Growth, formation, and stability of anodic oxides obtained on n-InP were investigated by coupling electrochemical methods and X-ray photoelectron spectroscopy ͑XPS͒ analyses. Photocurrent transients and capacitance measurements performed before and after the semiconductor surface oxidation exhibit new electrical interfacial properties, whereas XPS analysis gives access to chemical composition and estimation of oxide layer thickness. In this work, using a galvanostatic method, oxidation of the InP surface has been studied at pH 9 for two current densities: 0.2 and 12 mA cm −2 . Using transient photocurrent and Mott-Schottky behavior as in situ probes, we have pointed out several steps for the InP oxidation process, correlated to a gradual oxide coverage which is evidenced by XPS characterization. The current density chosen to perform the oxidation governs the resulting chemical composition, texture, and electrical properties of the oxide. For low current density, the anodic mechanism varies progressively from a pure semiconductor oxidation process to a solvent oxidation contribution. For high current density, this trend disappears whereas semiconductor oxidation continues to take place.

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The photo oxidation of n-InP is followed by photocurrent transient measurements in a polaron cell at pH 9. For each photo-anodic treatment, the correlation between P oxidised /P InP , determined by XPS analyses and photocurrent transient analyses is investigated. The results suggest that all coulometric charge used for the oxidation mechanism is entirely included in the "oxide" film present onto InP. The control of the thickness and the coverage of the "oxide" film are followed with high precision. We evidence a very thin "oxide" film with an important surface coverage. This result explains the electrically blocked properties of this "oxide" film. Consequently, photocurrent transient is an accurate technique to investigate, in situ, the "oxide" growth on n-InP. IntroductionThe control of thin "oxide" film on semiconductors plays an important role in semiconductor technologies. Unstable devices based on III-V compounds are often due to a poorly controlled "oxide" film. Wet and dry chemical and electrochemical methods have been explored to reach optimised interfaces with time stabilised electrical properties. The complexity and the diversity of "oxide" growth onto III-V compounds have been intensively studied and stay today an actual challenge to increase the performance of high speed and optoelectronic devices [1][2][3][4]. The aim of this paper is to shown how the electrochemical approach coupled with surface analyses (X-ray photoelectron spectroscopy (XPS) and photoluminescence experiments) provides a qualitative and quantitative characterization of an "oxide" growth and its properties. The anodic oxidation was performed in a potentiostatic mode under illumination. Photocurrent transient, recorded under anodic polarisation, coupled with surface analyses (XPS), give information on the thickness, on the chemical composition, on the stability, and also on the passivation properties of "oxide" films [5][6][7]. In this paper, we applied this approach on n-InP semiconductor at pH 9. In this experimental condition, using controlled illumination time and constant polarisation mode, the photocurrent transient exploration is used to characterize the photo anodic "oxide". Indeed, we observed a thin "oxide" film onto n-InP of which thickness is controlled to obtain a precision of one monolayer equivalent.

Anodic oxides grown on n-InP under applied potential and illumination exhibit important blocking properties against hole transfer from the valence band. In this work we focus our attention on the blocking properties of these anodic oxides against electron transfer from the conduction band. Therefore, electron transfer which occurs during the characteristic cathodic reaction, i.e., hydrogen formation associated with semiconductor decomposition, has been studied for photo-oxidized surfaces. The cathodic behavior of n-InP previously photo-oxidized is compared to the behavior of a nonoxidized semiconductor surface. Our purpose is to study both the anodic oxide blocking properties and how the cathodic decomposition of anodic oxide-covered surfaces is modified. This work points out a complex cathodic behavior for electrodes covered with oxides. Two stages are distinguished. During the first stage of cathodic process, anodic oxide decomposition is the only reaction which takes place at the semiconductor interface. This reaction occurs with an overpotential evidencing the presence of an energetic barrier in anodic oxide. Then, when the anodic oxide is completely decomposed, a second stage occurs corresponding both to the cathodic decomposition of the semiconductor and to H2 evolution. © 2004 The Electrochemical Society. All rights reserved.