Composition and growth of thin anodic oxides formed on InP (100) T. Djenizian a , G.I. Sproule b , S. Moisa b , D. Landheer b , X. Wu b , L. Santinacci a , P. Schmuki a, *, M.J. Graham b a Department of Material Science, LKO, University of Erlangen-Nuremberg, Martensstr. 7, D-91058 Erlangen, Germany b Institute for Microstructural Sciences, National Research Council of Canada, Ottawa, Canada K1A 0R6 Received 22 November 2001; received in revised form 5 March 2002 Abstract Thin anodic oxides ( B/100 A ˚ ) were formed on p-InP (100) in phosphate solution (0.3 M NH 4 H 2 PO 4 ) and in sodium tungstate solution (0.1 M Na 2 WO 4 × /2H 2 O) at different temperatures (25 and 80 8C) and potentials (1  /8 V). Thickness and composition were determined by different surface-analytical techniques including Auger electron spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and transmission electron microscopy. In general, it has been observed that double-layered films are obtained with an outer In-rich layer. The thickness of the outer layer, oxide morphology and roughness as well as the composition of the duplex structure are strongly dependent on the temperature and the composition of the electrolyte. It has been found that oxides formed in phosphate exhibit a higher stability against dissolution compared with oxides formed in tungstate. The latter contain a large amount of In 2 O 3 , which leads to poor electrical properties. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Anodic oxide; InP; Surface analysis; Double-layered films; Electrical properties 1. Introduction Due to their direct band gap III /V, semiconductor compounds such as GaAs and InP have been the subject of a large number of investigations to fabricate a variety of devices used for optical communication and high- speed electronic systems. In order to develop these technologies, oxidation of III  /V compounds, in parti- cular GaAs, has been extensively studied [1 /3] with emphasis on surface-analytical techniques [4  /6]. Inves- tigations have also focused on InP, an attractive candidate for a wide range of applications. Various devices using InP have been fabricated including metal  / insulator  /semiconductor field effect transistors (MIS- FETs), photo-electrochemical solar cells [7], light emit- ting diodes [8] and components for optical fiber communications [9]. But in contrast to Si, the thermal oxide formed on InP is of low quality and tends to be too conductive for use as a gate insulator. In comparison with thermal oxidation, anodic oxida- tion results in a significant improvement in electrical properties. Anodic layers can be grown on InP using both aqueous (0.1 N KOH) [10] and non-aqueous (0.1 N sodium salicylate in ethanol) electrolytes [11]. Results reported have shown improved oxides in terms of resistivity, but in all cases high leakage currents have been observed limiting the field of application. Investi- gations dealing with anodic oxides formed in electrolytes such as AGW (a mixed solution of glycol and water) and sodium tungstate (0.1 M Na 2 WO 4 × /2H 2 O) have also been reported [12  /17]. In the present work, the composition and growth of anodic oxide films are studied in sodium tungstate and phosphate solutions at different temperatures. The influence of the potential and temperature on the chemical composition and thickness of the oxides was studied by Auger electron spectroscopy (AES) and X- ray photoelectron spectroscopy (XPS) complemented by transmission electron microscopy (TEM). The oxide morphology has been assessed by scanning electron microscopy (SEM) and atomic force microscopy * Corresponding author. Fax:  /49-91318527582. E-mail address: schmuki@ww.uni-erlangen.de (P. Schmuki). Electrochimica Acta 47 (2002) 2733  /2740 www.elsevier.com/locate/electacta 0013-4686/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII:S0013-4686(02)00138-X