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We report on the preparation, structure and scintillation properties of single crystal cesium hafnium chloride bromide (Cs2HfCl4Br2 or CHCB). The crystals were grown using a vertical Bridgman technique process. Single crystal X-ray diffraction showed that the as grown CHCB crystal structure was isostructural to Cs2HfCl6 crystals exhibiting the cubic K2PtCl6 –type crystal structure. The Cs2HfCl6−x - Cs2HfBrx system is a solid solution with the lattice parameter of Cs2HfCl6−xBrx increasing linearly with x in the range 0

The crystal growth and behavior of a high-performance, non-hygroscopic scintillator, Cs 2 HfCl 6 (CHC) and its variant, Cs 2 HfCl 4 Br 2 (CHCB) are presented in this work. CHC and CHCB were prepared by melt compounding of sublimed HfCl 4 with CsCl and CsBr to produce material for Bridgman growth. The resulting 1 cm dia. and 1 in. dia. CHC crystals showed in certain parts evidence of CsCl as a secondary phase—a result of a non-stoichiometric (CsCl-rich) melt composition caused by the high vapor pressure of HfCl 4 during compounding. This was verified using micro X-ray fluorescence spectrometry. There is also evidence of a secondary phase in CHCB, which has been presented for the first time. A clear CHC sample had a light yield and energy resolution of 30,000 ph/MeV and 3.3%, respectively, and decay components of 0.39 and 3.9 µs. A sample of CHCB with a secondary phase present in the core had a light yield and energy resolution of 18,600 ph/MeV and 4.4%, and with decay components of 0.38 and 2.0 µs for CHCB. Both crystals showed minimal moisture sensitivity.

Lithium containing chalcogenide single crystals have become very promising materials for photonics and radiation detection. Detection applications include nuclear nonproliferation, neutron science, and stellar investigations for the search of life. Synthesis and single crystal growth methods for lithium containing chalcogenide, specifically LiIn 1− x Ga x Se 2 , single crystals are discussed. This study elucidates the possibility of improving neutron detection by reducing the indium capture contribution; with the incorporation of the lithium-6 isotope, gallium substitution may overcome the neutron detection efficiency limitation of 6 LiInSe 2 due to appreciable neutron capture by the indium-115 isotope. As a figure of merit, the ternary parent compounds 6 LiInSe 2 and 6 LiGaSe 2 were included in this study. Quality crystals can be obtained utilizing the vertical Bridgman method to produce quaternary compounds with tunable optical properties. Quaternary crystals of varying quality depending on the gallium concentration, approximately 5×5×2 mm 3 or larger in volume, were harvested, analyzed and revealed tunable absorption characteristics between 2.8–3.4 eV.

In this paper the growth of a 16mm diameter Ce-doped Tl$_2$NaYCl$_6$ and its characterization as a gamma-ray detector are reported. With a 16 mm dia. x 8 mm cylindrical sample, energy resolution of 4.1% (FWHM) at 662 keV and light yield of 27,800ph/MeV are measured. Decay times of 91 ns (34%), 462 ns (52%), and 2.1 microseconds (15%) are calculated. The x-ray excited emission spectrum exhibits bands that are similar to other Tl-based elpasolite scintillators like Tl$_2$NaYCl$_6$:Ce., arXiv admin note: text overlap with arXiv:1911.03611

Strontium iodide (SrI 2 ), an important new scintillator crystal having a high light yield and excellent energy resolution, was grown for the first time by the edge-defined film-fed (EFG) growth method. Using high purity starting materials and floating dies made of graphite, fused quartz or AlN, large cylindrical, planar or square cross-section single crystals (12–15 mm across and >7 cm long) were produced at growth rates up to 15 mm/h, significantly faster than the current Bridgman growth technology. Details on the equipment used to grow this deliquescent material and on its growth behavior are given along with some discussion of crystalline quality.

We grew CdTe x Se 1− x crystals with nominal Se concentrations of 5%, 7%, and 10% by the vertical Bridgman technique, and evaluated their compositional homogeneity and structural quality at the NSLS’ X-ray fluorescence and white beam X-ray topography beam lines. Both X-ray fluorescence and photoluminescence mapping revealed very high compositional homogeneity of the CdTe x Se 1− x crystals. We noted that those crystals with higher concentrations of Se were more prone to twinning than those with a lower content. The crystals were fairly free from strains and contained low concentrations of sub-grain boundaries and their networks.

