This PDF file contains the front matter associated with SPIE Proceedings Volume 8507, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Early CMOS SSPM pixel designs utilize a highly doped layer near the surface as a component for the Geiger junction, which limits the collection of charge from the surface and the UV response of the high gain solid state photodetector. To address these limitations, we are developing a new generation of CMOS SSPMs using pixel elements with a buried layer as a component of the Geiger junction in a process with smaller feature sizes. The new SSPM, an array of newly designed Geiger photodiode elements, is designed and fabricated to provide improvements in blue light response and dark noise performance. This work compares the performance of the early and new CMOS SSPM designs. Results showed ~2-4× improvement of detection efficiency in the blue/shallow UV region (350nm to 450nm), and a 10× reduction in detector dark count rate. Due to higher operating bias, the after pulse multiplier is no larger than a factor of 1.5 larger than the previous design. Inter-pixel cross-talk is similar to previous SSPM designs at comparable Geiger probabilities.

There are thousands of halides that are potentially useful as scintillator hosts. Establishing understanding of trends and fundamental mechanisms for energy transport is important for identifying those that are most likely to be useful. We report calculations of electronic structures in relation to energy transport and optical properties in halide scintillators. These include hybrid functional studies of rare earth activator energy levels, calculations of self-trapping energies of carriers, and electronic structures in relation to energy transport in elpasolites. We use the relationship between electronic structure and energy transport to suggest a path for identifying new high light output elpasolite scintillators. We also present the electronic structure for TlPbI3, which with activation is a potential low band gap scintillator.

The availability of large, single crystals of cadmium zinc telluride (CZT) with uniform properties is key to improving the performance of gamma radiation detectors fabricated from them. Towards this goal, we discuss results obtained by computational models that provide a deeper understanding of crystal growth processes and how the growth of CZT can be improved. In particular, we discuss methods that may be implemented to lessen the deleterious interactions between the ampoule wall and the growing crystal via engineering a convex solidification interface. For vertical Bridgman growth, a novel, bell-curve furnace temperature profile is predicted to achieve macroscopically convex solid-liquid interface shapes during melt growth of CZT in a multiple-zone furnace. This approach represents a significant advance over traditional gradient-freeze profiles, which always yield concave interface shapes, and static heat transfer designs, such as pedestal design, that achieve convex interfaces over only a small portion of the growth run. Importantly, this strategy may be applied to any Bridgman configuration that utilizes multiple, controllable heating zones. Realizing a convex solidification interface via this adaptive bell-curve furnace profile is postulated to result in better crystallinity and higher yields than conventional CZT growth techniques.

We present results of structural, electrical, and defect characterization of 4H-SiC epitaxial layers and bulk crystals and show performance of the radiation detectors fabricated from these materials. The crystal quality was evaluated by x-ray diffraction (XRD) rocking curve measurements, electron beam induced current (EBIC) imaging, and defect delineating etching in conjunction with optical microscopy and scanning electron microscopy (SEM). Studies of the electrically active intrinsic defects and impurities were conducted using thermally stimulated current (TSC) measurements in a wide temperature range of 94 - 750K. The results are correlated with the capability of bulk crystals and epitaxial layers for the detection of α-particles, low to high energy x-rays and gamma rays. High barrier rectifying Schottky diodes have been fabricated and tested. The epitaxial 4H-SiC radiation detectors exhibited low leakage current (< 1 nA) at ~ 200 V operating voltage up to 200 C. The soft x-ray responsivity measurements performed at the National Synchrotron Light Source (NSLS) at Brookhaven National Lab (BNL) showed significantly improved characteristics compared to commercially-available SiC UV photodiode detectors.

We demonstrate that mercury and antimony compounds with chalcogens (Q = S, Se, Te) and halogens (X = I, Cl, Br) can be a promising family for radiation detection materials. Chalcogen p-orbitals are usually located near the Fermi level and they are responsible for relative high mobilities but at the same time band gap decreases (from S to Te) due to their extended interactions. Halogens on the other hand have their bands well below the Fermi level and salts between transition metals and halogen are usually insulators. Incorporation of halogen atoms in a mercury or antimony chalcogenide framework can give rise to intermediate properties between the two end members (HgQ and HgX2), i.e. structures composed of heavy elements (Z < 40), wide band gap (1.6 - 2.5 eV), and high carrier mobilities. As a proof of concept, we will present two new chalcohalide families, Hg3Q2X2 and SbQX. Crystal growth of the Hg3Te2Br2 phase (7.8 g/cm3 and 2.5 eV) by a vapor transport method gave mm-sized single crystals with electrical resistivity values more in the GΩ.cm range. Preliminary data for mobility-lifetime products for both electron and hole carriers were around 10-5 cm2/V. SbSeI (5.8 g/cm3 and 1.7 eV) sample grown by relatively fast Bridgman technique showed an MΩ.cm range (2.8 x 106 Ω.cm) resistivity with a similar order of magnitude (10-4 cm2/V) of mobility-lifetime products for both electron and hole carriers.

