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 layers of high resistivity are an important element in GaN-based heterostructure field-effect transistors. A methane ion source was used as the carbon dopant 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 GaN layers with resistivities greater than 106 Ω cm have been grown with high reproducibility and reliability. AlGaN/GaN heterostructures grown on the C-doped semi-insulating GaN-based layers exhibited a high-mobility two-dimensional electron gas at the heterointerface, with room-temperature mobilities typically between 1000 and 1200 cm2/V s, and liquid-nitrogen-temperature mobilities up to 5660 cm2/V s. The carrier density was almost constant, with less than 3% change over the measured temperature range.