ISSN 1063-7826, Semiconductors, 2006, Vol. 40, No. 4, pp. 403–405. © Pleiades Publishing, Inc., 2006. Original Russian Text © V.P. Mygal, A.S. Phomin, 2006, published in Fizika i Tekhnika Poluprovodnikov, 2006, Vol. 40, No. 4, pp. 408–410. 403 The main problem of II–VI materials and the sen- sors based on them is the instability of characteristics, which is mainly caused by the presence of a variety of structural inhomogeneities in these materials. It has been shown that the reconstruction of the fields gener- ated in CdZnTe crystals by two-dimensional structural defects, namely, twins, mosaicity blocks, slip bands, etc., significantly affects the photosensitivity spectrum and in some cases leads to instability in certain spectral ranges [1, 2]. Therefore, it is reasonable to assume that this reconstruction is also accompanied by temporal and spatial instability. The present study is mainly aimed at verifying this assumption. We studied both the time-independent photocurrent as a function of the location of a monochromatic optical probe and the dynamic photoresponse to the pulsed Π-like photoexcitation for Cd 1 – x Zn x Te crystals (x = 0.1–0.2) grown by vertical crystallization from the melt under various conditions [3]. Gold or indium–gallium contacts were deposited onto the opposite largest faces of the samples that had resistivity ρ ~ (10 10 –10 11 ) Ω cm and were shaped as rectangular parallelepipeds 5 × 5 × 2 mm or 11 × 11 × 2 mm in size. The repetition rate of the monochromatic optical pulses varied in the range 0.01–1 Hz. The steady-state photocurrent spectra I = f(ν), where ν is the radiation frequency, and the dynamic photoresponse of the samples were measured in a field with the strength E = 10–10 4 V/cm using an electrometric transformer based on an AD795 opera- tional amplifier. The signal was digitized, and the data obtained were processed using a computer. We exam- ined the crystal quality of the samples by etching, infra- red microscopy, and modified shadow method. The crystal surface was scanned by a monochromatic opti- cal probe 50 μm wide using automated movement of the sample with the rates from 0.5 to 10 mm/min. To reveal the stable (attractors) and unstable photore- sponse cycles under Π-like photoexcitation, we studied the totalities of phase diagrams dI(t)/dt = f(I(t)), where t is time, which were obtained by monotonic heating and cooling of the samples according to [4]. Examinations showed that the diagrams dI(ν)/dν = f(I(ν)) constructed on the basis of the spectral depen- dences of the photocurrent I = f(ν) are the most appro- priate for analyzing the spectral stability of the CdZnTe crystals. These diagrams reflect the photocurrent spec- trum in the parametric form and involve closed sequences of arclike segments. In this case, the spectral ranges of unstable photoresponse with poor reproduc- ibility are observed in the diagrams dI(ν)/dν = f(I(ν)), obtained by sequential measurement of the photore- sponse spectra of the same sample under identical con- ditions. The number of spectrally unstable segments, which correlates with the structural quality, is larger for the samples containing a variety of structural inhomo- geneities. Therefore, it was interesting to examine the coordinate dependences of the photocurrent I(x), where x is the coordinate of location of the monochromatic probe, at the frequencies corresponding to the regions of spectral stability and instability. It turned out that these dependences are individual for all samples stud- ied and depend on the radiation frequency, which indi- cates that the fields induced by structural inhomoge- neities affect the character of the distribution of elec- trically active centers. In this case, the curves I(x) which were obtained at the frequencies corresponding to the stability regions of the diagrams dI(ν)/dν = f(I(ν)), are fairly reproducible during repeated scanning. However, three portions can be conventionally iso- lated in the dependences I(x) which correspond to the frequencies of spectral instability in these diagrams The Temporal and Spatial Instability of Photoelectric Response of the CdZnTe Crystals V. P. Mygal^ and A. S. Phomin^^ Zhukovsky National Aerospace University (KhAI), ul. Chkalova 17, Kharkov, 61070 Ukraine ^e-mail: mygal@mail.ru ^^e-mail: khai_physical_lab@xai.edu.ua Submitted August 15, 2005; accepted for publication September 14, 2005 Abstract—The spectral, temporal, and spatial instabilities of the photoelectric response I of CdZnTe crystals with a variety of structural inhomogeneities are revealed. It is shown that the character and interrelation of these instabilities are most pronounced in the diagrams dI(t)/dt = f(I(t)) and dI(ν)/dν = f(I(ν)), where ν is the fre- quency and t is time in which the processes accompanying the stability loss are clearly seen. PACS numbers: 72.40.+w, 61.72.Hh, 61.66.Fh DOI: 10.1134/S1063782606040063 ELECTRONIC AND OPTICAL PROPERTIES OF SEMICONDUCTORS