Features of the dark conductivity of zinc selenide

The experimentally obtained I–V dependences of the dark conductivity of zinc-selenide single crystals have a nonlinear character. The contact phenomena, injection currents, and the Poole-Frenkel effect are considered among the possible causes of such behavior of the I–V characteristics. As a result of investigation, the following is established: (i) the contact between the n-ZnSe single crystal and metallic In is ohmic; (ii) in low fields, the I–V characteristic obeys Ohm’s law; (iii) in strong fields, the dark conductivity of the investigated samples is determined by the Poole-Frenkel effect. Also Poole-Frenkel theory is supplemented for different potentials of interaction of the local center with the charge carrier.     

Optical properties of polycrystalline zinc selenide

Dependences of the exponent of radiation flux attenuation on the ZnSe grain size and the wave-length are experimentally determined. At a wavelength of 1.1 μm, the minimum and maximum attenuation is observed in crystals with the smallest and largest grain sizes, respectively. A reverse situation arises at a wave-length of 10 μm. It is concluded that the optical radiation at wavelengths of 1.1 and 10 μm is scattered at internal grain defects and mainly at grain boundaries, respectively. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 3, 2004, pp. 322–324. Original Russian Text Copyright ? 2004 by Bryzgalov, Musatov, Buz’ko.     

Photoluminescence of nitrogen-doped zinc selenide epilayers

Photoluminescence (PL) studies of nitrogen doped ZnSe epilayers grown by molecular beam epitaxy have been performed as a function of excitation wavelength, power density, and temperature. The broad emission from heavily doped ZnSe:N is composed of two distinct bands which we label as N_I and N_II. The dominant band N_I appears at 2.54 eV, while the N_II band position is sensitive to excitation power and occurs between 2.55 and 2.61 eV. The N_I emission energy is insensitive to incident power or temperature over the ranges studied. Further, a 69 meV localized phonon of the N_I band is observed. We propose that the N_I band is related to transitions within a (V_se+-Zn-N_se-)0 close-associate pair. The N_II band displays characteristics consistent with the conventional donor acceptor pair model. A third band N_III at 2.65 eV is observed under high-power pulsed excitation. Previous studies of heavily doped ZnSe:N had suggested that the broad emission band was described by a modified donor-acceptor pair model. Our PL study does not support this previous model. In addition, our data suggests that singly ionized selenium vacancy complexes form in heavily doped ZnSe:N and play a role in compensation.     

硒化锌晶体的高效率高质量组合抛光方法（特邀）

硒化锌晶体作为常用的红外晶体材料,广泛应用于红外光学系统中。为了提高硒化锌晶体的加工质量及加工效率,提出了将磁流变抛光（MRF）与传统数控抛光(CCOS)技术相结合的方法,通过多组正交实验配置硒化锌晶体的磁流变抛光液,对一块口径为50 mm的硒化锌晶体展开磁流变抛光,再针对磁流变抛光后的表面痕迹进行传统数控抛光,在正压力为0.05~0.1 MPa范围内,经过30 min均匀抛光,硒化锌晶体的表面粗糙度由3.832 nm降低到1.57 nm,粗糙度得到明显改善。该方法有效提高了非球面硒化锌晶体的加工效率并改善了加工后的表面质量,对硒化锌晶体的非球面超精密加工具有重要的参考价值。     

Effect of impurities on the color of polycrystalline zinc selenide

The results of studies of polycrystalline zinc-selenide samples different in color are reported. It is established that the impurity absorption band corresponding to (ionized acceptor)-(conduction band) transitions defines the color of the material.     

Brush electrodeposited silver indium selenide films and their optical characteristics

Silver indium selenide films were brush electrodeposited on tin oxide coated glass substrates at different substrate temperatures. The films were single phase with chalcopyrite structure. Optical absorption measurements indicated a band gap in the range of 1.20–1.30 eV with decrease of substrate temperature. Transmission spectra exhibited interference fringes. Using the envelope method, calculated values of refractive index at 850 nm decreased from 3.53 to 2.62 with decrease of substrate temperature. From the refractive index data, the value of N/m^⁎ was estimated to be in the range of 0.89–1.22. Optical data were analyzed by the single-effective oscillator model, and the single oscillator energy as well as the dispersion energy was estimated. The single oscillator energy decreased from 1.83 eV to 1.68 eV with the increase of substrate temperature. The dispersion energy increased from 5.42 eV to 12.25 eV with the increase of substrate temperature.     

Nonadditive photoconductivity and induced states in zinc selenide crystals

The distribution of growth defects of various types arising in zinc selenide crystals grown from the melt under highly nonequilibrium conditions determines different, but interrelated metastable states of samples cut from different parts of the same ingot. The characteristic features of the dielectric response of these states, as well as of the states induced by an external action, are established.     

Determination of the ionization energy of vanadium levels in zinc selenide

By comparing the experimental spectra of optical absorption and photoconductivity with those calculated using the Lucovsky formulas, it is established that the V impurity in ZnSe forms acceptor levels with the ionization energy 0.62 eV.     

