Surface contact doping effect of Si on AlGaN/GaN heterojunction

A thin layer of Si was deposited on a series of AlGaN/GaN heterojunctions with sub-critical barrier thicknesses, resulting in the formation of a two-dimensional electron gas (2DEG) at the heterointerface, where no 2DEG was present initially. After the first Si deposition, the sheet resistance is reduced by over five orders of magnitude to 490–640 Ω/□, with 2DEG densities of 5.0–8.2 × 1012 cm−2 and mobilities exceeding 1550 cm2/V s. Moreover, we find that the 2DEG disappears after the removal of the surface Si layer, which can be explained by a contact doping effect induced by Si at the AlxGa1–xN surface. The surface contact doping effect of Si leads to a reduction in surface potential, as revealed by x-ray photoelectron spectroscopy. Further electrostatic analysis estimates that the Si-induced energy levels are located below the conduction band edge of AlxGa1–xN by 0.36 eV for GaN, 0.50 eV for Al0.1Ga0.9N, and 0.63 eV for Al0.18Ga0.82N.