1063-7826/05/3906- $26.00 © 2005 Pleiades Publishing, Inc. 0629 Semiconductors, Vol. 39, No. 6, 2005, pp. 629–635. Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 39, No. 6, 2005, pp. 660–666. Original Russian Text Copyright © 2005 by Odrinskiœ. 1. INTRODUCTION Currently, in order to study deep levels in high-resis- tivity semiconductors, researchers make efficient use of photoinduced-current deep-level transient spectros- copy (PICDLTS [3] or PICTS), which was first sug- gested in [1,2]. This method is based on an analysis of the temperature dependence of the photocurrent relax- ation kinetics. It makes it possible to obtain the same information as with the method of thermally stimulated conductivity (TSC) (the energy positions of deep levels E t and the capture cross section of nonequilibrium carri- ers S nt ) from a single temperature scan, but it has a higher sensitivity [4] and accuracy when determining the parameters of deep levels [5]. However, opinions differ as to whether this method can be used to estimate the concentration of deep levels, which casts doubt on its role as a valuable method for studying this phenomenon. For example, in [6–9], the PICTS method was used to estimate the concentration of deep levels, and estimates [10] made using this method and the method ofoptical absorption have been found to coincide with an accuracy of 25%. At the same time, the concentration of deep levels is often deter- mined using less effective procedures. For example, in [11], the PICTS method was used to estimate the rel- ative concentration of deep levels, and the estimate was calibrated by measuring the space-charge limited cur- rent. It was noted in [11–15] that it is difficult to esti- mate many parameters of the base model in practice and that the method cannot be used to estimate the con- centration of deep levels. This opinion is often related to the disagreement between the parameters of deep- level signals (peak heights) in a set of PICTS spectra 1 and the phenomenological model [5]. In this study, we 1 The derivation of the peak-height ratio for the set of spectra is given in the Appendix. demonstrate the possibility of making such an estimate using the example of a series of semi-insulating CdS single crystals. 2. EXPERIMENTAL RESULTS Using the PICTS method, we studied several semi- insulating CdS crystals (with a resistivity of 10 8 – 10 12 Ω cm) grown using the same method as described in [16] and possessing a varying stoichiometric compo- sition. Except for the ratio of the partial vapor pressures of Cd and S p S / p Cd at the solidification front, the crys- tals were grown with constant growth parameters [17]. In [18], results from studying the effects of excitation using light with a photon energy hν = 2.55 eV were reported. Based on the requirement for a more uniform excitation of the sample bulk and a decrease the effect of the surface, the PICTS measurements were carried out using excitation by quasi-monochromatic light with hν < E g (hν = 2.3–2.5 eV), where E g is the band gap. The radiation of a DKSSh500 xenon lamp, which was passed through an MSD1 monochromator, was used. The width of the entrance and exit slits was 5 mm, which corresponds to a spectral range of ~300 Å. A par- tial set of results for excitation with hν ≤ E g was pre- sented in [4]. It was concluded that the mechanism of trap filling due to the thermal capture of nonequilibrium carriers from the band (thermal mechanism), consid- ered in the PICTS model, is insufficient to explain the detection of a dominant deep level in the spectra, and an optical mechanism of filling due to direct optical tran- sitions between the level and the bands was proposed. Under excitation at hν = 2.35 eV, several deep levels were found (see the spectra in Fig. 1) that were not detected under excitation with hν = 2.55 eV, and some ELECTRONIC AND OPTICAL PROPERTIES OF SEMICONDUCTORS Determination of the Concentration of Deep Levels in Semi-insulating CdS Single Crystals by Photoinduced-Current Transient Spectroscopy A. P. Odrinskiœ Institute of Technical Acoustics, National Academy of Sciences of Belarus, pr. Lyudnikova 13, Vitebsk, 210717 Belarus e-mail: odra@mail333.com Submitted July 13, 2004; accepted for publication September 9, 2004 Abstract—Deep levels in semi-insulating CdS single crystals grown with a variation in the stoichiometric com- position are investigated by photoinduced-current transient spectroscopy (PICTS). A series of deep levels with a thermal activation energy ranging from 0.066–0.54 eV is revealed. It is found that the signal ratio in the set of spectra disagrees with the basic PICTS model. A procedure for evaluation of the concentration of deep levels is developed for these conditions. © 2005 Pleiades Publishing, Inc.