Investigation of radiation defects in electron irradiated Hg1−xCdxTe crystals using positron annihilation

The electron characteristics of defects in the initial and electron irradiated Hg_1−xCd_xTe (2–3 MeV, 10¹⁸ cm⁻², 300 K) crystals using the positron annihilation method have been investigated. The data of electric measurements are confirmed on connection of p-type conductivity with vacancy defects of metal sublattice initial crystals Hg_1−xCd_xTe. An analysis of correlation curves of irradiated crystals has shown a possibility of formation of associations of initial defects and radiation damages of vacancy type during radiation process. The presence of narrow component on correlation curves in the region of small angles is associated with formation of positronium states localized in the region of radiation defect complex of vacancy type. Identification of positron-sensitive defects with electrically active radiation induced ones has been carried out according to the results of isochronal annealing of irradiated crystals.     

Photoelectric properties of magnetically sensitive MOS structures

The photoelectric properties of MOS structures having compensation regions near the field electrode have been studied experimentally. It is shown that the presence of such regions can lead to the appearance of a number of features in the integrated photoelectric properties: the presence of a large photovoltage signal in enhancement, dependence of the form of the photovoltage frequency dependence on the intensity of the light flux, and distortion of the shape of the photovoltage signal in inversion. The presence of compensation regions can be established using measurements of the distribution of the photovoltage over the area of the structure and measurements of the voltage dependence of the phase of the integrated photovoltage signal. The increase or decrease of the photovoltage signal in enhancement after exposure to a weak magnetic field is due to the rearrangement of the impurity-defect structure in the near-surface layer of the semiconductor, leading to the appearance of compensated semiconductor regions near the field electrode. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 82–87, May, 1998.     

Special Features of Local Photoelectrical Properties of Inhomogeneous Metal–Insulator–Semiconductor Structures

Local photoelectrical measurements are used to study anomalous electrical properties of metal–insulator–semiconductor structures (decrease in photoemf in inversion). The inhomogeneous surface potential in the gap between the regions beneath and behind the electrode and between different parts of the region beneath the electrode may lead to a decrease in the local photoemf in inversion.     

Intercomparison of radiation measurements on STS-63

A joint NASA Russia study of the radiation environment inside the Space Shuttle was performed on STS-63. This was the second flight under the Shuttle-Mir Science Program (Phase 1). The Shuttle was launched on 2 February 1995, in a 51.65° inclination orbit and landed at Kennedy Space Center on 11 February 1995, for a total flight duration of 8.27 days. The Shuttle carried a complement of both passive and active detectors distributed throughout the Shuttle volume. The crew exposure varied from 1962 to 2790 μGy with an average of 2265.8 μGy or 273.98 μGy/day. Crew exposures varied by a factor of 1.4, which is higher than usual for STS mission. The flight altitude varied from 314 to 395 km and provided a unique opportunity to obtain dose variation with altitude. Measurements of the average east-west dose variation were made using two active solid state detectors. The dose rate in the Spacehab locker, measured using a tissue equivalent proportional counter (TEPC), was 413.3 μGy/day, consistent with measurements made using thermoluminescent detectors (TLDs) in the same locker. The average quality factor was 2.33, and although it was higher than model calculations, it was consistent with values derived from high temperature peaks in TLDs. The dose rate due to galactic cosmic radiation was 110.6 μGy/day and agreed with model calculations. The dose rate from trapped particles was 302.7 μGy/day, nearly a factor of 2 lower than the prediction of the AP8 model. The neutrons in the intermediate energy range of 1–20 MeV contributed 13 μGy/day and 156 μSv/day, respectively. Analysis of data from the charged particle spectrometer has not yet been completed.     

A study of the radiation environment on board the Space Shuttle flight STS-57

A joint NASA-Russian study of the radiation environment inside a SPACEHAB 2 locker on Space Shuttle flight STS-57 was conducted. The Shuttle flew in a nearly circular orbit of 28.5 degrees inclination and 462 km altitude. The locker carried a charged particle spectrometer, a tissue equivalent proportional counter (TEPC), and two area passive detectors consisting of combined NASA plastic nuclear track detectors (PNTDs) and thermoluminescent detectors (TLDs), and Russian nuclear emulsions, PNTDs and TLDs. All the detector systems were shielded by the same Shuttle mass distribution. This makes possible a direct comparison of the various dose measurement techniques. In addition, measurements of the neutron energy spectrum were made using the proton recoil technique. The results show good agreement between the integral LET spectrum of the combined galactic and trapped particles using the tissue equivalent proportional counter and track detectors between about 15 keV/micrometers and 200 keV/micrometers. The LET spectrum determined from nuclear emulsions was systematically lower by about 50%, possibly due to emulsion fading. The results show that the TEPC measured an absorbed dose 20% higher than the TLDs, due primarily to an increased TEPC response to neutrons and a low sensitivity of TLDs to high LET particles under normal processing techniques. There is a significant flux of high energy neutrons that is currently not taken into consideration in dose equivalent calculations. The results of the analysis of the spectrometer data will be reported separately.     

Investigation of photoelectric and recombination characteristics of a CdHgTe optical mixer

An analysis is made of the heterodyne operation of a Cd_xHg_1–xTe (x=0.2) photoresistor detector. An allowance is made for the influence of the heterodyne power on the carrier lifetime in the case of the interband Auger recombination and recombination via Shockley-Read centers. It is found that the Auger recombination predominates at high heterodyne powers. It is shown that the pass band of the photodetector can be widened by increasing the heterodyne power. It is reported that the results of an experimental study of a Cd_xHg_1–x Te photoresistor detector are in good agreement with the calculations when the threshold sensitivity of the detector is limited by the thermal noise of the photoresistor.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 100–103, July, 1980.     

High temperature defects in electron irradiated semiconductors HgCdTe,PbSnTe

The peculiarities of defect formation in n- and p-type conductivity HgCdTe and PbSnTe crystals after electron irradiation (2 MeV, 300 K) up to 2 × 10¹⁸ cm^-2 are examined. It has been found that irradiation results in formation of n-type conductivity crystals with final parameters that are determined by the composition of initial samples. The annealing of radiation defects occurs in the 360–470 K temperature range. It has been believed that the change of HgCdTe, PbSnTe properties after electron irradiation at 300 K are connected with formation of radiation defects, including Te vacancies.     

Radiation defects in Ar+-ion-implanted Hg1−xCdxTe crystals

A study has been made of defect formation in Hg_1–xCd_xTe crystals after implantation with argon ions possessing energies of 50 and 150 keV over a wide range of radiation doses. The spatial distributions of electrically active radiation defects, measured by electrophysical methods, are compared with extended lattice imperfections, determined from Rutherford backscattering spectra. The distribution of radiation donors has been found to be shifted deeper into the semiconductor beyond the region of the interstitial impurity distribution and radiation donors have been found to be neutralized by extended lattice imperfections. The paper discusses the principal factors in the formation of the profiles of the carrier concentration distribution in the implanted cadmium telluride-mercury layer.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 83–90, December, 1988.