XPS study of Au/GaN and Pt/GaN contacts
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Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 23
XPS study of Au/GaN and Pt/GaN contacts R. Sporken, C. Silien, F. Malengreau, K. Grigorov, R. Caudano Facultés Universitaires Notre-Dame de la Paix , Belgium F. J. Sánchez, E. Calleja, E. Muñoz Dpt. Ingeniería Electrónica, E.T.S.I. Telecomunicación, Politécnica, Ciudad Universitaria B. Beaumont, Pierre Gibart Centre de Recherche sur l'Hetero-Epitaxie et ses Applications, CRHEA-CNRS This article was received on June 10, 1997 and accepted on September 4, 1997.
Abstract Au/GaN and Pt/GaN contacts have been studied with XPS. According to XPS depth profiling, the N signal is weak in the region below the metal contact and the Pt or Au signal decreases much more slowly than expected for a sharp interface. Next, we have performed in situ studies of the formation of Au contacts on GaN. In contrast to the results from depth profiling, we observe 2D growth and little or no chemical interaction between Au and GaN. This suggests that conventional calculations of sputtering yields and ion-beam-induced mixing cannot be applied to the analysis of noble metal/GaN depth profiles. Heating during or after Au deposition results in strong clustering, observed by both XPS and AFM. The Schottky barrier height measured by XPS is 1.15 eV.
1. Introduction GaN has attracted considerable interest in recent years because of its wide range of applications, including blue/ultra-violet light emitting devices, ultra-violet detectors and high power/high temperature electronics. These applications are possible because of the large direct band gap of GaN (3.4 eV), and because of its remarkable stability in aggressive environments. In this context, it is important to study the properties of metal-GaN contacts, because one must be able to produce stable metal contacts with well-defined electrical properties. In this work, Schottky contacts of Pt and Au on GaN were studied by XPS. In the first part of this paper, we describe the study of such contacts by depth profiling with x-ray photoelectron spectroscopy (XPS). This technique is destructive and can introduce several artefacts due to the use of an energetic ion beam to sputter through the metal layer. Therefore, in the second part of the paper, a detailed in situ study by XPS of the formation of Au/GaN interfaces is described. Finally, we have investigated the effect of thermal annealing on the structure of the Au/GaN interface, and have found that Au has a strong tendency to form large clusters on GaN at elevated temperature.
2. Experimental The GaN samples are epitaxial films of GaN grown on (0001) sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) at atmospheric pressure. All samples are n-type, with carrier concentration in the 1017 - 1018 cm-3 range. Details about the growth of such layers are published elsewhere [1]. For the study of metal-GaN by XPS depth profiles, the samples were transferred into a metallization chamber where a 150 nm thick layer of Pt or Au was deposited using an electron gun evaporat
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