VAPOR-DEPOSITION

The performance of GaAs-based field-effect transistors (FETs) in switc hing and power applications can be enhanced substantially by employing a metal-insulator-semiconductor (MIS) structure. Attempts thus far ha ve fallen short due to large interface trap concentrations, frequency dispersion, and hysteresis. By taking advantage of an in-situ process approach, we successfully gated insulator - GaAs structures with excel lent interfacial properties. The structures utilize a Si interface lay er or a composite Si/Ge layer grown on GaAs followed by a Si3N4 dielec tric layer, all using a III-V molecular beam epitaxy (MBE) system conn ected by an ultrahigh vacuum transfer tube to an adjacent electron cyc lotron resonance (ECR) plasma enhanced chemical vapor deposition (CVD) system. This pseudo-in-situ feature in concert with recently implemen ted vacuum connected scanning tunneling microscopy (STM) and X-ray pho toelectron spectroscopy (XPS) allows investigations of the essential i nterface layers. High/low frequency capacitance-voltage, conductance v ersus frequency, and metal-insulator-semiconductor field-effect transi stors (MISFETs) were used for a comprehensive characterization of the n-type MIS structures. From the stringent conductance measurements, in terface state densities in the high 10(10) eV(-1) cm(-2) have been obt ained. The hysteresis is about 150 mV for a field swing of +4 to -4 MV /cm. The frequency dispersion is nearly zero except near inversion whe re its value is about 100 mV. Self aligned gate depletion mode MISFETs having 3 mu(m) gate lengths exhibited transconductances of 169 mS/mm for the pseudomorphic InGaAs channels and about 100-140 mS/mm for GaAs channels.