Presence of High Density Positive Fixed Charges at ALD–Al2O3/GaN (cap) Interface for Efficient Recovery of 2‐DEG in Ultrathin‐Barrier AlGaN/GaN Heterostructure

The ultrathin‐barrier (UTB) AlGaN/GaN heterostructure exhibits great promise as a technology for manufacturing high‐performance normally OFF GaN metal–insulator–semiconductor high‐electron‐mobility transistors (MIS–HEMTs) due to its unique gate recess‐free feature. However, a critical challenge in UTB MIS–HEMTs is the recovery of the 2D electron gas in the access region, particularly with regard to achieving low ON resistance. In this study, a new approach is proposed to address this issue by utilizing a low‐thermal‐budget Al2O3 film grown through atomic layer deposition (ALD). By analyzing the capacitance–voltage characteristic and correlating it with the threshold voltage shift versus dielectric thicknesses for SiNx and Al2O3, high density of positive fixed charges (≈2.382 × 1013 cm−2) is confirmed to be induced at the interface between ALD–Al2O3 and GaN (cap), which is also in good agreement with 1D Poisson simulations of energy band diagrams. The positive charges are probably originated from the interface AlAl bonds revealed by X‐Ray photoelectron spectroscopy analysis.