The spectroscopic performance of two Frisch collar CdZnTe (CZT) detectors with different dimensions has been tested and evaluated after exposing to high energy gamma rays. The dimensions of one of the detectors, detector A, were 4.2×6.2×6.5 mm³ and that of detector B were 3.0×4.0×9.0 mm³. Detector grade CZT crystals were grown from zone refined Cd, Zn, and Te (~7N) precursor materials, using the tellurium solvent method. Detectors with virtual Frisch grid configuration were fabricated from these crystals. I-V measurements revealed low leakage currents at room-temperature, ~ 11 nA at 1100V for detector A and 14.5 nA at 1800V for detector B. For the spectroscopic measurements, the detectors were irradiated using a ¹³⁷Cs source. Detector A showed an impressive energy resolution of 1.4% and detector B showed an energy resolution of ~5.9 % for 662 keV from Cs-137 radioisotope. A digital technique based biparametric correlation study showed that the performance of detector B was limited by the operating bias voltage. Further, a digital correction scheme has been described and was applied to recover the effect of charge (electron) – loss.

In this paper, we report theoretical studies of native defects and dopants in a number of room-temperature semiconductor radiation detection materials, i.e., CdTe, TlBr, and Tl₆SeI₄. We address several important questions, such as what causes high resistivity in these materials, what explains good μτ product (carrier mobility-lifetime product) in soft-lattice ionic compounds that have high defect density, and how to obtain high resistivity and low carrier trapping simultaneously. Our main results are: (1) shallow donors rather than deep ones are responsible for high resistivity in high-quality detectorgrade CdTe; (2) large dielectric screening and the lack of deep levels from low-energy native defects may contribute to the good μτ products for both electrons and holes in TlBr; (3) the polarization phenomenon in Tl₆SeI₄ is expected to be much reduced compared to that in TlBr.

Experiments were performed with pure and doped lead halides to investigate growth conditions for large crystals. Direct observations during the growth of 25 mm diameter crystal growing at high velocities showed that torodial type instability is formed at the solid/liquid interface during the growth. These instabilities translate into point defects and line defects. We report the results of extensive experiments on Lead bromide doped with silver bromide to study double diffusive transport. Control of instability at the interface provides a great improvement in the quality of crystal more specifically point defects and line defects. The controlled doping controls the defects and polytypism, and hence reduces the cracking and production of very large diameter good quality crystal is possible by Bridgman method. Results on the quality as the function of convection and growth parameters are reported in this paper.

We report on the characterization of optical and electronic properties of a series of thallium chalcogenide, wide gap ternary semiconductor compounds including Tl6I4Se, Tl6I4S, Tl3SbS3, Tl2SnS3, and Tl7Bi3I16 for ionized radiation detection at the x-ray and γ ray regimes. The semiconductor crystals were grown by the modified Bridgman method. The optical absorption, band gap, mobility-lifetime products for electron and hole carriers were measured at room temperature. For Tl6I4S and Tl6I4Se the mobility-lifetime products are comparable to those of CdZnTe. We measured room temperature detector response to x-ray and γ ray sources. For 137Cs radiation, Tl6I4Se has a well-resolved spectral response comparable to that of CdZnTe.

Approach to obtaining of neutron detector material alternative to ³He containing ionization gas detectors is proposed. Recently, a severe deficit of the ³He has pushed its price up strongly, so alternative cheaper detecting materials are demanded. Possible alternatives to ³He are materials containing ¹⁰B and ⁶Li isotopes. These two elements form many inorganic materials, either crystalline or amorphous. Glass scintillators look very advantageous as detector materials, especially for large area detectors, as their manufacturing could be cheaper and easier-to-scale, compared to single crystals and ceramics. A poor exciton transport, which is a fundamental feature of glass scintillators, limits their light yield and, therefore, practical use. Here we discuss a possibility to improve energy transfer to luminescent centers by creation of high concentration of crystalline luminophore particles in the glass matrix. This could be achieved through the controlled crystallization of the glass. We demonstrate how this approach works in well known Li-Al-Si (LAS) glass system. Partially crystallized Ce³⁺-doped glass with nanocrystalline inclusions is obtained, which shows the superior scintillation properties compared to amorphous glass. The material is characterized by an emission spectrum shift towards shorter wavelengths, which provides low light self-absorption.

