Aluminum oxide as passivation and gate insulator in GaAs-based field-effect transistors prepared in situ by metal-organic vapor deposition

Application of GaAs-based metal-oxide-semiconductor (MOS) structures, as a "high carrier mobility" alternative to conventional Si MOS transistors, is still hindered due to difficulties in their preparation with low surface/interface defect states. Here, aluminum oxide as a passivation and gate insulator was formed by room temperature oxidation of a thin Al layer prepared in situ by metal-organic chemical vapor deposition. The GaAs-based MOS structures yielded two-times higher sheet charge density and saturation drain current, i.e., up to 4×10 12 cm −2 and 480 mA/mm, respectively, than the counterparts without an oxide surface layer. The highest electron mobility in transistor channel was found to be 6050 cm 2 /V s. Capacitance measurements, performed in the range from 1kHz to 1MHz, showed their negligible frequency dispersion. All these results indicate an efficient suppression of the defect states by in situ preparation of the semiconductor structure and aluminum oxide used as a passivation and gate insulator.