High mobility AlGaN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy on semi-insulating GaN templates prepared by hydride vapor phase epitaxy

We report on an extensive study of the growth and transport properties of the two-dimensional electron gas (2DEG) confined at the interface of AlGaN/GaN heterostructures grown by molecular beam epitaxy (MBE) on thick, semi-insulating GaN templates prepared by hydride vapor phase epitaxy (HVPE). Thick (similar to20 mum) GaN templates are characterized by low threading dislocation densities (similar to5x10(8) cm(-2)) and by room temperature resistivities of similar to10(8) Omega cm. We describe sources of parasitic conduction in our structures and how they have been minimized. The growth of low Al containing (xless than or equal to0.05) AlxGa1-xN/GaN heterostructures is investigated. The use of low Al containing heterostructures facilitates the study of the 2DEG transport properties in the previously unexplored regime of carrier density n(s)less than or equal to2x10(12) cm(-2). We detail the impact of MBE growth conditions on low temperature mobility. Using an undoped HVPE template that was residually n type at room temperature and characterized an unusually low dislocation density of similar to2x10(8) cm(-2), we have grown an Al0.05Ga0.95N/GaN heterostructure with a record mobility of 75 000 cm(2)/V s at sheet density of 1.5x10(12) cm(-2) and T=4.2 K. The same heterostructure design grown on a semi-insulating HVPE template yielded a peak mobility of 62 000 cm(2)/V s at a density of n(s)=1.7x10(12) cm(-2) and T=4.2 K. The observation of the fractional quantum Hall effect at filling factor nu=5/3 in the AlGaN/GaN system is reported. It is also demonstrated that thick semi-insulating GaN templates grown by HVPE are a viable substrate for the growth of high electron mobility transistors. Typical Al0.25Ga0.75N/GaN heterostructures exhibit room temperature density of 1.0x10(13) cm(-3) and mobility of similar to1500 cm(2)/V s. The dc and rf characteristics of transistors grown by MBE on a HVPE template are presented. (C) 2002 American Institute of Physics.