In this paper we present results of our investigations on the technology improvement for high-grade CdTe<Cl> and CdZnTe single-crystals growth as well as results of the obtained materials testing by photoluminescence method. Perspectives for the materials utilization in detectors and devices of radiation control are discussed. Design features and characteristics of the developed personal (gamma) - and X-radiation dosimeters on the base of CdTe<Cl> detectors and (gamma) -radiation spectrometers on the base of CdZnTe detectors are presented and discussed as well.
Photoluminescence properties of short-period asymmetric GaAs/AlAs superlattices with the well and barrier thickness varied from 10 to 3 monolayers were studied at high optical excitation. It was shown that an asymmetric structure of the superlattice, in which the well layers are at least twice wider than the barrier ones, allows us to maintain the direct band gap and, hence, to improve emission properties for any well width. This is important for utilization of such structures in light-emitting devices. The stimulated emission at 80 K was observed for a GaAs/AsAs superlattice with the well and barrier thickness of 6 and 3 monolayers, respectively. At the same time, investigations of the dependences of the emission intensity on the pump intensity for different superlattices revealed an enhancement of nonradiative recombination with decreasing the well thickness due to an enhanced influence of interface roughness.
Etching with bromine in methanol of the CdTe single crystals (as-grown and purified by extraction treatments) was performed on the (110) and (111)A surfaces. The crystals have been studied by Auger electron spectroscopy and low temperature photoluminescence. A correlation between results of Auger electron spectroscopy and features of photoluminescence spectra has been found. On the basis model which considers that etching related Cl acts as a non-(Gamma) associated defect the `hot' photoluminescence beyond the fundamental absorption edge of CdTe has been explained.
The effectiveness of radiative recombination of GaP light- diode structures, grown by means of epitaxial technique, is determined by deep nonradiative level concentration, which can be changed by irradiation of samples with fast particles or with the help of ultrasonic treatment. Variations of the nuclear particle doses and energies as well as ultrasonic waves allows to find optimal regimes for treatment of crystals, when the influence becomes positive, i.e., an increase in the light-diode quantum yield is observed. In the crystals treated by ultrasonic at low temperatures (77 degree(s) K) a luminescence intensity was found which are synchronous with those of current. The oscillations mentioned are likely to be caused by formation of mobile dislocation domains involved in the creation of dark lines and defects of dark spots. The work emphasizes a crucial role of dislocation networks in the formation of the fields of nonradiative recombination in an ultrasonic-treated sample bulk.
Temporal characteristics of the carriers recombination were investigated in different types of GaAs/AlAs superlattices by the time-resolved photoluminescence spectroscopy. The peculiarities of the electron-hole transitions were established for the superlattices studied in the dependence of the superlattice type and the width of quantum well and barrier layers. In particular, the conditions of existence of free and localized on the interface roughness excitons were found.
Unique polarization properties of the exciton luminescence in semiconductor superlattices (SL) are the subject of a great current interest. Polarization effects in SLs may be caused by different mechanisms, such as formation of twodimensional subbands, exciton localization, existence ofthe microreliefat heterointerfaces, etc. [1-3]. We have investigated the polarization properties ofthe photoluxriinescence (PL) spectra of GaAs-AlAs superlatlices in a wide range ofquantum well and barrier widths. The sample parameters, i.e. well width d, the barrier width d, the number ofperiods N, the type of SL, and the corresponding degrees oflinear polarization are listed in table 1. In both direct-gap SLs-I (d <4 n.tn) and indirect-gap SLs-II (d <4 nm) the polarization of PL lines is caused by the splitting of heavy and light hole bands and the anisotropy ofheavy holes, but this effect alone cannot explain the polarization ofthe luminescence irradiated in the direction normal to the surface of investigated structure (i.e. at small detection angles). For SLs-I we have observed rather large linear polarization PL=(I-I)/(I.,+IS), where I and I are the intensifies of exciton luminescence polarized in the plane ofdetection and normal to it. In this case polanzation may achieve values ofabout 20%. In SLs-II with narrow wells photoluminescence is caused by indirect exciton transitions between X-electrons of AlAs and r -heavy holes of GaAs. It is known that such excitons are localized at interface inhomogeneities [4]. The value of P1 for these SLs is lower than for the SLs-I (L=5-1° %). We have studied the dependence ofpolarization degree on the angle of PL detection for SL—II with the well width 3.4 run and barrier width 4.0 nm for two cases of crystallographic directions ([1 10] and [1 1 0]). The parameters of such samples were close to the case when direct —indirect crossover is observed. As a consequence of this fact two lines were observed in PL spectrum, one of which is associated with indirect recombination of X-electrons and another with direct recombination of F-electrons. r-Iine is almost unpolarized (L'1)' while X-line is characterized by rather large polarization degree (up to 10%), which decreases with the increase ofdetection angle and changes its sign (for small detection angles) with the 90°-turn of the sample around the axis normal to its surface. This anomalous behavior requires an adequate theoretical explanation. From our point ofview such explanation may be given if the existence of heterointerface corrugations in superlattice is taken into account. At the same time the fact ofsmall broadening of observed PL line (substantially lower than possible line splitting due to monolayer fluctuations in quantum well width) proves a strong correlation between such corrugations on both sides ofeach quantum well, i.e. the shape of corrugations in heterointerfaces in superlattice is determined by the shape of corrugations on the surface ofthe substrate.
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