Indium Phosphide Surface Modifications By Electrochemistry and Ionic Sputtering

Abstract

The electrochemistry of III-V semiconductors such as Indium Phosphide (InP) has been studied in great detail, in particular for its reproducible electrochemical signatures, both in the dark and under illumination where photocurrents appear. However, little is known about the electrochemical behavior of such materials when it has been modified by a physical treatment as ionic bombardment. Such treatments are currently knowing an increasing interest for many studies where chemical depth-profile analysis is wanted. The electrochemistry of InP before and after sputtering with different parameters (energy, projectile size...) will be presented. The study of i-V curves, Open Circuit Potential, Mott Shottky plots and Nyquist plots of samples obtained with different conditions would indicate the relationship between such modification and changes in band bendings, interface states, etc. The coupling of electrochemical studies with XPS analyses during bombardments is an original tool which would become in the future a key approach for several systems, especially heterostructures. The evolution of the electrochemical behavior induced by perturbation can be exploited as very accurate surface probing. Another really promising interest of such experiments is the ability to recover with electrochemical or chemical treatments the initial properties of the damaged semiconductor surfaces. The purpose of this work is to study in detail the effects of different bombardments on InP, from monoatomic projectiles known to strongly modify crystallinity of surfaces to argon clusters, promising for characterization of sensitive materials thanks to a low energy by atom in the cluster (no ion implantation). While XPS profiling of crystalline materials by ionic bombardment is performed, a core level peak broadening is generally observed. In the case of binary semiconductors, changes in the atomic ratios may also appear. These effects can be interpreted as the appearance of disorder in a crystalline structure and a preferential etching. The objective here is the correlation between XPS and interfacial electrochemistry. Such approach allows to know the overall changes in the properties of the electrode induced by various treatments and therefore highlights the limits of interpretations in XPS profiling study (under vacuum) and the possible reorganizations when delivered to the air. Modifications of the electrode could be followed by its electrochemical modification toward hydrogen evolution leading to different cathodic decomposition of the material. After monoatomic sputtering, indium enrichment and electrochemical modification are observed and related to the level of perturbation. The photocurrent is no longer detectable, showing formation of a film that modifies the semiconductor response. The Mott-Schottky plot strongly flattens over the entire potential gap of InP. Nyquist plots also show an increase in the charge transfer resistance at the open circuit potential. Using cluster of thousands of argon atoms allows better control of the induced modifications. A regime where the characteristics of the semiconductor can be retrieved by anodic dissolution or chemical etching will be particularly investigated.