The re-discovery of Cs2HfCl6 (CHC) as a scintillator has lately generated much interest in this material and its family, which belongs to the K2PtCl6 cubic crystal structure [1] . CHC is an intrinsic scintillator that is non-hygroscopic, has no self-radioactivity, provides good energy resolution, and has good non-proportionality. In this paper we are reporting growth and scintillation properties of two new and Tl-, Hf- and Zr-based compounds of Tl2HfCl6 and Tl2ZrCl6, with physical densities of 5.1 g/cm3 and 4.5 g/cm3, respectively and effective atomic numbers (Zeff) of 71 and 69, respectively. Samples from successfully grown 16 mm diameter boules were cut, processed, and characterized for their scintillation and radiometric properties. Energy resolutions of 3.7% (FWHM) for THC and 3.4% for TZC (FWHM) at 662 keV are measured. Primary luminescence decay times of 1.1 μs and 2.3 μs, for Tl2HfCl6 and Tl2ZrCl6, respectively, as well as good proportionality for both materials have been observed.

Crystals of CuGaS2 and AgGaS2 with different isotopic compositions have been grown by chemical vapor transport (CVT) using iodine as the transport agent. Before performing the CVT growth, sulfur and copper were purified by sublimation and etching, respectively. 109Ag and the etched 71Ga isotopes were purified from oxides by vacuum annealing. Transparent yellow orange crystals of CuGaS2 and greenish yellow crystals of AgGaS2 were obtained in the shape of platelets, chunks, rods and needles in sizes of up to 8 mm (CuGaS2) and 30 mm (AgGaS2). These crystals were used to study their electronic, vibrational and thermodynamic properties. Higher excitonic states (n=2,3) were observed at low temperatures with wavelength-modulated reflectivity spectroscopy, thus proving an excellent surface and crystal quality. In addition, the experimentally determined non-monotonic temperature dependence of the excitonic energies can be well fitted by using two Bose–Einstein oscillators and their statistical factors, corresponding to characteristic acoustic and optical phonon frequencies. Isotopic shift of excitonic energies has also been successfully observed in these crystals.

Lithium containing semiconductor-grade chalcogenide single crystals were grown using the vertical Bridgman method. The source material was synthesized from elementary precursors in two steps, (i) preparing the metal alloy LiIn or LiGa, and (ii) reaction with chalcogen – Se or Te. In a number of experiments, enriched 6 Li isotope was used for synthesis and growth. The composition and structure of the synthesized materials was verified using powder X-Ray diffraction. The energy band gaps of the crystals were determined using optical absorption measurements. The resistivity of LiInSe 2 and LiGaSe 2 , obtained using current–voltage measurements is on the order of 10 8 –10 11 Ω cm. Photoconductivity measurement of a yellow LiInSe 2 sample showed a peak in the photocurrent around 445 nm. Nuclear radiation detectors were fabricated from single crystal wafers and the responses to alpha particles, neutrons and gammas were measured and presented. It suggests that this material is a promising candidate for neutron detection applications.

Crystal growth of bulk cadmium telluride (CdTe) ingot with 64 mm diameter and 75 mm height was accomplished in a modified vertical Bridgman configuration with the aim of achieving minimal nonstoichiometry related second phases (SP) defects such as inclusions and precipitates. As-grown crystal wafers were characterized with respect to infrared microscopy, bulk resistivity, low-temperature photoluminescence (PL) and foreign impurity concentration. Except for grain boundaries and twins, the wafers were found to be completely free of SP of sizes >1 μm and the distributions at different parts of the grown boule were found to be identical. Star shaped inclusions were observed at some places near the mid-section of the ingot, which were tentatively identified as Cd inclusions. At room temperature, the crystal exhibited high bulk resistivity values of 10 7 –10 8 Ω cm, which was found to be in conformity with the low density of nonstoichiometric defects. GDMS results indicated that the concentration of unintentional impurities was low enough for the electrical behavior to be explained uniquely on the basis of native defects.

