V. V. Serdyuk

ZnSe blue-light-emitting diode

Abstract A zinc selenide p-n junction diode has been formed by Li thermal diffusion. Blue electroluminescence has been observed from this structure in forward bias at room temperature. The external quantum efficiency is about 0.5%.

Influence of technological conditions upon the luminescence properties of ZnTe-ZnSe heterostructures grown by liquid-phase epitaxy

This paper studies the luminescence characteristics of the components of ZnTe-ZnSe hetero-structures obtained by liquid-phase epitaxy of ZnTe and SnSe substrates oriented in the (III) plane; the epitaxy was based on a solution-melt in metal (Sn, Bi). The influence of the metal melt and the technological conditions of crystal growing upon the luminescence properties of the ZnSe substrate is studied. The authors followed the changes in the ZnSe luminescence spectrum in each stage of the study. Typical photoluminescence spectra is shown of ZnSe single crystals which had been grown recently and annealed in liquid Zn. When ZnTe-ZnSe heterostructures are produced by liquid phase epitaxy from solution melts in Bi and Sn, the radiative properties of ZnSe substrates do not change because disturbances of stoichiometry are prevented. The luminescence properties of ZnSe substrates which were subjected to annealing can be described by the concepts of annealing ZnSe with copper.

The influence of annealing in liquid zinc on the photoluminescence spectrum of single crystals of ZnSe

In most cases, single crystals of zinc selenide grown without the deliberate introduction of impurities either do not exhibit luminescence at all or show extremely weak luminescence. In order to increase the brightness of the luminescence, ZnSe crystals are annealed in liquid zinc [1]. It is known that this is accompanied by the extraction of Cu, Fe, and other heavy metal impurities from the material of the semiconductor [2]. In addition, the formation of zinc vacancies leads to an increase in the intensity of serfactivated luminescence [1, 3]. At the present time it is possible to find contradictory information on the localization of the serfactivated luminescence bands of zinc selenide. Some authors consider that the serf-activated luminescence band of ZnSe lies in the range 640-650 am [4, 5]. Other workers [3, 6, 7] assign the band with ~max = 600610 am to the serf-activated luminescence. It may be noted that the emission of ZnSe due to copper impurity is also localized in the orange-red range of the spectrum [3, 8], so that the problem of differentiating the self-activated and impurity luminescence in this range of the spectrum remains. We studied single crystals of zinc selenide grown from the melt. In the original state, the specimens did not exhibit appreciable luminescence in the visible range of the spectrum, and showed only an infrared band with a maximum at ~ = 950 nm (curve i in Fig. 1). The crystals were annealed in quartz ampuls evacuated to a pressure of 10 -5 mm Hg and containing a certain quantity of highly pure zinc. When the appropriate temperature was reached, the zinc melted, and the crystals were immersed in the resulting molten metal. The crystals were heated at a melt temperature of 900~ The duration of the treatment could be varied from 1 h to several tens of hours. The measurement of the luminescence spectra of the crystals subjected to annealing in molten zinc made it possible to divide them into two groups, The specimens of the first group (after annealing for a period of 48 h) showed three luminescence bands at a temperature of 103~ with maxima localized in the region of 550, 640, and 950 am (curve 2 in Fig. 1). The specimens of the second group, obtained after annealing for a period of 72 h at the same temperature, were characterized by a single luminescence band localized in the region of 610 am. Subsequently, we paid particular attention to the characteristics of the luminescence band in the orange (~max = 610 nm) and red (Xmax = 640 urn) regions of the spectrum. It was found that the excitation spectra of these bands are different. The radiation with ~max = 610 nm is excited only by light from the region of the characteristic absorption of ZnSe, whereas the band with Xmax = 640 nm is also observed with excitation of the crystal with light from the region of the impurity absorption. It was also shown that the temperature dependence of the intensity of the luminescence in each of these bands, plotted on coordinates In [(I0/D -1] vs l/T, is characterized by two activation energies (Fig. 2).

Superlinearity of light-current characteristics of cds films grown in an oxygen-containing atmosphere

A study is made of features of the light-current characteristics (LCC) of thin cadmium sulfide films obtained by deposition of an aerosol of the reagent solution on a heated substrate. Nonlinearity of the film LCC and photosensitivity can be effectively controlled by thermooptical processing (specimen annealing in an air atmosphere in the presence of illumination). It is established that superlinearity of the specimen LCC is caused by an increase in charge carrier mobility with increase in the intensity of photo-excitation. A relatively weak change in nonequilibrium electron lifetime with a significant increase in their mobility leads to the conclusion that in such films the recombination centers which essentially determine carrier lifetime are located outside the region of intercrystallite barriers. The calculated LCC is slightly superlinear and is found to be in good agreement with experimental characteristics obtained for specimens grown or thermoprocessed in the absence of illumination.

Photoconductivity instability in thin polycrystalline CdS layers with high surface-charge density

The instability of the photocurrent in thin CDS films prepared by the electrohydrodynamic sputtering method is investigated. The degradation of photosensitivity of the films during prolonged illumination and the restoration of their photosensitivity in dark are explained by assuming the drift of ionized lattice defects in the field set up by negatively charged oxygen adsorbed on the surface of the crystallites. The spatial distribution of the potential in a crystallite is calculated, demonstrating a substantial change in the height and profile of the intercrystallite barriers as a result of the drift of defects.

Stimulation of an anomalous temperature dependence of dark current in polycrystalline cadmium sulfide layers

i. V.I. Nefedov, E. K. Zhumadilov, and T. Yu. Kopytova, Zh. Struct. Khim., 18, 692 (1977). 2. M.K. Bahl and R. O. Woodall, J. Chem. Phys., 64, 1210 (1976). 3. L. Asplund, P. Kelfve, et al., Chem. Phys. Lett., 40, 353 (1976). 4. S.P. Kowaiezyk and R. A. Pollak, Phys. Rev. B, 8, 2387 (1973). 5. C.D. Wagner, Anal. Chem., 47, 1201 (1975). 6. A.N. Pavlov, R. V. Vedrinskii, and V. V. Krivitskii, Izv. Vyssh. Uchebn. Zaved., Fiz., No. 3, 106 (1978). 7. D. Goschinski, G. Howat, and T. Xberg, J. Phys. B, 8, ii (1975).

Effects due to field displacement of charged vacancies in the crystal lattice of cadmium sulfide

In single crystals of CdS with indium electrodes an asymmetry in the volt-ampere characteristic has been discovered which develops after the passage of large currents at elevated temperatures. A change in the resistivity of the specimen in a direction from the cathode to the anode is simultaneously observed, associated with the high-temperature drift of charged vacancies.

Phenomena caused by the capture of carriers injected into illuminated cadmium selenide single crystals

The current-voltage characteristics of the dark current and the photocurrent excited by light from the edge region of the fundamental absorption have been measured for CdSe single crystals fitted with sandwichtype indium-gallium electrodes and guard rings to eliminate surface currents. At a certain voltage, the photocurrent characteristics show a tendency toward saturation, due to the filling of traps by charge carriers injected from the cathode, which causes a reduction of the conduction-electron mobility.

Dynamic behavior of indium contacts with single crystals of cadmium sulfide above room temperature

Dark-current relaxation is observed with single crystals of cadmium sulfide after voltage has been applied. The kinetics of this reaction have been measured with respect to voltage and temperature. The observations are explained from the viewpoint of filling and emptying of electron traps in the contact regions of the crystals.