Relaxed GeSi alloy grown on low-temperature buffers by MBE

Abstract

ABSTRACT We have developed a new MBE growth technique by using low-temperature-Si (LT-Si) or LT-GeSi buffer layers. Even ifthe Ge fraction up to 90%, the total thickness of fully relaxed GeSi1 buffers can be reduced to 1 .7 tm with dislocationdensity lower than 5x 106 cm2. The roughness is no more than 6 nm. According to the analysis of X-ray diffraction, the crystal quality of the top layer is very good, and the strain relaxation is quite inhomogeneous from the beginning of relaxation. By using high resolution cross section TEM, we observed that stacking faults are induced and form the misfitdislocations in the interface of GeSi/LT-Si. We propose that the formation of the stacking faults is due to the aggregation ofthe large amount ofthe vacant defects in the LT-Si layer.Keywords: dislocation, stacking faults, vacancy, strain relax, silicon, germanium 1. INTRODUCTION Some GeSi/Si heterostructures devices require relaxed GeSi buffers to serve as virtual substrates. Unfortunately, 4% oflattice mismatch often results in high threading dislocation (TD) density even up to 10' cm2. [1][2] Therefore, to decrease theTD density has attracted great attention. Among various techniques used, the compositionally graded buffer seems to be avery useful one by which the TD density can be reduced to as low as I 06 cm2. E3][4] However, such buffers are usually verythick and the surface corrugation is serious with an amplitude of up to 15-2Onm, and the Ge composition can not be higherthan 0.5 under the TDs density less than iO cm2.We have developed a new MBE growth technique, by which, relaxed, thin, and uniform GeSi layer with low TDs density isgrown on low-temperature-Si (LT-Si) or LT-GeSi buffer layers.