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 (∼20μm) GaN templates are characterized by low threading dislocation densities (∼5×10 8cm -2) and by room temperature resistivities of ∼10 8cm. We describe sources of parasitic conduction in our structures and how they have been minimized. The growth of low Al containing (x≤0.05) Al xGa 1-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≤2×10 12cm -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 ∼2×10 8cm -2, we have grown an Al 0.05Ga 0.95N/GaN heterostructure with a record mobility of 75000cm 2/Vs at sheet density of 1.5×10 12cm -2 and T=4.2K. The same heterostructure design grown on a semi-insulating HVPE template yielded a peak mobility of 62000cm 2/Vs at a density of n s=1.7×10 12cm -2 and T=4.2K. The observation of the fractional quantum Hall effect at filling factor ν=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 Al 0.25Ga 0.75N/GaN heterostructures exhibit room temperature density of 1.0×10 13cm -3 and mobility of ∼1500cm 2/Vs. The dc and rf characteristics of transistors grown by MBE on a HVPE template are presented.
ASJC Scopus subject areas
- Physics and Astronomy(all)