A Comparison of N-Polar () GaN Surface Preparations for the Atomic Layer Deposition of Al2O3

Abstract

Nitrogen-polar gallium nitride offers several advantages over Ga-polar GaN for high frequency-high power electronic devices, but its processing has not been fully developed. Here we report on a systematic study of the effect of surface pretreatments on N-polar GaN for metal oxide semiconductor capacitors (MOSCAPs). Bulk n-type GaN () substrates were prepared with a variety of treatments including: HF; HCl; base-piranha; H2 plasma; and no pretreatment for comparison. Then 14nm thick Al2O3 layers were deposited by atomic layer deposition (ALD). Both the original surfaces of GaN and ALD films were characterized by atomic force microscopy (AFM). MOSCAPs were fabricated and characterized by capacitance-voltage (C-V) and current voltage (I-V) measurements. The surface morphology and electrical performance was greatly affected by the pretreatments due to the reactive nature of N-polar GaN. The MOSCAP fabricated on GaN as-received with no additional preparation had the best performance including the smallest hysteresis (0.03V), lowest leakage current density (2.09 × 10−8 A/cm2 at +4V) and total trap density (2.47 × 1010 cm−2eV−1). This was correlated to the smoothest surface morphology (0.23 nm).