Comparative analysis of structure and interfacial electrical properties of transition metal oxide layers grown on GaN using atomic layer deposition

Comparatively, we present and analyze the structural and electrical parameters of GaN metal-oxide-semiconductor capacitor structures based on a series of the transition metal oxide films, including HfO2, ZrO2, Ta2O5, TiO2, Nb2O5, and Y2O3, along with Al2O3 and SiO2 for reference. We fabricated the GaN metal-oxide-semiconductor capacitor structures using atomic layer deposition, depositing the oxide films onto the GaN substrate at two temperature ranges, 100-125 degrees C and 250-300 degrees C, using either water or ozone as the oxidant. A selective crystallization process was observed in both as-deposited and post-deposition annealed films, with annealing temperatures reaching up to 1200 degrees C, depending on the oxide material and deposition conditions. Enhanced crystallization revealed films composed of either a single phase or two phases, which remained stable without phase transformation under varying deposition or annealing temperature. For the crystallized films, we extracted nanocrystallite sizes (5-30 nm) and strain from grazing incidence X-ray diffraction scans and evaluated the surface roughness from atomic force microscopy images. We analyzed the surface morphology dynamics in relation to the oxide type, oxidant, and deposition and annealing temperatures. From C-V measurements, we extracted the interface trap density and trapped charge density for as- deposited ALD oxide/GaN interfaces, reporting new interface trap density data for Ta2O5/GaN and Y2O3/GaN interfaces. Additionally, we performed GaN band-edge photoluminescence investigations on atomic layer deposition oxide/GaN interface and correlated the results with the morphological and electrical observations. Through this systematic analysis, we demonstrate the competitiveness of the high-k ALD oxides compared to the traditional Al2O3 and SiO2 for GaN metal-oxide-semiconductor capacitor applications.