Large diameter Bridgman growth of europium activated strontium iodide SrI 2 :Eu 2+ produces crystals with light yield of up to 115,000 ph/MeV with an excellent light yield proportionality. SrI 2 :Eu 2+ exhibits an outstanding energy resolution of better than 3% FWHM at 662 keV. Its emission is centered at 435 nm. The scintillation decays with a 1 μs time constant for small samples and up to 5 μs to larger crystals. This paper presents successful progress made in the vertical Bridgman crystal growth of SrI 2 :Eu 2+ and its scintillator properties. Large diameter, crack-free and transparent SrI 2 :Eu 2+ single crystals with diameters of 1 in., 1.3 in., 1.5 in. and 2 in. were all successfully grown.

Lithium containing A I B III C VI semiconductors are being considered as alternative materials for room temperature neutron detection. Materials such as LiGaSe 2 have been synthesized for non-linear optical applications; however, when the crystal is grown enriched in the 6 Li isotope, it is possible to imagine a radiation detector. A nuclear reaction occurs with 6 Li, which can be detected within the semiconductor crystal. As such, high quality crystals are required, which have few defects which prohibit charge collection. One of the primary challenges in growing a high quality crystal is the reactivity of lithium metal. Vacuum purified lithium metal was therefore reacted with gallium to form LiGa as an intermediate to LiGaSe 2 synthesis. Vertical and horizontal Bridgman growth was then conducted to determine the optimal growth conditions. Vertical Bridgman growth resulted in more pure crystals. Annealing in lithium metal vapor reduced crystal defects and improved optical and electrical properties of the subsequent LiGaSe 2 crystal.

Our review offers an overview of the Traveling Heater Method (THM) for growing crystals of CdZnTe, the most important semiconductor material available today for fabricating nuclear detectors operable at room temperature. The review compares the advantages of the THM technique with respect to melt growth techniques, and details the development and improvements in the technique from its start to the present day. It is known that the optimization of the growth parameters is highly dependent on the height of the Te-rich CZT molten zone, which in turn governs the shape of the growth interface. Special attention is paid to understand the effect of the Te-rich CZT molten zone on the growth interface (both microscopic and macroscopic) to improve the uniformity and overall quality of the grown crystals. We conclude that this technique affords us the best method today for consistently producing large homogenous detectors in mass quantities with a thickness up to 15 mm. Such detectors are need for many national-security and medical-imaging applications.

We present a review on mercuric iodide technology for room temperature gamma radiation detection. After four decades of research and development the material is attractive for a number of applications for x-ray and gamma-ray imagers with performances that match all competing materials. The crystal growth of large single crystals is challenging; however the high resistivity of 1013 Ω cm, the undoped, as-grown crystals and the high radiation damage remaining features that are not exhibited by any other wide bandgap semiconductor materials.

Single-crystal strontium iodide (SrI2) doped with relatively high levels (e.g., 3 - 6 %) of Eu2+ exhibits characteristics that make this material superior, in a number of respects, to other scintillators that are currently used for radiation detection. Specifically, SrI2:Eu2+ has a light yield that is significantly higher than LaBr3:Ce3+ -a currently employed commercial high-performance scintillator. Additionally, SrI2:Eu2+ is characterized by an energy resolution as high as 2.6% at the 137Cs gamma-ray energy of 662 keV, and there is no radioactive component in SrI2:Eu2+ - unlike LaBr3:Ce3+ that contains 138La. The Ce3+-doped LaBr3 decay time is, however, faster (30 nsec) than the 1.2 sec decay time of SrI2:Eu2+. Due to the relatively low melting point of strontium iodide (~515 oC), crystal growth can be carried out in quartz crucibles by the vertical Bridgman technique. Materials-processing and crystal-growth techniques that are specific to the Bridgman growth of europium-doped strontium iodide scintillators are described here. These techniques include the use of a porous quartz frit to physically filter the molten salt from a quartz antechamber into the Bridgman growth crucible and the use of a bent or bulb grain selector design to suppress multiple grain growth. Single crystals of SrI2:Eu2+ scintillators withmore » good optical quality and scintillation characteristics have been grown in sizes up to 5.0 cm in diameter by applying these techniques. Other aspects of the SrI2:Eu2+ crystal-growth methods and of the still unresolved crystal-growth issues are described here.« less