Hexagonal boron nitride (hBN) possesses extraordinary potential for solid-state neutron detector applications. This stems from the fact that the boron-10 (¹⁰B) isotope has a capture cross-section of 3840 barns for thermal neutrons that is orders of magnitude larger than other isotopes. Epitaxial layers of hBN have been synthesized by metal organic chemical vapor deposition (MOCVD). Experimental measurements indicated that the thermal neutron absorption coefficient and length of natural hBN epilayers are about 0.0036 μm^-1 and 277 μm, respectively. To partially address the key requirement of long carrier lifetime and diffusion length for a solid-state neutron detector, micro-strip metal–semiconductor–metal detectors were fabricated and tested. A good current response was generated in these detectors using continuous irradiation with a thermal neutron beam, corresponding to an effective conversion efficiency approaching ~80% for absorbed neutrons.

Experimental work performed in the area of neutron detector development at the Remote Sensing Laboratory-Andrews Operations (RSL-AO) sponsored by the U.S. Department of Energy, National Nuclear Security Administration (NNSA) in recent months is presented in this article. Ten pressurized He-3 tubes with an inch of annular polyethylene moderator around them are arranged to make an isosceles triangle with three fold symmetry. MCNPX simulation code has been used to obtain the angular response function of the detector array using a bare Cf-252 source. The neutron counts profile shows possibility of determining the angle of a near - field neutron source with adequate angular resolution for emergency response.

We have developed the detached Bridgman process for growth of CdZnTe crystals. Detachment of the solidification interface from the growth ampoule results in a low density of dislocations in the grown material and large single crystal grains. The detached Bridgman process also provides for direct control of the melt composition close to the growth front, allowing for accurate control of both the density of the Te/Cd precipitates as well as the majority carrier concentration in the grown material. The influence of melt-composition control and compensation by shallow and deep donors on detector performance is presented.

Results will be presented for the growth of CdZnTe by the low pressure Bridgman growth technique. To decrease deeplevel trapping and improve detector performance, high purity commercial raw materials will be further zone refined to reduce impurities. The purified materials will then be compounded into a charge for crystal growth. The crystals will be grown in the programmable multi-zone furnace (PMZF), which was designed and built at Northrop Grumman‟s Bethpage facility to grow CZT on Space Shuttle missions. Results of the purification and crystal growth will be presented as well as characterization of crystal quality and detector performance.

We have developed the detached Bridgman process for growth of CdZnTe crystals. Detachment of the solidification interface from the growth ampoule results in a low density of dislocations in the grown material and large single crystal grains. The detached Bridgman process also provides for direct control of the melt composition close to the growth front, allowing for accurate control of both the density of the Te/Cd precipitates as well as the majority carrier concentration in the grown material. The influence of melt-composition control and compensation by shallow and deep donors on detector performance is presented.

Different rotation profiles were applied to the ampoule during Vertical Bridgman (VB) growth of Cd0.9Zn0.1Te (CZT) for enhancing compositional homogeneity, minimizing radial and axial segregation and stabilizing growth interface. The radial Zinc (Zn) segregation was significantly minimized. Improvements in the axial Zn segregation were also noticeable. The modifications in interface shapes during the growth were prominent from the photoluminescence (PL) studies. Improved grain structure was observed with growths containing lower (0.5 wt. %) initial excess Te; however with higher amount of initial excess Te (7.5 wt. %) high resistivity ingots with improved carrier properties were grown consistently but with lower single crystal yield. With more intense rotations, resistivity values within the ingot varied by an order of magnitude showing non uniformity in distribution of dopants.

