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 Al 2 O 3 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 SiN x and Al 2 O 3 , high density of positive fixed charges (≈2.382 × 10 13 cm −2 ) is confirmed to be induced at the interface between ALD–Al 2 O 3 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.