III-V Nitride Materials and Electron Devices

The electronic properties of III-V nitride materials make them applicable to high power microwave transistors. They are grown by molecular beam epitaxy or metal organic vapor phase epitaxy, and are direct band gap materials, with alloy gaps ranging from $<$.7V to $>$6.2V. With no native substrates, SiC and sapphire are used. The dislocation properties are acceptor-like for larger band gaps, and donor-like for smaller band gaps. These Wurtzite Crystal materials, grown on the Ga face along the C-axis, have strong spontaneous and piezoelectric polarization. AlGaN/GaN heterojunctions have net polarization sheet charge, inducing an electron sheet charge. Growth without intentional impurity doping, yields $\sim $1X10$^{13}$/cm$^{2}$ electrons in a sheet of 25{\AA} FWHM thickness. Field-effect transistors are fabricated for microwave power amplification.. Their properties include CW normalized power levels $>$10W/mm at 10 GHz. Breakdown electric field strength in the GaN is 3 megavolts/cm, and the sheet current density is 1A/mm. The semiconductor surface is passivated, with silicon nitride, for charge stability. The experimental electron transit velocity of 1X10$^{7}$ cm/s is one third of that originally predicted by Monte Carlo simulations, since the build-up of longitudinal optical phonons was ignored in the simulations. Processing and properties of these transistors will be covered.