Semi-insulating C-doped GaN and high-mobility AlGaN/GaN heterostructures grown by ammonia molecular beam epitaxy

A method of growing semi-insulating GaN epilayers by ammonia molecular beam epitaxy through intentional doping with carbon is reported. Thick GaN laye rs of high resistivity are an important element in GaN-based heterostructur e field-effect transistors. A methane ion source was used as the carbon dop ant source. The cracking of the methane gas by the ion source was found to be the key to the effective incorporation of carbon. High-quality C-doped G aN layers with resistivities greater than 10(6) Omega cm have been grown wi th high reproducibility and reliability. AlGaN/GaN heterostructures grown o n the C-doped semi-insulating GaN-based layers exhibited a high-mobility tw o-dimensional electron gas at the heterointerface, with room-temperature mo bilities typically between 1000 and 1200 cm(2)/V s, and liquid-nitrogen-tem perature mobilities up to 5660 cm(2)/V s. The carrier density was almost co nstant, with less than 3% change over the measured temperature range. (C) 1 999 American Institute of Physics. [S0003-6951(99)00933-X].