New Gate Dielectric Oxides for GaAs and Other Semiconductors

It is well known that electrons move much faster in GaAs than in Si, and this attribute makes the GaAs-based metal oxide semiconductor field effect transistors (MOSFETs) very attractive for high-frequency, high-speed circuits applications. However, identifying a proper insulating oxide for GaAs has been a problem puzzling researchers over 35 years. Recently we discovered that the use of a mixed oxide dielectric Ga sub 2 O sub 3 (Gd sub 2 O sub 3) sup 1 formed inversion and a accumulation channels on GaAs surfaces, with a low interfacial density of states (D sub (it)) of mid-10 sup (10) cm sup (-2) eV sup (-1). Subsequently, we have demonstrated the p- and n- inversion channel MOSFETs sup 2 and CMOS circuits sup 3. All oxides in this work were prepeared by ultrahigh vacuum deposition form e-beam sources. The initial growth (~1-angstroms) of Ga sub 2 O sub 3 (Gd sub 2 O sub 3) film on GaAs takes place from nucleating a thin epitaxial layer of pure Gd sub 2 O sub 3. In fact, mono-domain, single crystalline Gd sub 2 O sub 3 films (epsilon = 12) can be grown on GaAs (100) surface in the (110) Mn sub 2 O sub 3 structure, and that show leakage currents as low as 10 sup (-4) A/cm sup 2 at 10 MV/cm for a film only 25angstroms thick sup 4. We have extended our studies to other rare earth oxides and other semiconductors. For example, low-D sub (it) GaN MOS diodes and GaN MOSFETs operated at 400C were obtained. The GaN MOSFET has potential applications in high power switching and high temperature device operation. More remarkably, we have found recently that another rare earth oxide, Y sub 2 O sub 3 (epsilon = 18) showed excellent electrical properties as a gate dielectric for Si, to replace the current SiO sub 2, where the thickness is now approaching the quantum limit sup 5.