High-indium modulation doped field effect transistors on GaAs substrates

We have grown InxGa1−xAs modulation doped field effect transistors (MODFETs) using novel buffer layer schemes on GaAs substrates with x values up to 0.5. The MODFET active layers were grown at substrate temperatures between 500 and 520 °C and characterized by x-ray diffraction, photoluminescence, and Hall effect measurements. MODFET devices with 0.15 μm gate length were fabricated, and dc and rf tested. Our work has indicated that the electron mobility in the MODFETs is a function of the growth mode, i.e., two-dimensional (2D) layer-by-layer versus three-dimensional island growth. MODFET performance, the ability to maintain a streaky reflection high-energy electron diffraction pattern, as well as morphology had a very strong correlation. With these observations in mind we used a buffer layer scheme to give 2D growth fronts for InxGa1−xAs with x values up to 0.5, which is a modification of the buffer scheme described in K. Maezawa and T. Mizutani, IEEE Trans. Electron Devices 37, 1416 (1990). For In0.34Ga0.66As channel MODFETs we observed a room-temperature electron mobility of 6620 cm2/V s with a 2D carrier density of 5.9 × 1012 cm−2 (double-doped channel), a dc transconductance of 800 mS/mm and a rf gain of 13.5 dB at 35 GHz for a 0.15 μm gate length.