Controlling two-dimensional electron gas density through surface states in ultra-thin-barrier AlGaN/GaN heterostructures

A method to control the two-dimensional electron gas (2DEG) density in AlGaN/GaN heterostructures through post-epitaxial device processing is investigated. This control was achieved by dielectric film deposition and subsequent annealing on an ultra-thin 5-nm Al0.22Ga0.78N barrier layer. The 2DEG density, estimated from sheet resistance assuming constant mobility, was found to be tunable from 8.3 × 107 cm−2 before dielectric film deposition to 4.5 × 1012 cm−2 after SiO2 film deposition and annealing. Hard x-ray photoelectron spectroscopy analysis confirmed a maximum shift of 0.8 eV in the surface pinning level, attributed to the dielectric film deposition and annealing. Numerical calculations indicate that for an AlGaN barrier layer thickness of approximately 5 nm, a surface pinning energy change of ∼0.8 eV can induce a 2DEG density variation of 6–8 orders of magnitude, supporting the validity of the experimental results.