A transient, coupled model has been developed to analyze the segregation of zinc in cadmium zinc telluride (CZT) grown in an electrodynamic gradient freeze (EDG) furnace. The coupled model consists of a local model that solves for time-dependent melt flow, heat transfer, melt–crystal interface position, and zinc distribution in both melt and solid phases and a quasi-steady-state global model that features realistic furnace heat transfer. After verification and validation tests, the model is applied to predict composition patterns in a large-scale CZT EDG growth system previously analyzed by Gasperino et al. [On crucible effects during the growth of cadmium zinc telluride in an electrodynamic gradient freeze furnace, J. Crys. Growth 311 (2009) 2327–2335]. Surprisingly, anomalous zinc segregation is predicted, featuring a non-monotonic axial concentration profile and several local minima and maxima across the boule. A mechanistic explanation is put forth based on the cumulative effect of changes in multi-cellular melt flow structures, a particularly susceptible occurrence for CZT systems. Additional effects of furnace translation rate and solid state diffusion are probed.

AgGaxIn1−xSe2 single crystals with x=0.4 have been grown by the horizontal Bridgman technique for nonlinear optical application requires phase matching. High purity polycrystalline synthesis of AgGaxIn1−xSe2 was carried out at 850 °C, which is a relatively lower temperature compared to those in earlier reports, thus reducing secondary phase formation. An average Ga:In ratio of 62:38 (±3%) was measured using energy dispersive spectroscopy (EDS). As grown, a single crystal shows very high IR transmission of ∼65% in the spectral range of 4000–600 cm−1. There was no significant change in its IR transmission after annealing it at 500 °C for 20 days in vacuum in the presence of AgGaxIn1−xSe2 powder. This indicates a low concentration of defects in the crystal. The results demonstrate that the improved new synthesis method for crystal growth was promising and that the quality of the crystal was good.

We report the scintillation properties of both KPb 2 Cl 5 and K 2 CeCl 5 grown by vertical Bridgman method from synthesized and zone refined material. Both crystals exhibit minimal hygroscopic properties, which is desirable in applications where hermitization is not feasible. The KPb 2 Cl 5 crystal, doped with 2.5 mol% of EuCl 2 , appeared yellow in color and did not scintillate, while the self activated transparent K 2 CeCl 5 did. The energy resolution and decay time at 662 keV were measured to be 6.1% and 78 ns respectively, with a light yield of 31,000 photons/MeV.

We have developed a procedure to purify, synthesize and grow InI single crystals using the Bridgman technique. The commercial product of InI from Alfa Aesar (99.998% InI or 4 N) was zone refined by 50 passes of a zone-heater at 420 °C, traveling at 2 cm/h (the melting point of InI is 360 °C). InI was also synthesized using high purity In and I 2 by vapor transport technique. The grown InI single crystal showed a clear band edge excitonic emission around 2.02 eV at 6 K using photoluminescence measurement. The resistivities of InI detectors were found to be ∼2×10 9 and 1×10 8 Ω cm for zone refined and vapor synthesized starting materials, respectively. The InI detector formed by Pd–Pd contact showed clear peak of alpha particle detection at room temperature using 241 Am source.

This work focuses on the 3. Resultsanddiscussioncharacterization of 10×10×10 mm 3 THM-grown CdZnTe detector-grade crystals that have been post-growth annealed to remove the secondary phases (SPs). All three detectors showed an average energy resolution of ∼1.63% for a small guarded pixel with 3.5 mm diameter, measured using 137 Cs—662 keV with an average peak-to-Compton ratio of 2.7. The characterization showed vestiges of SPs and micro-twins present in some of the crystals indicating that the SPs prior to annealing were large and had size in the range of 100–500 μm. The various detectable structural features, such as micron twins, strains and sub-micron level of Te inclusions seemed to have little or no influence in the radiation spectrometer performance of the detectors; this is possibly because they are either having low density or electrically inactive.

The concentration, size and spatial distribution of Te inclusions in the bulk of CdMnTe crystals mined from two batches of ingots were studied. An isolated planar layer decorated with Te inclusions was identified in CdMnTe crystals from the second ingot. The internal electric field of a CMT crystal was probed by infrared (IR) imaging employing Pockels electro-optic effect. The effect of an isolated plane of Te inclusions on the internal electric-field distribution within the CdMnTe crystal was studied. Space charge accumulation around the plane of Te inclusions was observed, which was found to be higher when the detector was reverse-biased. The effects of the plane of Te inclusions on the electric-field distribution within the CdMnTe crystal, and the quality of CdMnTe crystals for nuclear detector applications are discussed.

