E. M. Gavrishchuk

A study of luminescence centers related to copper and oxygen in ZnSe

The effects of deviation from stoichiometry and the copper and oxygen concentrations on cathodoluminescence spectra were studied in ZnSe condensates obtained by chemical vapor deposition and doped with Cu during growth. The results were supplemented with the study of the microstructure and microcomposition using scanning electron microscopy, measurements of electrical conductivity, and calculations of the equilibrium between the native point defects. It is shown that three types of Cu-related centers are always accompanied with self-activated centers that include oxygen at the Se lattice site (OSe). The paired centers SA(I)-Cu(I), SAL(II)-Cu(II), and III-Cu(III) are typical of all II-VI compounds. All observed I-III Cu-containing centers are associative. Models of emission centers are suggested. A change of the emission type I-III is related to the recharging of the same group of defects that include OSe, Zn(Cu), and VZn. New phenomena that occurred in the region of I-III bands and were related to the profound purification of the material were observed.

Specific features of luminescence spectra of ZnS:O and ZnS:Cu(O) crystals in the context of the band anticrossing theory

The anticrossing band theory, which specifies the change induced in the band structure by an isoelectronic impurity substantially distorting the lattice, is used to interpret the nature and specific features of the complex self-activated luminescence spectra of ZnS:O and ZnS:Cu(O). The light emission involving the self-activated luminescence centers SA and SAL, the spectral dependence of the emission components in relation to the content of dissolved oxygen, and the effects of the centers on the formation of bound excitons are considered. It is found that some absorption bands in the near-infrared spectral region are associated with the transitions between sublevels of the conduction band split in the presence of oxygen. On the basis of the experimental data, a heretofore unknown band model of ZnS:O is developed, and the Cu-induced modifications of the model are discussed. The effect of oxygen-containing agglomerates on the spectra is established. It is suggested that these agglomerates can be responsible for green emission from ZnS:Cu. The results complement the previously reported data of similar studies of ZnS:O and ZnS:Cu(O).

Effect of Hot Isostatic Pressing on the Elastic and Optical Properties of Polycrystalline CVD ZnS

Hot isostatic pressing (HIP) is shown to increase the Youngs modulus and transmittance of polycrystalline zinc sulfide produced by chemical vapor deposition. Both effects are associated with the decrease in the relative volume of nonequilibrium crystallite boundaries containing dangling bonds, which are responsible for the formation of bound surface charges, leading to interfacial polarization. The secondary recrystallization induced by HIP leads to the formation of thin, equilibrium grain boundaries.

Self-propagating high-temperature synthesis of Y2O3 powders from Y(NO3)3x(CH3COO)3(1 − x) · nH2O

We have studied the self-propagating high-temperature synthesis (SHS) of yttrium oxide from Y(NO3)3x(CH3COO)3(1 − x) · nH2O (0.3 ≤ x ≤ 0.7) acetate nitrates, calculated their standard enthalpies of formation using the method of valence states of atoms in a chemical compound, and compared calculated and experimentally determined yttrium oxide SHS temperatures. Using thermogravimetry and differential scanning calorimetry data and thermodynamic analysis, we have determined the optimal range of yttrium acetate nitrate compositions for the SHS of Y2O3 powder.

Recrystallization Behavior of ZnS during Hot Isostatic Pressing

The effect of hot isostatic pressing conditions on the microstructure of CVD ZnS has been studied. The results have been used to analyze the mechanisms of zinc sulfide recrystallization at high temperatures and pressures.

Effect of oxygen doping on the IR transmission and cathodoluminescence of ZnSe

The effect of oxygen doping (0.9 and 4.3 vol % O2in the gas phase) on the transmission and cathodoluminescence of CVD ZnSe was studied. The incorporation of oxygen was found to reduce the transmission in the spectral range 700–1900 cm–1. Examination by scanning electron microscopy shows that Se excesses and high O2concentrations lead to tabular growth. ZnO precipitation at structural defects during cooling was observed only in the end portion of the deposit. The dimensions of microinhomogeneities are shown to have a significant effect on the transmission of ZnSe. The oxygen-containing species present in the deposits were identified using cathodoluminescence spectra. The CL spectrum of Se-enriched p-type ZnSe is dominated by the band at 490 nm (SAL) at 80 K and the band at 640 nm (SA) at 300 K. The 640-nm band is attributed to recharging of the SALcenters upon a variation of the Fermi energy with temperature. Decreasing the Se excess leads to the quenching of the SALemission and appearance of the shorter wavelength component of the SAband at 600 nm (80–300 K), characteristic of slightly Zn-enriched ZnSe. The intensity of the self-activated bands is shown to increase as the concentration of dissolved oxygen increases.

Etching behavior of CVD zinc selenide in inorganic acid solutions

Chemical interaction between polished surfaces of polycrystalline zinc selenide and inorganic acid solutions of various concentrations has been studied.

Absorption Spectrum of ZnO Precipitates in ZnSe

The absorption spectrum of ZnO precipitates in ZnSe saturated with oxygen is studied in the spectral range 500–2000 cm–1 and is shown to correlate with the transmission spectrum of single-crystal ZnO. Saturation of ZnSe with oxygen in the course of growth leads to ZnO precipitation during cooling. The precipitates give rise to narrow absorption bands in the range 5.8–7.1 μm, which correlate with the components of the multiphonon absorption spectrum of ZnO, formed by combinations of LO and TO phonons. The 2LO mode defines the long-wavelength transmission edge of ZnO. In addition, the spectrum shows strong absorptions due to the LO + TO(10.2 μm) and 2TO (∼11.3 and 12.7 μm) modes. The possible role of SeO2 is discussed. It is suggested that ZnO with a high carrier concentration may act as a “gray” filter in the spectral range 2–9 μm.

Effect of magnesium aluminum isopropoxide hydrolysis conditions on the properties of magnesium aluminate spinel powders

We have studied the influence of the conditions of hydrolysis of the magnesium aluminum double alkoxide MgAl2(OPri)8 and the heating rate and calcination temperature of aluminum magnesium hydroxides on the particle size and morphology of magnesium aluminate spinel powders. Conditions of the two-step process have been identified that make it possible to reproducibly prepare MgAl2O4 nanopowders with controlled properties. We have obtained MgAl2O4 powders ranging in specific surface area from 2 to 160 m2/g.

Studies of the infrared luminescence of ZnSe doped with copper and oxygen

The results of studying the poorly understood 700-to 2000-nm spectral region in ZnSe cathodoluminescence of condensates deposited from the vapor phase with deviations from stoichiometry and Cu and O introduction into a pure matrix are reported. The nature of cathodoluminescence in the region of 1300–1400 nm is refined: the conclusion is drawn that the emission is caused by isolated VZnI(II) vacancies. The behavior of VSe-related luminescence bands at 830 and 960 nm, when the matrix composition changes, is considered.