Room-temperature-operating CdZnTe radiation detectors have high energy resolution, linear energy response and are capable of operating in normal counting and spectroscopic modes, hence are highly desirable for medical diagnosis, nondestructive industrial evaluations, homeland security, counterterrorism inspections and nuclear proliferation detection to ensure national and international nuclear safety. HgTe/HgCdTe superlattices can be designed to selectively transport one carrier species while hindering transport of the other. Specifically, one designs a large carrier effective mass for undesired carriers in the electric field direction, which results in low carrier velocities, and yet a density of states for undesired carrier that is lower than that of a comparable bulk semiconductor, which results in low carrier concentrations, hence a low current density under an electric field. The opposite carrier species can be designed to have a large velocity and high density of states, hence producing a large current density. By employing HgTe/HgCdTe superlattices as contact layers intermediate between CdZnTe absorbers and metal contacts, leakage currents under high electric fields are reduced and improved x-ray and γ-ray detector performance is anticipated. Pixilated CdZnTe radiation detectors arrays were fabricated and characterized to evaluate the effectiveness of HgTe/HgCdTe superlattices in reducing leakage currents. Current-voltage characteristics show that HgTe/HgCdTe superlattice contact layers consistently result in significantly reduced leakage currents relative to detectors with only metal contacts.

Scintillator crystal detectors form the basis for many radiation detection devices. Therefore, a search for high light yield single crystal scintillators with improved energy resolution, large volume, and the potential for low cost, is an ongoing process that has increased in recent years due to a large demand in the area of nuclear isotope identification. Alkaline earth halides, elpasolites and rare earth halides are very interesting because many compositions from these crystal families provide efficient Ce3+/ Eu2+ luminescence, good proportionality and good energy resolution. They also have small band-gap leading to higher light yields. Ce3+and Eu2+ are efficient, and the emission wavelengths in the 350-500 nm region matches well with PMTs and a new generation of Siphotodiodes. In this presentation, we will the present progress made in the crystal growth of these compositions, and scintillator properties of large diameter SrI2:Eu2+ single transparent crystals. The crystals were grown successfully using the vertical Bridgeman technique. Crystals with different diameters of 1”, 1.3”, and 1.5” will be discussed. SrI2:Eu was discovered a half century ago, and was recently found to be an outstanding material for gamma ray-spectroscopy with high light yield, very good non-proportionality, and excellent energy resolution. We will also discuss growth and properties of larger Cs2LiYCl6 (CLYC) crystals. Recently, it has been shown that crystals from the elpasolite family, including CLYC, can be successfully employed for a dual gamma ray and neutron detection, which is possible with the help of pulse shape discrimination (PSD). PSD allows for recognition of an incident particle’s nature based on the shape of the corresponding scintillation pulse. CLYC has the potential to minimize the cost and complexity of dual sensing gamma ray and neutron spectrometers. We also address progress in growth of CLYC crystals with large diameters (1” and 2”) that are transparent and crack free.

Lanthanide gallium/aluminum-based garnets have a great potential as host structures for scintillation materials for medical imaging. Particularly attractive features are their high density, chemical radiation stability and more importantly, their cubic structure and isotropic optical properties, which allow them to be fabricated into fully transparent, highperformance polycrystalline optical ceramics. Lutetium/gadolinium aluminum/gallium garnets (described by formulas ((Gd,Lu)3(Al,Ga)5O12:Ce, Gd3(Al,Ga)5O12:Ce and Lu3Al5O12:Pr)) feature high effective atomic number and good scintillation properties, which make them particularly attractive for Positron Emission Tomography (PET) and other γ- ray detection applications. The ceramic processing route offers an attractive alternative to single crystal growth for obtaining scintillator materials at relatively low temperatures and at a reasonable cost, with flexibility in dimension control as well as activator concentration adjustment. In this study, optically transparent polycrystalline ceramics mentioned above were prepared by the sintering-HIP approach, employing nano-sized starting powders. The properties and microstructures of the ceramics were controlled by varying the processing parameters during consolidation. Single-phase, high-density, transparent specimens were obtained after sintering followed by a pressure-assisted densification process, i.e. hot-isostatic-pressing. The transparent ceramics displayed high contact and distance transparency as well as high light yield as high as 60,000-65,000 ph/MeV under gamma-ray excitation, which is about 2 times that of a LSO:Ce single crystal. The excellent scintillation and optical properties make these materials promising candidates for medical imaging and γ-ray detection applications.