Cesium cerium bromide (Cs2CeBr5) and potassium cerium bromide (K2CeBr5) are new scintillator materials for X-ray and gamma ray detector applications. Recently halide scintillator materials, such as Ce doped lanthanum bromide has been proved to be very important material for the same purpose. These materials are highly hygroscopic; a search for high light yield non-hygroscopic materials was highly desirable to advance the scintillator technology. In this paper, we are reporting the crystal growth of novel scintillator materials, cesium cerium bromide (Cs2CeBr5) and potassium cerium bromide (K2CeBr5). Crystals were successfully grown from the melt using the vertical Bridgman-Stockbarger technique, in a comparison with the high performance LaBr3 or LaCl3 crystals, cerium based alkali halides crystals, (Cs2CeBr5) and (K2CeBr5) have similar scintillation properties, while being much less hygroscopic. Furthermore, cesium based compounds will not suffer from the self-activity present in potassium and lanthanum compounds. However the Cs2CeBr5 crystals did not grow properly probably due to non-congruent melting or to some phase transition during cooling. Keywords." Scintillator materials; Ce3+; Energy resolution; Light yield; K2CeBr5

Ternary Hg 1− x Cd x I 2 ( 0 x 60 ) crystals were directionally solidified under ∼20 atm of argon pressure. For 0 x 0.17 , the crystals have the same red color as pure α-HgI 2 . For x > 0.17 the crystals are yellow. In the full compositional range 0 x 60 , the lattice is tetragonal, as in pure α-HgI 2 . The yellow crystals have a higher crystalline perfection and degrade less than the red crystals during sample preparation by cleaving and thus may be more suitable for fabrication required for X- and γ-ray detectors.

CdS0.8Se0.2 crystals doped with Cr2+ at a level of ∼1.2×1018 ions/cm3 were grown by the self-seeded physical vapor transport technique in vertical configuration. The ternary compound was synthesized from a stoichiometric mixture of vacuum sublimed CdS and CdSe. The growth temperature was 950°C and it produced a single crystal free of cracks and precipitates. The absorption peak maximum for Cr2+ ion was found to be at 1.85 μm and its intensity was used to determine the dopant concentration and its axial distribution. The axial and radial uniformity of the S/Se ratio were determined by energy dispersive X-ray spectroscopy and found to be uniform throughout the ingot and practically identical to the composition of the source.

We have employed photoluminescence mapping at room temperature of detector grade CZT grown by modified Traveling Heater Method (THM) technique and estimated the spatial variation of Zn composition. The composition was found to be fairly uniform over the major portion of the ingot length except near the conical part of the ingot and the upper part of the ingot. Unlike Bridgman growth technique, no detectable striations were observed. The composition was within ±0.3% over the length little more than 4 cm of the ingot. The growth interface revealed from the composition mapping was found to be reasonably flat.

Optical absorption spectra of the vapor phase over HgI2(s,l) were measured at sample temperatures between 349 and 610 K for wavelengths between 200 and 600 nm. The spectra show the samples sublimed congruently into HGI2 without any observed Hg or I2 absorption spectra. The Beer's Law constants for 15 wavelengths between 200 and 440 nm were derived. From these constants the vapor pressure of HgI2, P, was found to be a function of temperature for the liquid and the solid beta-phases: ln P(atm) = -7700/T(K) + 12.462 (liquid phase) and ln P(atm) = -10150/T(K) + 17.026 (beta-phase). The expressions match the enthalpies of vaporization and sublimation of 15.30 and 20.17 kcal/mole respectively, for the liquid and the beta-phase HgI2. The difference in the enthalpies gives an enthalpy of fusion of 4.87 kcal/mole, and the intersection of the two expressions gives a melting point of 537 K.

Carbon nanotubes (CNT) were synthesized using thermal chemical vapor deposition. The diameters of these CNT were quite uniform with the length of the CNT up to several tens of micrometers. With the substrate surface normal either along or against the gravity vector, different growth orientations of CNT were observed by scanning electron microscopy. The Raman spectra were similar for samples synthesized at different locations. These results suggest that gravity affects the growth of long CNT with small diameters.

