Growth of Lattice-Matched ZnSe-ZnS Strained-Layer Superlattices Onto GaAs as An Alternative to ZnSSe Alloys
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GROWTH OF LATTICE-MATCHED ZnSe-ZnS STRAINED-LAYER SUPERLATTICES ONTO GaAs AS AN ALTERNATIVE TO ZnSSe ALLOYS H.ONIYAMA, S.YAMAGA AND A. YOSHIKAWA Department of Electrical and Electronics Engineering, Faculty of Engineering, Chiba University, 1-33, Yayoi-cho, Chiba 260
ABSTRACT This paper describes the results of the first attempt to reduce misfit dislocations in epilayers of a wide bandgap II-VI semiconductor on GaAs substrates by utilizing the ZnSe-ZnS strained-layer superlattice (SLS) structure. From a theoretical calculation, SLSs consisting of a 200A-ZnSe and a IOA-ZnS layer in one period can be grown as lattice-matched films to GaAs substrates. It has been found from the photoluminescence measurements and electron-beam-induced-current (EBIC) image observations that the generation of misfit dislocations can be markedly reduced, as expected.
Introduction Zinc selenide is a semiconductor with a direct wide bandgap of 2.67eV at room temperature (R.T.) and is a promising material for the fabrication of blue-light emitting devices. However. several problems must be solved to realize such devices. One of these problems is that caused from the lattice mismatch between ZnSe and substrates. ZnSe epilayers are usually grown on GaAs substrates which have a little lattice mismatch of 0.26 % (at R.T.) with ZnSe, since "substrate-quality" ZnSe bulk crystals can not be obtained at present. Although the lattice mismatch is as small as 0.263 at R.T., it is well known that it causes misfit dislocations which degrade the quality of ZnSe epilayers. For instance, such dislocations create trapping centers and/or deep luminescence centers in ZnSe epilayers. [1] In order to control electrical and optical properties of ZnSe films, the problem arising from the lattice mismatch must be overcome. The way to solve this problem is to lattice-match epilayers to GaAs substrates. Many attempts to grow lattice-matched ZnSSe alloys onto GaAs substrates have been carried out [2] , [3], [41. We propose a new idea to overcome the problem caused from lattice mismatch, utilizing the ZnSe-ZnS superlattice structure as an alternative to ZnSSe alloys. In the case of ZnSe-ZnS superlattices (SLSs), the average lattice constant of the SLSs can be lattice-matched to GaAs when each layer thickness is Mat. Res. Soc. Symp. Proc. Vol. 161. c1990 Materials Research Society
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appropriate. Because ZnSe has a larger lattice constant and ZnS has a smaller one than does GaAs. In the present study, lattice-matched ZnSe-ZnS SLSs onto GaAs were grown by metalorganic molecular beam epitaxy (MOMBE). Photoluminescence measurements were performed to investigate the strain in the ZnSe layers of the SLSs. Furthermore, electron-beam-induced-current (EBIC) image observations were carried out to observe such defects in both the SLSs and ZnSe epilayers on GaAs. It has been found from these studies that misfit dislocations can be significantly reduced.
Experiment ZnSe-ZnS SLSs were grown by MOMBE using dimethylzinc (DMZn), H2 Se and H2 S as source materials[5], [6]. The sou
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