Mechanisms of ammonia—MBE growth of GaN on SiC for transport devices

Growth kinetics and electronic properties of unintentionally doped semi-insulating GaN on SiC and high-resistivity GaN on sapphire grown by ammonia molecular-beam epitaxy

“…24 Historically, in the authors' laboratory, a growth regime using a high temperature ͑840-880°C͒ just below the GaN thermal decomposition threshold point and a moderate ammonia flux ͑100 SCCM, BEP= 5 ϫ 10 −5 Torr͒ has been established and applied for GaN high-electron-mobility transistors ͑HEMT͒ devices on sapphire and SiC substrates. 25,26 In this growth regime, the growth is via a three-dimensional ͑3D͒ mode, yielding facetted surface morphology but also large grain size, low defect density, and high electron mobility, mainly due to the higher growth temperature used.…”

“…This trend is similar to what we reported in a previous study about growth regimes on SiC substrates. 24 This phenomenon suggests that oxygen incorporation is inhibited by the 2D surface kinetics, whereas carbon incorporation is insensitive to the surface kinetics. Under the 2D growth regime, the saturated coverage of adsorbed NH x radicals in the adsorption layer likely blocks the adsorption and incorporation of oxygen atoms but cannot block the carbon species.…”

Studies on GaN based HEMT heterostructures on 100-mm silicon grown by molecular beam epitaxy

“…Effect of growth temperature on the properties of GaN was studied and three regions were identified for GaN layer growth [78,89]. Growths performed below 740 °C, called region 1, has resulted in 3D growth mode and poor crystal quality.…”

“…AlGaN/GaN HEMT heterostructures, grown in the growth regime 3 with lower ammonia flow rates exhibit rough surface morphology with lower buffer resistance but good crystal quality [89,93]. However, AlGaN/GaN HEMT heterostructures, grown in the growth regime 2 with high ammonia flow rates resulted in high resistive buffer layers with smoother surface morphologies [82,92].…”

“…insulating GaN buffer using ammonia-MBE was achieved using carbon doping with similar cracked methane source [153,226]. However, their experimental growth conditions involve lower ammonia flows, which resulted in a three dimensional growth mode with rough surface morphology [89]. This signifies that the ammonia-rich growth environment inhibits the incorporation and possibly the activation of carbon in GaN.…”