Characterization studies of Cd1−xZnxTe (0

We report the investigation by photoluminescence lifetime measurements of the near-IR emissions from a series of chromium-doped ZnSe samples, correlated to their preparation conditions. The samples were polycrystalline or single crystals prepared by post growth diffusion doping or single crystals doped during growth by the physical vapor transport method. Room temperature lifetime values between 6 and 8 μs were measured for samples with Cr 2+ concentrations from low 10 17 to high 10 18 cm -3 range. Lifetime data taken down to 78 K was found to be rather temperature independent, reconfirming previous reports indicating a quantum yield of the corresponding emission of close to 100% at room temperature. A strong decrease in the room temperature lifetime was found for chromium concentrations higher than 10 19 cm -3 .

The preparation and thermophysical properties of AgGaTe 2 crystals are reported. The synthesis from pure elements was performed in a rocking oven and scanning electron microscopy and energy dispersive X-ray elemental analysis show the presence of additional phases. From simultaneous differential calorimetry and thermogravimetric analysis (SDT) measurements we have found that AgGaTe 2 melts at 725.7°C, with a heat of fusion of 104.8 J/g −1 . High temperature powder X-ray diffraction data confirmed the chalcopyrite structure and yielded the thermal expansion coefficients along the a - and c- axes to 500°C. Heating above that temperature, under inert gas flow, causes the material to sublime incongruently and produce a film of gallium rich surface. Experimental values of thermal diffusivity and estimates of the thermal conductivity values are also presented.

Mercuric iodide platelets were grown in the HgI 2 –HI–H 2 O system by solvent evaporation at constant temperature. Different solution temperatures, growing times and stirring conditions were studied. In order to determine the best growing parameters the chemistry of the HgI 2 –HI–H 2 O system was studied. Complexes [HgI 3 ] − and [HgI 4 ] −2 were identified and quantified in the solution by visible and UV spectrometry, according to the R ratio ([HgI 2 ]/[HI]). Solution oxidation and I 3 − interference were eliminated performing growth in high purity Argon atmosphere. Good mercuric iodide platelets, up to 6.0×7.0×1.5 mm 3 in size, were obtained with appropriate argon flow, temperature and growing time, for several independent experiences. Platelets were observed by optical microscopy and the absence of possible dislocations was confirmed by studying etch pits density after etching with ethanol–trichloroethylene. Non-existence of occluded water and hydrocarbons was confirmed by Fourier transform infrared spectroscopy and was related to results obtained for mercuric iodide crystals grown by the physical vapor transport method. Detectors were made with the platelets and their apparent resistivity, current density and X-ray performance were measured. Discussions about future improvements of growing mercuric iodide platelets in the HgI 2 –HI–H 2 O system and comparison of this method with others are included.

Solid-state tunable laser sources in the mid-IR region have been recently investigated for their potential in remote sensing applications. Room temperature lasers based on single crystals of chromium-doped CdSe are particularly interesting due to their broad band tunability beyond 2 lm spectral region. In this study, we have grown doped single crystals by the high-temperature gradient freezing solution technique, using selenium as the solvent. Crystals of 1.2 cm in diameter and up to 7 cm long, cracks and precipitates free could be obtained. The e!ective segregation coe$cient of Cr2‘ ions along the ingot was evaluated. Room temperature emission lifetime values of 3.0}4.5 ls were measured. ( 2000 Published by Elsevier Science B.V. All rights reserved.

Cr-doped ZnSe single crystals were grown by self-seeded physical vapor transport technique under both vertical (stabilized) and horizontal configurations. The source materials were mixtures of ZnSe and CrSe. The growth temperatures were in the range of 1140 to 1150C and the furnace translation rates were 1.9 to 2.2 mm/day. The surface morphology of the as-grown crystals was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The different features on the as-grown surface of the vertically and horizontally grown crystals suggests that different growth mechanisms were involved for the two growth configurations. The [Cr] doping levels were determined to be in the range of 1.8 to 8.3 x 10(exp 19)/cubic centimeter from optical absorption measurements. The crystalline quality of the grown crystals were examined by high resolution triple crystal X-ray diffraction (HRTXD) analysis.

