The Modulation Effect of LPCVD-Si x N y Stoichiometry on 2-DEG Characteristic of UTB AlGaN/GaN Heterostructure

In this work, the impact of low-pressure chemical vapor deposition (LPCVD)-Si _x N _y stoichiometry on 2-D electron gas (2-DEG) transport characteristics of the AlGaN (3.9 nm)/GaN heterostructure and the underlying mechanism of increased 2-DEG density are studied, which reveals a new perspective of improving AlGaN/GaN performance by dielectric engineering. Among the AlGaN/GaN passivated by the LPCVD-Si _x N _y with tailored stoichiometry, the 2-DEG density and mobility in the Si-rich sample were significantly improved by 25% and 16.3% compared with the N-rich sample, respectively. Accordingly, 30% reduction in sheet resistance of AlGaN/GaN heterostructure is obtained. The potentially strained-induced enhancement of piezoelectric polarization and corresponding 2-DEG variation by the Si _x N _y passivation layer was excluded by the negligible change in Raman spectra among the different samples. Alternatively, the X-ray photoelectron spectroscopy (XPS) showed that the varied stoichiometry of the Si _x N _y enables a discernible modulation effect of heterostructure energy-band. The reduced surface potential in the sample passivated by Si-rich Si _x N _y attributes to the pronounced Ga dangling bonds (DBs) at the LPCVD-Si _x N _y /AlGaN interfaces, which provides the near-conduction band (NCB) states and leads to enhanced 2-DEG accumulation.