Kenzo Igaki

Bound-Exciton Luminescence of Cu-Doped ZnSe

As an experimental approach to clarify the correlation between doped impurity and native defects, copper was deped at a low temperature to high-purity ZnSe crystals with controlled deviation from stoichiometry by a previous heat treatment under molten Zn or saturation pressure of Se. Photoluminescence was measured and examined as a function of deviation from stoichiometry. The site selection doping of Cu was achieved by controlling native defect concentrations. I1deep lines are known to arise from acceptors of two different origins, VZn and CuZn.

The Electrical Properties of Zinc Selenide Heat-Treated in Controlled Partial Pressures of Constituent Elements

ZnSe single crystals, some of which had been previously heat-treated in molten Zn or doped with Cu, were heat-treated in Zn or Se vapor. The Hall effect and the electrical conductivity were measured and examined as a function of the vapor pressure. Conduction after heat treatment in Se vapor is considered to be dominated by Zn vacancies, Se interstitials, or associated defects containing one of these, while the high n-type conductivity observed after heat treatment in Zn vapor is dominated by Se vacancies or Zn interstitials. With decrease of the acceptor impurity concentration, the transition vapor pressure from low to high conductivity shifts from a high Zn vapor pressure to a low one corresponding to the total pressure minimum.

Photoluminescence spectra of high purity zinc selenide single crystals

Abstract High purity zinc selenide single crystals have been grown by a vapor phase transport method, using a commercial grade high purity selenium and the zinc purified by vacuum distillation and overlap zone-melting. Photoluminescence spectra measured on the grown crystals are confirmed to be affected considerably by the purity of zinc used and show that the crystals are of good quality. After the Zn-dip treatment, the Id1 line disappears, the peak energy of Ex decreases from 2.8024 to 2.8019 eV, and the emission intensities of Ex-LO and Ex-2LO become strong. The notable spectral feature observed on the purest crystal is that the emission intensities of the I3 lines become stronger than those of the I2 lines. For some of the crystals, a new emission band is found at 2.8002 eV and its intensity is found to be non-linearly dependent upon the excitation intensity.

Orange Luminescence in CdS

The characteristics of orange (O) luminescence in undoped CdS were examined by observing the energy shift of the emission peak as a function of composition in two kinds of solid solution, CdSxSe1-x and CdyZn1-y S. Different behaviors of the O-bands were observed in these solid solutions. The O-emission in CdS is thermally quenched at about 200 K with an activation energy of 0.21 eV. From the results, the emission mechanism was explained as D(donor)-A(acceptor) pair recombination with the donor level 0.21 eV below the bottom of the conduction band and the acceptor level 0.29 eV above the top of the valence band. The donor responsible for the emission seems to be related to native defects such as Cd interstitials or S vacancies.

Photoluminescence and Electrical Properties of Undoped and Cl-Doped ZnSe

Undoped and Cl-doped ZnSe specimens were heat-treated in Zn or Se vapor, or in molten Zn, and the photoluminescence spectra and electron concentration of the specimens were measured. Several new emissions were observed in high-purity ZnSe with Cl concentration ([Cl]) lower than 1015 cm-3 while SA-emission band and a IDEEP1 line were observed in ZnSe with [Cl]>1015 cm-3 heat-treated in molten Zn. The former was observed to increase with [Cl] and with the Zn vapor pressure, and the latter to increase with [Cl]. The electron concentration at room temperature was proportional to [Cl] for [Cl]<1017 cm-3. This paper proposes a model explaining these effects on the [Cl] dependence of the concentration of defects, ClSe donors, SA-centers (VZnClSe) and V-Zn.

Vapor phase transport of cadmium telluride

Abstract Cadmium telluride crystals were grown by the sublimation method under an independently-controlled partial pressure of one of the constituent elements. A reservoir chamber at one end of the closed quartz tube is used to control the partial pressure. When the partial pressure in the reservoir chamber is high, the transport rate is strongly dependent on the partial pressure; proportional to the (-3/2)th power of Te 2 partial pressure for the tellurium reservoir or proportional to the (-3)rd power of Cd partial pressure for the cadmium reservoir. In these cases the transport rate depends upon the average temperature gradient and is known to be rate-determined by the diffusion process in the vapor phase. With decreasing partial pressure in the reservoir, the transport rate becomes independent of partial pressure but is determined by the temperature difference between the source chamber and the growth chamber. Furthermore, it is found to be proportional to the surface area of the source specimen or to the condensation area. In these cases either the evaporation or the condensation process is rate-determining.

Preparation of high purity cobalt

Abstract A combination of anion exchange separation, electrolytic extraction, floating zone refining and dry hydrogen treatment was used to purify cobalt. The effectiveness of each purification process was confirmed by measurements of the residual resistivity ratio (RRR) and activation analyses. Proton activation analysis revealed that all the main metallic impurities except iron were effectively removed by a combination of these processes. The effective removal of oxygen, nitrogen and carbon by dry hydrogen treatment was confirmed by activation analyses using 3 He ion beams, proton beams and γ rays. It was found that the rate-controlling step in the decarburization process was a surface reaction. The maximum RRR obtained for the purified specimen was 334, which is higher than previously reported values.

Preparation of high purity zinc selenide single crystals and evaluation through photoluminescence spectra

Abstract High purity zinc selenide single crystals have been grown using commercial high purity selenium and zinc purified by vacuum distillation and overlap zone-melting. The photoluminescence spectra measured at 4.2 K on the grown crystals are confirmed to be affected considerably by the purity of the zinc used. In the case of the purest crystal, the emission intensity related to donor bound excitons is remarkably small compared to that due to the recombination of free excitons. Moreover, no emission band is observed in the phonon energy below 2.4 eV.

Proton activation analysis of trace impurities in purified cobalt

Nondestructive activation analysis by proton beam bombardment has been applied to cobalt specimens. Thick target yields were measured on 18 elements for the purpose of quantitative analysis. In order to detect precisely the radionuclides with different half-lives, gamma-ray spectrometry was repeated three times after different cooling times of 1, 15 and 250 hrs from the finish of bombardment for 1 hrby 10.4 MeV proton beam. It was found that Ti, Cr, Fe, Ni, Cu, Zn, Ga, Ge, As, Se, Zr, Nb, Mo, Cd, Sn, Sb, and Te of the order of ppm or less could be detected accurately. Using the proton activation analysis developed, the purification effects of anion exchange, electrolytic extraction, and floating zone-refining have been examined. It was confirmed that the concentrations of the impurity elements contained in the starting material decreased stepwise upon the application of each purification method.

Millimeter and Submillimeter Cyclotron Resonance Study of High-Purity ZnSe

We have observed for the first time the electron cyclotron resonance in a high quality ZnSe crystal, using both millimeter and submillimeter waves. We obtain an isotropic effective mass m*=0.145m0. From linewidth measurement it is found that the cyclotron mobility at 4.2 K exceeds 2.3×105 cm2/Vs. A strong anisotropy in absorption intensity has been observed in 35 GHz measurement.