ODMR investigations of recombination processes in ZnSe:Cu

New ODMR signals have been observed in ZnSe:Cu crystals by monitoring the Cu-green, Cu-red and the i.r. emissions. The results are interpreted in terms of direct D-A recombination involving Cu_Zn and Cu-X centres and indirect recombination via excited states of these centres.     

Negative crystals of silicon carbide

Systems of negative silicon carbide crystals are classified and studied by experimental methods. The crystal structure and morphology forming during growth, etching, and erosion are discussed.     

Low-temperature luminescence of silicon carbide crystals

The high-energy part of the blue fluorescence of-SiC(6H) is found to be dependent on the nitrogen (donor) concentration. The line fluorescence spectrum is found to include a new series of lines due to radiative transitions to A1 acceptor levels.We are indebted to J.G. Pichugin for providing the crystals.     

Complementary ODMR and photo-ESR studies of deep donor-acceptor pair recombination processes in ZnS and GaP

The complementary approach to studies of deep donor acceptor pair (DAP) recombination processes is presented. On the basis of supplementary light induced Electron Spin Resonance (photo-ESR) and Optically Detected Magnetic Resonance (ODMR) studies, the nature of radiative recombination transitions is cleared out and the centers participating in these transitions are identified. We also show a new approach to determining the recombination rate for DAP’s of different separations. The latter is possible due to frequency-resolved ODMR experiments. The relevant experimental results for deep DAP transitions in ZnS and GaP are presented.     

The character of micropipes in silicon carbide crystals

There has been some question as whether micropipes in SiC crystals, giant dislocations that possess hollow cores and lie roughly along the hexagonal c-direction, are screw dislocations with Burgers vectors of nc, where n is an integer, or are dislocations of mixed character, with Burgers vector nc?+?ma, where m is equal to n or possibly different from n. X-ray topographs of the basal faces of PVT-grown 4H-SiC wafers containing micropipes taken in both back-reflection and grazing-incidence geometries are compared with computer simulations of micropipe images. The deviation from circular symmetry of micropipe images in such topographs may be explained as well by the micropipe's tilt from the c-direction as by an nc?+?ma nature. The contrast of micropipes in electron micrographs comprises of a pair of light and dark lobes consisting of a detailed system of subsidiary fringes. These are comparable with micropipe image computer simulations for Burgers vector nc. When an na edge component is introduced to the simulation, a small feature, a few hundred nm wide, appears, which is absent from the micrographs.     

ODMR study of the nature of iron-red photoluminescence in ZnS crystals

Basing upon the ODMR (optically detected magnetic resonance) measurements on the so-called iron-red (Fe-R) luminescence in ZnS it is shown that the emission is due to the radiative capture of either free or weakly bound electron by substitutional Fe³⁺ associated with an unknown defect residing in n.n. Zn position.     

Erbium in silicon carbide crystals: EPR and high-temperature luminescence

Erbium ions have been incorporated for the first time in bulk 6H-SiC crystals during growth, and they were unambiguously identified from the ¹⁶⁷Er EPR hyperfine structure. High-temperature luminescence of erbium ions at a wavelength of 1.54 μm has been detected. The observed luminescence exhibits an increase in intensity with increasing temperature. The observation of Er luminescence in 6H-SiC offers a promising potential for development of semiconductor light-emitting devices at a wavelength within the fiber-optics transparency window. Fiz. Tverd. Tela (St. Petersburg) 41, 38–40 (January 1999)     

Properties of erbium luminescence in bulk crystals of silicon carbide

The infrared luminescence of Er³⁺ ions has been studied in bulk crystals of silicon carbide 6H-SiC doped with erbium in the process of their growth. The erbium centers of different symmetry in the crystals are revealed by the EPR technique. A number of intense luminescence bands of erbium ions are observed at a wavelength of about 1.54 μm. The luminescence can be excited by the light with quantum energies above and below the band gap of SiC. It is found that the luminescence exhibits unusual temperature behavior: as the temperature increases, the luminescence intensity abruptly rises starting with 77 K, passes through a maximum at ∼240 K, and, in the vicinity of ∼400 K, decreases down to the values observed at 77 K. The activation energies for the flare-up and quenching of the Er³⁺ luminescence are estimated at E _A ≈130 and ≈350 meV, respectively. The mechanisms of the flare-up and quenching of the Er³⁺ luminescence in SiC are discussed. __________ Translated from Fizika Tverdogo Tela, Vol. 42, No. 5, 2000, pp. 809–815. Original Russian Text Copyright ? 2000 by Babunts, Vetrov, Il’in, Mokhov, Romanov, Khramtsov, Baranov.     

Improvement of cubic silicon carbide crystals grown from solution

Cubic-silicon carbide crystals have been grown from carbon-rich silicon solutions using the travelling-zone method. To improve the growth process, we investigated the effect of controlling more tightly some of the growth parameters. Using such improved growth conditions, our best sample is a 12 mm diameter and 3 mm long 3C–SiC crystal. It is grown on a (0001) 2 off, 6H–SiC seed and has 111-orientation. The low amount of silicon inclusions results in a reduced internal stress, which is demonstrated by the consideration of μ-Raman spectra collected at room temperature on a large number of samples.     