A precise measurement of the Cosmic X-ray Background (CXB) is crucial for constraining models of the evolution and composition of the universe. While several large, expensive satellites have measured the CXB as a secondary mission, there is still disagreement about normalization of its spectrum. The Cosmic X-ray Background NanoSat (CXBN) is a small, low-cost satellite whose primary goal is to measure the CXB over its two-year lifetime. Benefiting from a low instrument-induced background due to its small mass and size, CXBN will use a novel, pixelated Cadmium Zinc Telluride (CZT) detector with energy resolution < 1 keV over the range 1-60 keV to measure the CXBN with unprecedented accuracy. This paper describes CXBN and its science payload, including the GEANT4 model that has been used to predict overall performance and the backgrounds from secondary particles in Low Earth Orbit. It also addresses the strategy for scanning the sky and calibrating the data, and presents the expected results over the two-year mission lifetime.

The Remote Sensing laboratory (RSL) of National Security Technologies Inc. has built an array of large (5.08 - cm x 10.16 – cm x 40.6 - cm) thallium doped sodium iodide (NaI: Tl) scintillators to locate and screen gamma-ray emitting radioisotopes that are of interests to radiological emergency responders [1]. These vehicle mounted detectors provide the operators with rapid, simple, specific information for radiological threat assessment. Applications include large area inspection, customs inspection, border protection, emergency response, and monitoring of radiological facilities. These RSL mobile units are currently being upgraded to meet the Defense Threat Reduction Agency mission requirements for a next-generation system capable of detecting and identifying nuclear threat materials. One of the challenging problems faced by these gamma-ray detectors is the unambiguous identification of medical isotopes like 131I (364.49 keV [81.7%], 636.99 keV [7.17%]), 99Tcm (140.51 keV [89.1%]) and 67Ga (184.6 keV [19.7%], 300.2 [16.0%], 393.5 [4.5%] that are used in radionuclide therapy and often have overlapping gamma-ray energy regions of interest (ROI). The problem is made worse by short (about 5 seconds) acquisition time of the spectral data necessary for dynamic mobile detectors. This article describes attempts to identify medical isotopes from data collected from this mobile detection system in a short period of time (not exceeding 5 secs) and a large standoff distance (typically ~ 10 meters) The mobile units offer identification capabilities that are based on hardware auto stabilization of the amplifier gain. The 1461 keV gamma-energy line from 40K is tracked. It uses gamma-ray energy windowing along with embedded mobile Gamma Detector Response and Analysis Software (GADRAS) [2] simultaneously to deconvolve any overlapping gamma-energy ROIs. These high sensitivity detectors are capable of resolving complex masking scenarios and exceed all ANSI N42.34 (2006) requirements for the identification of bare, shielded and multiple isotopes.

X-ray polarimetry promises to give qualitatively new information about high-energy astrophysical sources, such as binary black hole systems, micro-quasars, active galactic nuclei, and gamma-ray bursts. We designed, built and tested a hard X-ray polarimeter, X-Calibur, to be used in the focal plane of the InFOCμS grazing incidence hard X-ray telescope. X-Calibur combines a low-Z Compton scatterer with a CZT detector assembly to measure the polarization of 20−60 keV X-rays making use of the fact that polarized photons Compton scatter preferentially perpendicular to the electric field orientation; in principal, a similar space-borne experiment could be operated in the 5 − 100 keV regime. X-Calibur achieves a high detection efficiency of order unity.

We investigated the influence of the ratio of the electron and hole mobility-lifetime products, (μτ)e,h and (μτ)e/(μτ)h, on the resolution of CdZnTe planar radiation detectors via Monte-Carlo simulations. Preliminary results show that this ratio exercises a larger effect than that of any other parameter on the detector’s peak-to-valley ratio and resolution. We determined the range of values of the ratio (μt)e/(μτ)h where the fast degeneration of the photopeak in CdZnTe detectors takes place at a gamma-ray energy 661.7 keV (137Cs). We offer an explanation, based on the results of some of our experimental data, on the spectrometric performance of CdZnTe detectors.

Manganese-doped A2(1-x)MnxB6 diluted magnetic semiconductors have recently attracted a great attention as a new class of semiconductors, because they exhibit an interesting combination of magnetic and semiconductor properties. Zn1-xMnxTe films were deposited by the closed space vacuum sublimation method on the glass substrates. Particle induced X-ray emission method was applied for determination of the film chemical composition. Structural investigations of the films were performed using X-ray diffractometer with CuKα radiation. The obtained results enabled to determine the effect of the growth conditions on the main structural parameters (lattice parameters, SDS, microdeformation levels) and chemical compositions of the films.