Surface states in electroluminescent MIS diodes of zinc selenide

Measurements of the shunt conductance of electroluminescent MIS diodes of zinc selenide show that the density of surface states in a device in which the metal (gold) electrode was deposited on an etched surface, was of the order of 4 × 10¹¹ cm^?2 eV^?1. When the gold was evaporated on to cleaved surfaces the surface state density was reduced to about 5 × 10¹⁰ cm^?2 eV^?1. The low density of surface states means that donor densities calculated in the normal way from standard C–V measurements are only 6% too high if the measurements are made at 100 kHz and 2% too high if 200 kHz is used.     

Mechanisms of current flow in zinc telluride-zinc selenide heterojunctions

The electrical properties of zinc telluride-zinc selenide heterojunctions prepared by solid-phase substitution reactions are investigated. It is established that the forward current is governed by tunneling-recombination processes at low biases and by above-barrier carrier diffusion at high biases. The initial segments of the reverse branches of the I-V characteristics are described on the basis of the model of tunneling carrier transmission with the participation of deep levels. For high reverse biases the current was found to increase abruptly as a result of impact ionization. Fiz. Tekh. Poluprovodn. 31, 1074–1076 (September 1997)     

Utilization of optical and electrical peculiarities of partially compensated zinc selenide

Zinc selenide bulk crystals are doped with group III and group VII impurities (aluminum and iodine). Compensating A-center concentrations are controlled using a partial pressure equilibration technique. This facilitates a more flexible ‘adjustment’ of electrical transport properties and optical characteristics, which recently attracted attention for device application. Furthermore, advanced methods of point defect characterization can be applied.     

Effect of vacuum annealing on the edge luminescence of undoped zinc selenide

It has been established experimentally that vacuum annealing of undoped ZnSe crystals in the temperature range 700–1200 K leads to a significant increase in the intensity of the blue luminescence band and suppression of the red-orange band. A model for defect formation is proposed to explain the observed characteristics.     

Nonlinear optical transmission induced by large transient electricfield enhancements in photoconductive zinc selenide switches

We report our investigation on photoconductive power switching using polycrystalline zinc selenide with transparent liquid electrolytic electrodes. Nonlinear optical transmission which is due to high internal electric fields of this switch under moderate biases was observed. From the optical transmission measurements, large and fast electric field variations inside the switch were deduced. Electric field compression inside the switch, which can be attributed to the switch geometry and the electro-absorption effect, was responsible for the observed large optical absorption. Our model provided explanations for these observations     

Nature of the blue emission band in zinc selenide containing sulfur isovalent impurity

The edge luminescence of ZnSe heterolayers on ZnSe substrates obtained by isovalent substitution is investigated. It is shown that the blue emission line originates from band-to-band recombination and the annihilation of excitons upon their inelastic scattering at free charge carriers.     

Specific features of the luminescence and conductivity of zinc selenide on exposure to X-ray and optical excitation

The set of experimental data on the X-ray-excited luminescence and X-ray induced conductivity of ZnSe are compared to the data on the photoluminescence and photoconductivity. It is experimentally established that the current-voltage characteristics and the kinetics of phosphorescence and current relaxation depend on the type of excitation. It is found that the external electric field influences the intensity and shape of bands in the luminescence spectra. It is shown that the character of excitation defines the kinetics of recombination, charge carrier trapping, and conductivity in wide-gap semiconductors.     

Fabrication of waveguide tapers by semitransparent mask photolithography

An improved process for semitransparent mask lithography is described. The uniformity of mask transmittance is increased by adapting the electron beam exposure field size to a binary multiple of the pattern period. In addition surface roughness of resist patterns is reduced by exposure of the resist-coated sample to an acetone atmosphere which results in negligible micro roughness.

Using this process waveguide tapers employing a symmetric layer structure were fabricated. The tapers exhibit fiber-chip coupling losses of 1.6 dB after Fresnel correction and lateral alignment tolerances of ±2.2 μm for 1 dB excess loss. These values are comparable to results obtained for waveguide tapers fabricated using direct write electron beam lithography. This proves the described process to be suitable for the fabrication of relief type structures for optoelectronic integrated circuits.     

The structure of high-temperature blue luminescence centers in zinc selenide and mechanisms of this luminescence

The characteristic features of temperature quenching of the intensity of the edge luminescence bands of n-ZnSe crystals annealed in different media (vacuum, Zn, Se) are investigated a wide temperature range. A change in the mechanisms of high-temperature exciton luminescence in the short-wavelength region of the spectrum (443 nm) with increase in temperature of the crystal is observed. It is shown that the nature of temperature quenching of the long-wavelength edge luminescence band (458 nm) is evidence of dissociation of associative luminescence centers with increase in the sample temperature. Fiz. Tekh. Poluprovodn. 32, 178–181 (February 1998)     

Development of silver zinc oxide for general-purpose relays

The switching behavior of silver cadmium oxide (Ag/CdO), silver tin oxide (Ag/SnO/sub 2/) and silver iron oxide (Ag/Fe/sub 2/O/sub 3/) contact materials is compared to silver zinc oxide (Ag/ZnO) materials having different amounts of additives. Endurance tests were performed in a commercial general-purpose relay, subjected to resistive, inductive and inrush current loads. Results showed the performance of Ag/ZnO to be significantly dependent on the amount of additives and their grain size. The optimum Ag/ZnO was found to be equivalent or superior to other silver metal oxides depending on the applied load. Thus a substitution of Ag/CdO by an environmentally harmless Ag/ZnO material is possible.