Study of semiconductor surfaces and interfaces using electromodulation

The modulation spectroscopy technique of electromodulation (EM) is a major tool for the study and characterization of a number of semiconductor surfaces/interfaces and also for the evaluation of process-induced damage at surfaces. The most useful forms of EM are photoreflectance (PR) and contactless electroreflectance (CER) because they are sensitive to surface/interface electric fields and often yield the sharpest structure (third-derivative lineshape of the unmodulated spectrum in the case of bulk/thin-film material). For sufficiently high electric fields the PR/CER spectra may exhibit Franz-Keldysh oscillations, which are a direct measure of the relevant electric field. Furthermore, PR and CER require no special mounting of the sample and hence can be employed in situ (PR) or non-destructively on wafer-sized material. This article will discuss some recent applications of PR/CER for the investigation of a number of surfaces/interfaces, such as: process-induced effects on the surface of Si; Fermi-level pinning on a number of III-V materials, including low-temperature-grown GaAs (with excess As) and wurtzite GaN; Schottky barrier formation; process-induced damage (sputtering, reactive ion etching, chemical ly assisted ion beam etching) on III-V materials; homojunctions (GaAs/GaAs); heterojunctions (GaAlAs/Ga-As, ZnSe/GaAs, CdTe/GaAs, AlInAs/InP, InGaAs/InP, InGaAs/InAlAs and wurtzite InGaN/GaN); and device structures such as heterojunction bipolar transistors and pseudomorphic high-electron-mobility transistors. A number of these studies have been performed in situ with an ultrahigh vacuum environment. Copyright (C) 2001 John Wiley & Sons, Ltd.