Photoluminescence Of Zincselenide Single Crystals Annealed In Zinc Or Selenium Atmosphere
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Kenji Yoshino, Yasushi Matsushima, Hiroyoshi Kinoshita and Makoto Hiramatsu College of Liberal Arts and Sciences, Okayama University, 2-1-1 Tsushima-naka, Okayama, 700, Japan
ABSTRACT Zincselenide single crystals grown by the sublimation method are annealed in Zn or Se atmosphere. The annealing effects are examined by means of photoluminescence (PL) and reflection spectroscopy at 4.2 K. In the PL spectrum for the as-grown crystal, bound exciton lines (12, I1)are observed. For the Zn-annealed crystal, the free exciton line is clearly observed. For the Se-annealed crystal, peak positions of all lines shift to the higher energies and all lines become sharp, compared with the spectra for the as-grown crystal. It is concluded that Sc-vacancies affect the bandgap energy more than Zn-vacancies do.
INTRODUCTION Optical and electrical properties of ZnSe single crystals have been widely investigated because of the need for blue-emitting devices [1-14]. Bulk crystals with low electrical resistivity are needed as the substrate for growing crystals by molecular beam homoepitaxy (MBE). Many investigators reported on the methods for growing ZnSe crystals such as the Bridgeman method, solution growth method and iodine transport technique [10-14]. The sublimation method is simple and effective for refining impurities in the crystal. It is difficult, however, to hold stoichometry of
ZnSe single crystals grown by the sublimation method because of the difference between the vapor pressure of Zn and that of Se [15]. In this work, we prepared ZnSe single crystals by the self-closed method which is a type of sublimation method. Crystals were annealed in Zn and Se atmospheres. Some annealed crystals were annealed again :The Zn-annealed crystals were annealed in the Se atmosphere. On the other hand, the Se-annealed crystals were annealed in the Zn atmosphere. The annealing effects are examined by observing photoluminescence (PL) and reflection spectra in the bandedge region.
EXPERIMENTAL PROCEDURE Zincselenide single crystals were grown by the sublimation method. Zincselenide powder (6nine purity, supplied from G. E. Co. Ltd.) which was used as the starting material was heated in a stream of argon gas (0.1 1 / min.) at 1000 *C for 24 h. The crystallized ZnSe powder was put in a quartz ampoule (10 mm in diameter, 30 cm long). The ampoule was inserted into an electric furnace made by Shimazu Kinzoku Co. Ltd. The schematic construction and the temperature distribution of the furnace are shown in Fig. 1. During the crystal growth, the temperature of the necked part of the ampoule was kept at 1050 °C and that of the closed side of the ampoule was kept at 1250 °C (Fig. 1). This temperature difference of about 200 °C was the best condition. The ampoule was heated for 96 h in a stream of argon gas. The average size of the obtained ingot was 533 Mat. Res. Soc. Symp. Proc. Vol. 348. 01994 Materials Research Society
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Distance from edge (cm) Fig. 1 The schematic construction of
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