**1. Introduction**

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**5. References** 

Novel achievements of nano- and microelectronics are closely connected with working-out of new semiconductor materials. Among them the compounds II-VI (where A = Cd, Zn, Hg and B = О, S, Se, Te) are of special interest. Due to unique physical properties these materials are applicable for design of optical, acoustical, electronic, optoelectronic and nuclear and other devices [1-3]. First of all the chalcogenide compounds are direct gap semiconductors where the gap value belongs to interval from 0.01 eV (mercury chalcogenides) up to 3.72 eV (ZnS with zinc blende crystalline structure) As potential active elements of optoelectronics they allow overlapping the spectral range from 0.3 m to tens m if using them as photodetectors and sources of coherent and incoherent light. The crystalline structure of II-VI compounds is cubic and hexagonal without the center of symmetry is a good condition for appearing strong piezoeffect. Crystals with the hexagonal structure have also pyroelectric properties. This feature may be used for designing acoustoelectronic devices, amplifiers, active delay lines, detectors, tensile sensors, etc. [1-2]. Large density of some semiconductors (CdTe, ZnTe, CdSe) makes them suitable for detectors of hard radiation and –particles flow [4-5]. The mutual solubility is also important property of these materials. Their solid solutions give possibility to design new structures with in-advance defined gap value and parameters of the crystalline lattice, transmission region, etc. [6].

Poly- and monocrystalline films of II-VI semiconductors are belonging to leaders in field of scientific interest during the last decades because of possibility of constructing numerous devices of opto-, photo-, acoustoelectronics and solar cells and modules [2-5]. However, there are also challenges the scientists are faced due to structural peculiarities of thin chalcogenide layers which are determining their electro-physical and optical characteristics. The basic requirements for structure of thin films suitable for manufacturing various microelectronic devices are as follows: preparing stoichiometric single phase

© 2012 Kurbatov et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

monocrystalline layers or columnar strongly textured polycrystalline layers with low concentration of stacking faults (SF), dislocations, twins with governed ensemble of point defects (PD) [7-8]. However, an enormous number of publications points out the following features of these films: tend to departure of stioichiometric composition, co-existing two polymorph modifications (sphalerite and wurtzite), lamination morphology of crystalline grains (alternation of cubic and hexagonal phases), high concentration of twins and SF, high level of micro- and macrostresses, tend to formation of anomalous axial structures, etc. [2-3, 9]. Presence of different defects which are recombination centers and deep traps does not improve electro-physical and optical characteristics of chalcogenide layers. It restricts the application of the binary films as detector material, basic layers of solar energy photoconvertors, etc.

Thus, the problem of manufacturing chalcogenide films with controllable properties for device construction is basically closed to the governing of their defect structure investigated in detail. We will limit our work to the description of results from the examination of parameters of localized states (LS) in polycrystalline films CdTe, ZnS, ZnTe by the methods of injection and optical spectroscopy.

#### **1.1. Defect classification in layers of II-VI compounds**

Defects' presence (in the most cases the defects of the structure are charged) is an important factor affecting structure-depended properties of II-VI compounds [3, 5, 10]. Defects of the crystalline structure are commonly PD, 1-, 2-, and 3-dimensional ones [11- 12]. Vacancies (VA, VB), interstitial atoms (Ai, Bi), antistructural defects (AB, BA), impurity atoms located in the lattice sites (CA, CB) and in the intersites (Ci) of the lattice are defects of the first type. However, the antistructural defects are not typical for wide gap materials (except CdTe) and they appear mostly after ionizing irradiation [13-14]. The PD in chalcogenides can be one- or two-charged. Each charged native defect forms LS in the gap of the semiconductor, the energy of the LS is *∆Еi* either near the conduction band (the defect is a donor) or near the valence band (then the defect is an acceptor) as well as LS formed in energy depth are appearing as traps for charge carriers or recombination centers [15-16]. Corresponding levels in the gap are called shallow or deep LS. If the extensive defects are minimized the structure-depending properties of chalcogenides are principally defined by their PD. The effect of traps and recombination centers on electrical characteristics of the semiconductor materials is considered in [16]. We have to note that despite a numerous amount of publications about PD in Zn-Cd chalcogenides there is no unified theory concerning the nature of electrically active defects for the range of chalcogenide vapor high pressures as well as for the interval of high vapor pressure of chalcogen [13-14, 17-18].

Screw and edge dislocations are defects of second type they can be localized in the bulk of the crystalites or they form low-angled boundaries of regions of coherent scattering (RCS). Grain boundaries, twins and surfaces of crystals and films are defects of the third type. Pores and precipitates are of the 4th type of defects. All defects listed above are sufficiently influencing on physical characteristics of the real crystals and films of II-VI compounds due to formation of LS (along with the PD) in the gap of different energy levels [17-20].
