RELAXED GEXSI1-X STRUCTURES FOR III-V INTEGRATION WITH SI AND HIGH MOBILITY 2-DIMENSIONAL ELECTRON GASES IN SI

To obtain a large lattice constant on Si, we have grown compositionally graded GexSi1-x on Si. These buffer layers have been characterized with electron-beam-induced current, transmission electron microscopy, scanning electron microscopy, x-ray diffraction, and photoluminescence to determine the extent of relaxation, the threading dislocation density, the surface morphology, and the optical properties. We have observed that it is possible to obtain completely relaxed GexSi1-x layers with 0.1 < x < 1, threading dislocation densities of 10(5)-5 X 10(6) cm-2 , and with bulk GexSi1-x optical properties. Calculations show that gradually graded layers grown at relatively high temperatures can remain in equilibrium throughout growth, thereby avoiding strain buildup and the introduction of more threading dislocations through dislocation nucleation. It is also shown that the degree of surface crosshatch is related to inhomogeneous strain fields in the epilayer and to the thickness at which dislocations are introduced. These relaxed buffers have been used for the fabrication of very high mobility two-dimensional electron gases in Si and also as templates for lattice-matched III-V growth. We have obtained electron gases in Si with mobilities as high as 170 000 cm2/V s and red-emitting InGaP light emitting diodes on Si with less than 20-mu-A reverse current at -6 V bias.