In work the complex investigation of structural and optical properties of CdTe and Cd1-xMnxTe semiconductor films deposited by close-spaced vacuum sublimation method using thermal evaporation on non-oriented substrates was carried out. The structural and phase analysis of the layers condensed at different substrate temperatures was performed.

We evaluated the effect of high-temperature treatment of Cd0.9Zn0.1Te:In single crystals using Hall-effect measurements, medium- and high-temperature annealing under various deviations from stoichiometry, and infra-red (IR) transmission microscopy Annealing at ~730 K sharply increased the electrical conductivity (by ~1-2 orders-of-magnitude). Plots of the temperature- and cadmium-pressure dependences of the electrical conductivity, carrier concentration, and mobility were obtained. Treating previously annealed Cd-samples under a Te overpressure at 1070 K allowed us to restore their resistance to its initial high values. The main difference in comparing this material with CdTe was its lowered electron density. We explained our results within the framework of Kröger’s theory of quasi-chemical reactions between point defects in solids.

We developed radiation-hard diamond detectors for registering intense fields of high energy electrons and X-rays, and monitoring the mode of operation of electron accelerators. After synthesizing a diamond film of detection quality up to 350-microns thick by chemical vapor deposition (CVD), we analyzed it by infra-red spectroscopy. We also developed techniques for heat treatment of the film, chemical etching, substrate removal, contact application, and priming by an exposure to X-rays and electrons. This work supported the production of detectors with a specific resistance of 10¹⁴Ohm×cm. The dependence of the detector signal’s amplitude on the displacement voltage was investigated under exposure to a direct electron beam with a current ranging from 660 to 930 mA. The duration of the leading edge of a detector pulse was 5 μs. Experiments also were undertaken on the registration by diamond detectors of Bremsstrahlung radiation with an end-point energy of 9 to 70 MeV. We also evaluated the dependence of the amplitude of the detector’s signal on the displacement voltage. Our comparison of detectors’ physical properties and detectors’ response to alphaparticle irradiation before and after the exposure to the accelerator beam showed no degradation, even after the absorbed dose exceeded 11.5 MGy.

The Cd_1-xZn_xTe (x = 0.1) crystals from two different manufacturers were studied by photoconductivity (PC) measurements. The samples 1 and 2 were subjected to chemical etching and irradiation with nanosecond laser pulses. The IR transmittance spectra of the crystals before and after laser irradiation were also monitored. The PC spectrum of the sample 1 had a typical one-band shape while the spectrum of the sample 2 exhibited two bands roughly corresponding to the bandgaps of CdTe and Cd_1-xZn_xTe that could be attributed to inhomogeneities in the surface region of the crystal. The positions of the maximum and red edge of the PC spectra did not correspond to the component compositions x in the bulk of Cd_0.9Zn_0.1Te crystals, however chemical polishing etching of the samples in a brominemethanol solution or/and laser irradiation led to this correspondence. Moreover, depending of laser pulse energy density, irradiation of Cd_1-xZn_xTe crystals resulted in a short-wavelength shift of the PC spectra, transformation of two bands to one in the case of the sample 2, and an increase in the photosensitivity of the semiconductor. The laser processing provided equalization of parameters in the surface and bulk regions.

Photoluminescence and optical properties of the surface functional layer of detector-grade Cl-compensated semiconductor CdTe(111) single crystals modified by chemical etching and nanosecond laser processing have been studied. A bromine-methanol solution was used for polishing etching and nanosecond pulses of the second harmonic of YAG:Nd laser was applied as a radiation source. The photoluminescence spectra were excited at 80 K by an argon-ion laser with wavelength of 488 nm. The intrinsic emission band at 1.56 eV and broad defect band peaked at 1.45 eV were observed in the spectra before and after chemical and laser processing of CdTe crystals. The emission between 1.4-1.5 eV was associated with carrier recombination at defects in the surface region, so called the band of surface states. The optical parameters were determined using an ellipsometer with laser wavelength of 632.8 nm. Refraction n and absorption k indices were calculated within model of a homogeneous absorbing surface layer upon an absorbing substrate. An increase in n and k was observed at laser irradiation with energy density near or higher than the CdTe melting threshold that was attributed to an increase in volume fraction of Te in the surface region of the crystal. A decrease in the emission intensity at 1.45 eV was evidence of a reduction of the surface impurity contribution to the spectrum as a result of chemical etching. A rise of this band after irradiation was due of formation of point defects and dislocations in a surface layer of the crystal.