Investigation of Native Oxide Layers on Untreated and Chemically Treated InAlN Surfaces by X-ray Photoelectron Spectroscopy

Abstract

ThecharacteristicsofnativeoxidelayersonuntreatedandchemicallytreatedInAlNsurfaceswereinvestigatedbyX-rayphotoelectron spectroscopy (XPS). Ammonia (NH4OH), hydrochloric acid (HCl), and hydrofluoric acid (HF) were used for chemical treatment. The native oxide layer on an untreated InAlN surface was found to mainly consist of hydroxide components. These hydroxides were completely removed by HF treatment, whereas the other treatments resulted in incomplete removal. NH4OH treatment increased the intensity of the In-related hydroxide component, indicating that oxidation had occurred. This was confirmed by successive NH4OH/HF treatments applied to an ultrathin InAlN layer, which resulted in etching. © 2012 The Electrochemical Society. (DOI: 10.1149/2.004201ssl) All rights reserved. improve the device performance, an appropriate fabrication process should be applied to control the metal-semiconductor and insulator- semiconductor interfaces based on an understanding of the surface native oxide layer. However, the chemical composition of the native oxide layer has not been investigated in detail for InAlN. Therefore, the characteristics of the native oxide layer should be investigated to find a removal method, particularly one using ordinary acids familiar to the production lines used to fabricate semiconductor devices, as an appropriate pretreatment prior to interface formation. In addition, the analysis of surface native oxide layers may lead to knowledge useful for the device fabrication process. Previously, the hydrofluoric acid (HF) treatment was found to be useful for eliminating the effect of surface native oxide layers on measuring band offset at the InAlN- GaN hetero structures by XPS. 5,6 However, the detailed analysis of chemical bonding in native oxide layers have not been achieved. In addition, any other ordinary less dangerous chemicals to remove the InAlN native oxide layers were not investigated or compared. Here we investigate the composition of the native oxide layer and compare the efficiency of oxide removal among treatments using ammonia (NH4OH), hydrochloric acid (HCl), and HF solutions. We analyze the native oxide components before and after the chemical treatments by X-ray photoelectron spectroscopy (XPS). In0.17Al0.83N layers were grown on GaN buffer layers on sapphire (0001) substrates by metal-organic vapor phase epitaxy (MOVPE). The In molar fraction 0.17 of the InAlN layer was confirmed by X-raydiffraction(XRD)foralloverthe3-inchwafertobedividedinto pieces for the present XPS measurements. Consequently, the molar fraction was uniform for all samples under investigation. The initial surface before each treatment referred to as the untreated surface, was the air-exposed surface of InAlN after taking out the sample from the growth chamber. The HF and HCl treatments were carried out at room temperature, whereas the NH4OH treatment was carried out at 50 ◦ C. Each chemical treatment was followed by rinsing with deionized (DI) water (18 Mcm - quality), and blowing with pure nitrogen, then the samples were immediately introduced into vacuum. DI water rinsing was necessary to prevent pollution of the vacuum system by residual chemicals. XPS was performed using a monochromated Al-Kα X-ray source (1486.6 eV). The binding energy shift induced by the charging oftheinsulatingsubstratewascalibratedbyadjustingthepeakposition oftheC1scorelevelto285.0eVforeachsamplesurface.Ifnecessary, the photoelectron exit angle, θ, (defined as the elevation angle respect to the sample surface) was changed by tilting the sample to vary the