The influence of composition and unintentional doping on the two-dimensional electron gas density in AlGaN/GaN heterostructures

Abstract

We have studied the influence of Al content, AlGaN layer thickness, and unintentional background doping by oxygen on the two-dimensional electron gas (2DEG) density in AlGaN/GaN heterostructures. Hall measurements were made on samples grown with molecular beam epitaxy. The 2DEG densities in the range 2–3×1013 cm−2 were measured. A one-dimensional Schrodinger-Poisson model was used to describe the heterostructure. The calculations gave two-dimensional electron densities in accordance with measured values. The electron density is very sensitive to the Al concentration in the AlGaN layer, whereas the sensitivity to layer thickness is small. Our simulations also showed that the two-dimensional concentration increased 50% when the free-carrier concentration changed from 1015 cm−3 to 1018 cm−3. The relation between donor concentration and free-carrier concentration was found to agree when using oxygen ionization energy as a parameter.