Cadmium manganese telluride (Cd 1− x Mn x Te) is a diluted magnetic semiconductor material which forms the basis for many important devices such as IR detectors, solar cells, magnetic field sensors, optical isolators, and visible and near IR lasers. High resistivity (>10 10 Ω cm) and high μ τ (>10 −6 cm 2 /V) material, which are the two prerequisites in the fabrication of radiation detectors, has recently been demonstrated at Brimrose Corp. This paper presents the crystal growth of intentionally vanadium doped crystals, the surface preparation and contacting procedure, as well as the best detector performance obtained so far. Dark current characteristics, and low temperature photoluminescence results are also presented and discussed.

CdTe crystals were grown by horizontal seeded physical vapor transport technique in uncoated and boron nitride coated fused silica ampoules with the source materials near the congruent sublimation condition. The grown crystals were characterized by current-voltage measurements, low temperature photoluminescence spectroscopy, near IR transmission optical microscopy, spark source mass spectroscopy and chemical etching. The measured resistivities of the crystals were in the high-10(exp 8) ohm-cm range. Although the crystal grown in the boron nitride coating was contaminated with boron from the photoluminescence measurements, the coating yielded a single crystal with no inclusions or precipitates.

Crystals of Cd(1-x)Zn(x)Te with x = 0.2 and 40 g in weight were grown on monocrystalline cadmium-zinc telluride seeds by closed-ampoule physical vapor transport with or without excess (Cd + Zn) in the vapor phase. Two post-growth cool-down rates were used. The crystals were characterized using low temperature photoluminescence, atomic force microscopy, chemical etching, X-ray diffraction and electrical measurements. No formation of a second, ZnTe-rich phase was observed.

In this study, the photoluminescent and electric properties of as-grown CdS crystals and the effects observed after post-growth annealing in a cadmium, sulphur, and selenium overpressure were investigated. Bulk CdS crystals were grown by physical vapor transport (PVT) from high-purity starting materials, and two types of as-grown crystals, one "dark" and the other "clear" were obtained both having a medium resistivity of 106-108 l)-cm. The "dark"-type crystals are cadmium rich, as evidenced by an emission peak centered around 2.07 eV, which may be attributed to sulphur vacancies, while in the "clear" crystals, this emission is less pronounced. Heat treatment under a cadmium-vapor atmosphere has the effect of decreasing the resistivity by approximately 5 orders of magnitude, while sulphur annealing at 500°C, increases the resistivity of the as-grown crystals by 4 orders of magnitude and creates a new emission peak centered around 620 nm (2 eV). 1. Introduction Cadmium sulphide (CdS) is an important and useful material for optoelectronic applications. The growth of CdS by physical vapor transport (PVT) has been intensively studied for many years [1-3]. A relatively high concentration of defects resulting from the high growth temperature required by previous methods led to a low reproducibility of the results. Recently, a modification of the PVT method was * Corresponding author. Fax: +1 615 329 8634; E-mail: aburger@dubois.fisk.edu. I Present address: Universities Space Research Association, Huntsville, Alabama, USA. reported [4] which produces, at lower growth temper- atures, large crystals having both low dislocation density and second-phase inclusion density. Undoped CdS is always n-type, and the photoluminescent (PL) properties of CdS crystals were extensively studied in the past with respect to its conversion type. Most of the PL properties were studied in the context of intentionally doped crystals [5-7]. Other authors found [8-10] that post-growth heat and illumination treatments affect the general features of their lumi- nescence spectra. CdS, a good model material for the investigation of optical and electronic properties at high pressure, became the focus of several studies [11,12], and renewed interest has been triggered by recent reports on the development of electron-beam- pumped devices [13,14]. 0022-0248/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved

The morphology of freshly cleaved ZnSe surfaces was investigated by atomic force microscopy and the results were correlated with differential scanning calorimetry (DSC) data. Selenium precipitates in undoped ZnSe crystals grown by the physical vapor transport method were determined. The Se inclusions have a size of about 20 nm. A transition temperature at 221°C in the DSC measurement is interpreted as the eutectic temperature of Se-saturated ZnSe. The total amount of the ZnSe Se-rich second phase was 0.8 wt%, and some segregation effect along low angle grain boundaries was evident.

Optical methods have been established for in-ampoule measurements of the iodine vapor concentration during the growth of mercuric iodide (HgI2) single crystals by physical vapor transport (PVT). Significant concentrations of iodine vapor, which can vary during the growth period, occur in some ampoules. The absorptivity of iodine vapor at 514 nm is 7.7 × 105 cm2 mol−1. Differential scanning calorimetry (DSC) measurements correlate with vapor absorption and indicate the presence of free crystalline iodine in vapor-growth HgI2.

