Theoretical study of improved two-dimensional electron gas density in AlGaN/GaN/AlGaN double heterostructure

Abstract

We evaluate the Alx Ga1–x N/GaN/Aly Ga1–y N double heterostructure (DH) for heterostructure field-effect transistor applications, where the GaN quantum well is compressively strained on a relaxed crack-free Aly Ga1–y N buffer layer, so that the Al content in the Alx Ga1–x N top barrier can be improved as compared with a conventional Alx Ga1–x N/GaN single heterostructure (SH) with the same strain in the Alx Ga1–x N layer. By self-consistently solving the coupled Schrödinger and Poisson equations, we find that the two-dimensional electron gas (2DEG) sheet density in an Al0.6Ga0.4N/GaN/Al0.3Ga0.7N DH is 2.59 × 1013 cm–2, much higher than the 1.71 × 1013 cm–2 in a conventional Al0.3Ga0.7N/GaN SH. The 2DEG sheet density increases with increasing Al content x and decreases slightly with increasing y . With a fixed Al content (x – y ) ratio, y is the key parameter determining the 2DEG density. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)