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The properties of native oxides on different chemically etched GaAs (100) surfaces were investigated by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) analyses. The thickness and composition of native oxides depended not only on the kind but also on the sequence of chemical solutions used, and continuous etching was the most effective method for reducing surface oxide. It was also found that the unetched (just polished) wafer had a Ga-rich surface, the H2SO4 mixture-etched wafer had an As rich surface, and the NaOH mixture-etched and the continuously etched wafer had a nearly stoichiometric surface. All the surfaces of measured wafers were As-oxide rich. To understand the mechanism of chemical etching and the surface state of differently treated wafers, AES data were combined with XPS data. Thus the surface state was estimated and a model for native oxidation process was proposed. These results were explained by the pH-dependent solubility of Ga, As, and their oxides, and the reactivity of As in atmosphere after etching.

The interfacial and electrical properties of atomic layer deposited AlN on n-GaN with different AlN thicknesses were investigated. According to capacitance–voltage (C–V) characteristics, the sample with a 7.4-nm-thick AlN showed the highest interface and oxide trap densities. When the AlN thickness was 0.7 nm, X-ray photoelectron spectroscopy (XPS) spectra showed the dominant peak associated with Al–O bonds, along with no clear AlN peak. The amount of remained oxygen atoms near the GaN surface was found to decrease for the thicker AlN. However, many oxygen atoms were present across the AlN layer, provided the oxygen-related defects, which eventually increased the interface state density. The barrier inhomogeneity with thermionic emission (TE) model was appropriate to explain the forward bias current for the sample with a 7.4-nm-thick AlN, which was not proper for the sample with a 0.7-nm-thick AlN. The reverse leakage currents for both the samples with 0.7- and 7.4-nm-thick AlN were explained better using Fowler–Nordheim (FN) rather than Poole–Frenkel emissions.

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