In this paper we report an investigation of the morphology of the interfaces of liquid phase epitaxy (LPE) grown HgCdTe thin films on CdTe and CdZnTe substrates by atomic force microscopy (AFM) on freshly cleaved (110) crystallographic planes. An empirical observation which may be linked to lattice mismatch was indicated by an angle between the cleavage steps of the substrate to those of the film. Te precipitates with size ranging from 5 nm to 20 nm were found to be most apparent near the interface.

ZnTe single crystals grown by horizontal physical vapor transport (PVT) and by vertical traveling heater method (THM) from a Te solution were characterized by photoluminescence (PL) at 10.6 K and by atomic force microscopy (AFM). Copper was identified by PL as a major impurity existing in both crystals, forming a substitutional acceptor, Cu Zn . The THM ZnTe crystals were found to contain more Cu impurity than the PVT ZnTe crystals. The formation of Cu Zn -V Te complexes and the effects of annealing, oxygen contamination and intentional Cu doping were also studied. Finally, the surface morphology analyzed by AFM was correlated to the PL results.

Atomic force microscopy (AFM) was used to characterize the surface of lead iodide crystals. The high vapor pressure of lead iodide prohibits the use of traditional high resolution surface study techniques that require high vacuum conditions. AFM was used to image numerous insulating surface in various ambients, with very little sample preparation techniques needed. Freshly cleaved and modified surfaces, including, chemical and vacuum etched, and air aged surfaces, were examined. Both intrinsic and induced defects were imaged with high resolution. The results were compared to a similar AFM study of mercuric iodide surfaces and it was found that, at ambient conditions, lead iodide is significantly more stable than mercuric iodide.

Atomic force microscopy (AFM) is used to examine the structure of freshly cleaved Cd 0.6 Mn 0.4 Te surfaces. The present report complements previous results obtained with X-ray diffraction and optical microscopy which showed the existence of microtwins. The AFM analysis was performed under ambient conditions and yielded nanometer scale resolution images of single twin lamellae that ranged between 20 and 100 nm in width. This is a first observation using AFM of such a substructure, which we interpret as evidence for the presence of nonotwins.

An investigation is being conducted on zone refining α-mercuric iodide. Analytical studies using differential scanning calorimetry and anion chromatography indicate that impurities are accumulated mainly at the end where zone travel terminates. Early results indicate that single crystals can be readily grown from zone-refined material.

CdSe single crystals have been grown from the stoichiometric melt and from Se rich solutions. Here we report the first mid and far infrared spectra of CdSe crystals free of any known impurity bands. Previous studies of the lattice vibrational properties of CdSe crystals have shown the presence of two bands at 538 and 270 cm -1 . Modifications in the purification and crystal growth conditions lead us to assign these two bands to a sulfur impurity. Low temperature photoluminescence spectra are also presented and discussed.

We studied the purification of Se using zone refining, with emphasis on the efficiency of this technique in removing the Cu impurity, which is known to be related to a trapping center in CdSe. After 78 passes it was found that Cu accumulates at one end section of the ingot, while at the opposite end the level was below the detection limit of the atomic absorption spectroscopic analysis employed. Infrared spectroscopic data, differential solubility and differential scanning calorimetry measurements also indicate that the effective distribution coefficient, k, for the Cu solute, is less than 1. A model for the various phases present during zone melting is presented and the possibility of segregating impurities having k>1 is discussed.

We have been able to determine the deviations from stoichiometry of mercuric iodide (HgI 2 ) by using differential scanning calorimetry (DSC). Mercury excess or iodine deficiency in mercuric iodide can be evaluated from the eutectic melting of α-Hgl 2 -Hg 2 I 2 at 235 °C, which appears as an additional peak in DSC thermograms. I 2 excess can be found from the existence of the I 2 -α-HgI 2 eutectic melting at 103°C. An additional DSC peak appears in some samples around 112°C, that could be explained by the presence of iodine inclusions. Using resonance fluorescence spectroscopy (RFS) we have been able to determine the presence of free I 2 that is released by samples during the heating at 120 °C (crystal growth temperature), thus giving additional support to the above DSC results.