Suppression of dislocation accumulation in GaAs film on Si substrate by combination of impurity doping and selective are
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Dislocation accumulation in gallium-arsenide film, which is deposited on silicon substrate and cooled down from the deposition to room temperature, is examined by crystal plasticity simulation. A new approach to suppression of dislocation accumulation is proposed such that selective growth of the film and partial doping of impurities into it are combined. The results show the possibility to localize the plastic deformation near the film/substrate interface and to keep the surface region of the film almost dislocation-free. Geometry of the selectively grown film and a strategy for partial doping of impurities, which suppresses the dislocation accumulation in the surface region of the film, are considered. I. INTRODUCTION The heteroepitaxial growth of GaAs film on Si substrate has been attracting much interest since it offers a possibility to construct optical and optoelectronic devices by combining merits of Si and GaAs. However, adoption of the heterostructure is accompanied by some problems. That is, in the GaAs film which is grown on Si substrate, thermal stress is generated on cooling due to the difference in thermal expansion coefficients between the two. As a consequence, a high density of dislocations is accumulated,1'2 making light emission from the GaAs film low and emission lifetime short compared to that obtained from bulk GaAs materials. An in situ observation of the dislocation density in the film3 shows that the density of dislocations changes from 10 8 /nr 2 at the deposition temperature to 10 n " 12 /m" 2 after cooling down to room temperature; this indicates that the dislocation accumulation results from the generation of thermal stress during cooling. In recent years, there have been many studies of ways to avoid dislocation accumulation in the film, including in situ annealing,4 introduction of a strained layer superlattice,5 selective film growth,6'7 partial film separation,8'9 low temperature growth,10 and stress balance.11 The dislocation density after cooling achieved by such techniques ranges from 108 to 10 9 /nT 2 . In order to realize GaAs/Si devices at a satisfactory reliability level, it is necessary to develop a film growth technique by which the dislocation accumulation can be controlled at an acceptable rate of film growth. In this paper we propose a new technical concept of film growth which combines selective area growth of film and impurity doping. Through selective area growth67'12"14 the thermal stress in the vicinity of the film surface is released by the effect of a free surface. The stress distribution changes with the geometry of 3032
J. Mater. Res., Vol. 7, No. 11, Nov 1992
http://journals.cambridge.org
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the film cross section and the effect of stress release is significant when the width-to-thickness ratio of the film cross section is smaller than 10. Doping of impurity atoms15"18 into the film allows control of the movement of dislocations. Combination of the selective area growth of the film with the effect of impurity doping makes it possible to
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