Growth of ZnSe-Based Compounds on Ge-Terminated GaAs Surface
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ABSTRACT Growth of ZnSe-based compounds on the GaAs surface terminated by ultra-thin Ge epitaxial layer was carried out by molecular beam epitaxy and the influence of Ge layer on the growth of ZnSe was investigated. When the thickness of Ge layer was 1 atomic layer (AL), 2-dimensional growth occurred in the initial stage of ZnSe layer growth and anti-phase boundary (APB) free ZnSe layer was obtained. For Ge layer thickness of 10 AL, ZnSe grew 3-dimensionally and APBs were generated in the ZnSe layer. The crystalline quality of ZnMgSSe layer was also strongly influenced by the thickness of Ge layer. These phenomena were identified to be due to the transition of Ge surface structure from single domain to double domain with increasing Ge layer thickness. 1. INTRODUCTION ZnSe-based lasers have attracted much interest as light sources in the blue and green regions for use in high density optical disks, full color displays and many other applications. Heteroepitaxial growth of ZnSe-based compounds on GaAs substrates is commonly used for fabricating ZnSe-based lasers. It has been revealed that stacking faults are generated at the ZnSe/GaAs interface and the laser degradation is induced by the presence of such defects[i,2]. Control of the initial growth of ZnSe on GaAs surface is the most important issue for improving the property of ZnSe-based lasers. Recently, it has been pointed out that the existence of Ga-Se bonds plays an important
role in such defect nucleation[3]. Termination of GaAs surface is an attractive method for avoiding the direct absorption of Se atoms on GaAs surface. Zn irradiation onto GaAs surface is known to be an effective method to suppress the formation of Ga-Se bonds [3-5]. However, defect density as low as 104 cm-2 still exists even using Zn irradiation [5]. One of the reasons is that the GaAs surface is not completely terminated by Zn layer since the sticking coefficient of Zn atoms on the As-stabilized GaAs surface is quite low. We propose a termination of GaAs surface using ultra thin Ge epitaxial layer. Germanium is one of the most suitable candidates as an interlayer at the ZnSe/GaAs interface since the lattice constant of Ge is very close to those of ZnSe and GaAs. Additionally, Ge interlayer can be used for controlling the charge imbalance at the ZnSe/GaAs interface since Ge is a Column IVelement. However, there exists a severe problem that such an interlayer of non-polar materials will become the origin generating anti-phase boundaries in the ZnSe layer. Fundamental growth process of the ZnSe/Ge/GaAs system must be clarified to use Ge layer as an interlayer for controlling the ZnSe/GaAs interface. In this study, growth of ZnSe-based compounds on the GaAs surface terminated by ultra-thin Ge epitaxial layer was carried out and the influence of Ge layer on the growth of ZnSe was investigated. The relationship between ZnSe initial growth and the domain structure of Ge surface is discussed. 141 Mat. Res. Soc. Symp. Proc. Vol. 448 0 1997 Materials Research Society
2. EXPERIMENTAL PROCEDURES
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