* Corresponding author. E-mail address: loncierz@polsl.katowice.pl (M. Nowak). Vacuum 57 (2000) 237}242 Application of high-frequency contactless method of PEM investigations to examine near-surface layer of Si and GaAs M. Nowak*, B. Solecka Institute of Physics, Silesian Technical University 40-019 Katowice P.O. Box 221, Poland Abstract The recently reported contactless photoelectromagnetic (PEM) method of determining carrier lifetimes was used to investigate Ga : AS : Te and Si : B samples with polished and grinded surfaces. In the presented experiments the samples were illuminated with radiation of di!erent wavelengths (and di!erent absorption coe$cients) emitted by diode lasers, argon and HeNe lasers acoustooptically modulated up to 100 kHz. The frequency dependence of PEM magnetic #ux registered for cases of excess carriers photogeneration at di!erent depths in a sample are presented and "tted with theoretical dependencies. It allows an evaluation of the bulk and near-surface region electron and hole lifetimes.  2000 Elsevier Science Ltd. All rights reserved. 1. Introduction The carrier lifetime () is one of the most important parameters of semiconductors that determines the usefulness of them for electronics and optoelectronics. Some physical e!ects as well as technological treatment of semiconductors make the  value spatially dependent. The carrier lifetime can have di!erent values in the bulk and in the near-surface region of a sample. Recently, the contactless photoelectromagnetic (PEM) method of determining carrier lifetime was reported [1}4]. Excess carriers (electrons and holes) are photogenerated in a circular region from which they di!use in all directions in the sample, when a semiconductor sample is illuminated by a circular spot of light with photon energy grater than the semiconductor energy gap. The di!using carriers are de#ected due to the Lorentz force and #ow in circles around the illuminated region, when magnetic "eld is applied perpendicularly to the sample surface. The circulating PEM current 0042-207X/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 2 - 2 0 7 X ( 0 0 ) 0 0 1 1 8 - 4