Investigation of two-dimensional electron gas in AlGaN/GaN heterostructures grown by metalorganic chemical vapor deposition (MOCVD)

Abstract

Temperature dependent Hall effect measurements were carried out on AlGaN/GaN heterostructures grown on sapphire substrates by metalorganic chemical vapor deposition. The samples consist of undoped-AlGaN/GaN single heterostructures (SH) with different Al compositions and intentionally n-doped-Al 0.17Ga 0.83N/GaN SH with different doping levels. The existence of a two-dimensional electron gas (2DEG) was observed for all undoped AlGaN/GaN SH and the mobility was enhanced by increasing the Al composition. In particular, for the AlGaN layer with 13% Al fraction the mobility saturated at 5000 cm 2/V s below 80 K. However, when AlGaN layer is doped, the situation was changed. In the case of lightly doped AlGaN layer, the 2DEG could not be observed. When the doping level in AlGaN is increased, the 2DEG was demonstrated again together with an enhancement in the electron mobility. These behaviors are attributed to the strain-induced piezoelectric effect and silicon doping induced-screening effect. This result should be highly emphasized in designing GaN-based electrical devices.