掺铜及掺铝多孔硅的光致发光及其发光机理

分别将特定杂质铜和铝引入多孔硅后，观察到了杂质铜和铝所引起的附加发光带：对于没有掺铜的多孔硅，其光致发光谱只有一个发光带；而掺过铜的多孔硅，其光致发光谱出现两个发光带，其中能量较低的发光带随主发光带而变化。在掺铝多孔硅的光致发光谱中，则出现4个与铝杂质能级有关发光带。我们认为上述与杂质有关的发光带是由截流子在杂质深能级上复合所致。     

Kinetics of thermally stimulated recombination processes in lithium borate crystals

This paper reports on the results of the experimental and theoretical investigations of thermally stimulated recombination processes in crystals of the lithium borates Li₂B₄O₇ and LiB₃O₅. For both types of crystals, the measurements of thermally stimulated luminescence curves, spectra, and temperature dependences of the intensities of steady-state X-ray luminescence have been performed in a single experimental cycle. In the framework of a unified model for the Li₂B₄O₇ and LiB₃O₅ crystals, the thermally stimulated recombination processes have been calculated and the obtained results have been interpreted talking into account all available experimental data.     

Characteristics of recombination processes in doped hydrated amorphous silicon films

The results of measurements of the temperature dependences of the dark conductivity and photoconductivity ofa-Si:H films, doped from the gas phase or by implantation of phosphorus or boron ions, as well as the effect of preillumination with white light with different duration on the photoconductivity are presented. A model is proposed for carrier recombination in doped films, taking into account the broadening of the levels of dangling bonds and the difference in the coefficients trapping of electrons and holes on neutral and charged dangling bonds. The dependence of the stationary interband photoconductivity on the equilibrium Fermi level and the appearance of the temperature-induced quenching of the photoconductivity in doped films after preillumination are studied on the basis of this model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 7–17, June, 1987.     

Thermostimulated recombination processes in LiBaF3 crystals

The creation of radiation defects in LiBaF₃ crystals at 10 K and the processes of their thermostimulated recombination are investigated. The methods of optical absorption, thermal bleaching of color centers, thermostimulated luminescence and fractional glow technique are used. The radiation defects anneal in a multi-stage process accompanied with thermo-luminescence at 20, 46, 105, 130, 170, 210 and 270 K. Differences in the optical absorption spectra measured before and after the TSL peaks are obtained and recombination parameters are determined. The TSL peak at 20 K arises from the delocalization of H-centers. The presence of two TSL peaks related to V_K-centers at 105 and 130 K indicates that 60° and 90° migration hops occur.     

Ground state properties of the group IV ionic compound silicon carbide

The basic ground state properties of cubic silicon carbide are calculated fully ab initio using the Local Density Functional method and norm-conserving pseudopotentials, with atomic numbers and the crystal structure as the only inputs. The distribution of the valence charge density suggests that the bonding in SiC is essentially ionic.     

Growth of negative filamentary crystals during spark cutting of silicon carbide

Experiments are described which show that under pulsed thermal loading conditions, a damaged layer is formed in SiC which inherits the typical erosion defects (craters, chips, microcracks). Zh. Tekh. Fiz. 68, 133–135 (July 1998)     

Ab initio study of palladium and silicon carbide

Ab initio methods have been used to investigate the properties of Pd as impurity in bulk SiC at five charged states within the framework of density functional theory using the local spin density approximation. It was found that Pd interstitials and substitutionals have similar energy to their intrinsic counterparts. In addition, Pd substitutes for a vacancy, di-vacancy, and tri-vacancy with similar energies. Pd diffuses through SiC via an interstitial mechanism employing the tetrahedral sites and Pd can substitute for Si and C at positive charged states. Removing electrons (p-type doping) from SiC lowers the formation and migration energies of Pd defects in SiC for most configurations.     

Thermostimulated surface segregation processes in ionic crystals: Potassium chloride

The chemical and phase composition, and cleavage surface morphology and the vapor composition of potassium chloride (KCl) crystals formed as a result of the thermostimulated surface autosegregation (TSAS) are studied by methods of microprobe analysis, high-resolution scanning electron microscopy, optical digital microscopy, and quadrupole mass spectrometry. It is experimentally found that the stoichiometry (K/Cl <1) in the surface layers changes due to a decrease in the potassium surface concentration from 5% in the initial samples to 12% after annealing at a temperature of 1023 K. After annealing at a temperature of 573 K for 5 h at P = 10^?3 Pa, the potassium deficiency increases to 17%. The competing processes resulting in TSAS in potassium chloride are the self-diffusion of potassium to the surface and its subsequent sublimation. During the annealing processes the sublimation of potassium dominates, but at a temperature near fusion, the self-diffusion of potassium to the surface increases. It is concluded that potassium chloride analogous to sodium chloride is a rather stable compound to TSAS. This is an additional argument of the important role of ionic bonds in a decrease in the tendency of chemical compounds to surface autosegregation.     

On the recombination of intrinsic point defects in dislocation-free silicon single crystals

The recombination of intrinsic point defects in dislocation-free silicon single crystals is investigated. It is established experimentally and confirmed by thermodynamic calculations that this process in the vicinity of the crystallization front is hindered by the recombination barrier. The recombination parameters (such as the recombination barrier height, the recombination time, and the recombination factor) for the model describing the dynamics of point defects at low and high temperatures are evaluated in terms of the heterogeneous mechanism of nucleation and transformation of grown-in microdefects. It is confirmed that the decomposition of a supersaturated solid solution of point defects can occur according to two mechanisms, namely, the vacancy and interstitial mechanisms. Vacancies and intrinsic interstitial silicon atoms find sinks in the form of oxygen and carbon background impurities. It is demonstrated that the formation of “intrinsic-point-defect-impurity” pairs is a dominant process in the vicinity of the melting temperature.