Comparison of Interface Formation for GaAs-on-Si and ZnSe-on-Si
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COMPARISON OF INTERFACE FORMATION FOR GaAs-on-Si AND ZnSe-on-Si.
R. D.BRINGANS* and MARJORIE A. OLMSTEADt * Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304 t Department of Physics, University of California, Berkeley, CA 94720
ABSTRACT A comparison is made between the interface formed when GaAs is grown heteroepitaxially on Si(100) substrates with that formed for ZnSe-on-Si(100) growth.
Results of core level
photoemission spectroscopy show that the Si(100) surface reacts with As atoms to form a stable monolayer, but reacts with Se atoms to form the compound SiSe 2. Annealing treatments can also give rise to a submonolayer coverage of Se atoms on Si(100). The SiSe 2 compound is also seen at the interface between ZnSe and Si. Island formation appears to occur at the beginning of growth for both GaAs-on-Si and ZnSe-on-Si INTRODUCTION The occurrence of island formation at the beginning of GaAs-on-Si heteroepitaxy is very likely related to the propagation of dislocations to the surface of the GaAs layer. The large density (106 2
to 108 cm- ) of these threading dislocations which reach the surface of the GaAs film after several
microns of growth remains one of the main problems in GaAs on Si heteroepitaxy. In this paper we compare the interface formed for ZnSe growth on Si with the more widely studied case of GaAs-onSi in order to examine the chemical driving forces for island formation. We begin by comparing the interaction of As and Se atoms with the Si(100) surface and find significant qualitative differences. Then we examine how this difference is manifested in differences in the interface chemistry between Si(1 00): GaAs and Si(1 00):ZnSe. EXPERIMENTAL DETAILS The Si substrates were cleaned in ultra high vacuum and their cleanliness and surface order determined by ultra-violet photoemission (UPS) or angle-resolved photoemission (ARPES) and low energy electron diffraction (LEED). The arsenic-terminated surfaces were prepared by annealing the cleaned and well-ordered surfaces in a flux of As4 molecules from a molecular beam epitaxy effusion cell [1]. An electrochemical cell was used as the source for selenium. The thin GaAs films were produced in situ by molecular beam epitaxy (MBE), using elemental As and Ga sources. A compound source was used to grow the ZnSe layers. Annealing Si(100):ZnSe films to around 500 0C was then found to remove all of the Zn atoms but leave a thin film of Se atoms, and this was used as an alternative method to produce submonolayer Se films. Mat. Res. Soc. Symp. Proc. Vol. 145. ©1989 Materials Research Society
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COMPARISON OF BONDING OF As AND Se TO Si(100) One of the dominant effects in the heteroepitaxy of GaAs on Si is the strong bonding that takes place between As and the Si(100) surface. This is due to the fact that the addition of As-As dimers to the surface leaves all atoms fully coordinated and relatively unreactive [2]. The structure of this surface, which was deduced from total energy calculations and angle-resolved photoemission measurements o
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