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ATOMIC LAYER EPITAXY OF WIDE BANDGAP II-VI COMPOUND SEMICONDUCTOR SUPERLATTICES M.Konagai,

Y.Takemura, R.Kimura, N.Teraguchi and K.Takahashl

Tokyo Institute of Technology, Dept. of Electrical and Electronic Engineering, 2-12-1, Ohokayama, Meguro-ku, Tokyo 152, Japan ABSTRACT ZnSe, ZnTe and ZnSe-ZnTe strained-layer superlattices (SLS's) have been successfully grown by atomic layer epitaxy (ALE) using molecular beam epitaxy (MBE-ALE). The ideal ALE growth, i.e., one monolayer per cycle of opening and closing the shutters of the constituent elements, was obtained for ZnSe in the substrate temperature range of 250-350 0 C. However, for ZnTe, precise control of the Te beam intensity is needed to obtain the ALE growth. Optical properties of the (ZnSe)l-(ZnTe) 1 SLS were evaluated by photoluminesence. ZnSe films were also grown by ALE using metalorganic molecular beam epitaxy (MOMBE-ALE). Diethylzinc (DEZn), diethylsulfur (DES) and diethylselenium (DESe) were used as source gases for Zn, S and Se, respectively. The ALE growth of ZnSe was achieved at substrate temperature between 250 and 300 0 C which is about 150 0 C lower than that for the conventional MOMBE. INTRODUCTION II-VI compound semiconductors, especially strained-layer superlattices (SLS's) consisting of ZnS, ZnSe and ZnTe, are promising for light emitting devices in the visible wavelength region. We have been investigating the properties of ZnSe-ZnTe SLS's prepared by MBE for several years and obtained the following results: (1) The luminesence color changes from blue-green to red by tailoring the structure of the superlattice [1]. (2) The lattice mismatch in the SLS's is accommodated by tetragonal distortion of the crystal lattices of the constituent materials with the thickness below the critical layer thickness [2]. (3) The SLS with modulation doping of ZnTe with Sb and ZnSe with Ga exhibit p- and n-type conductivity, respectively, with a carrier concentration of about 1x10 14 cm- 3 [3]. However, the obtained carrier concentration is still too low for practical device applications. We have clarified factors degrading the SLS quality [4,51. The factors degrading optical and electrical properties of the SLS's are (1) structural degradation at growth temperature (interdiffusion);(2) thermal diffusion of impurities in the SLS's and (3) poor interface abruptness and uniformity and irregularity in the superlattice period. We have found that the interdiffusion of the constituent materials and the thermal diffusion of impurities were not main factors degrading electrical properties. To solve the third problem, atomic layer epitaxy was employed to grow SLS's [6]. In this paper, we present the detailed ALE growth conditions of ZnSe and ZnTe and growth of ZnSe-ZnTe SLS's. In the ZnSe-ZnTe SLS systems their photoluminescence(PL) peak energies cover the region from blue-green to red. However, to obtain much shorter wavelength, for pure blue color, we have to use S. In MBE, if we use two different kinds of high vapor pressure source materials, especially S and Se, we su