X-ray topography of lattice relaxation in strained layer semiconductors: post-growth studies and a new facility for in situ topography during MBE growth

Abstract

The ability of X-ray topography to image individual dislocations makes it an ideal tool with which to investigate the initial stages of lattice relaxation in strained-layer semiconductors. Topographs provide a useful insight into the origin of the first misfit dislocations, which define the critical thickness, and make possible quantitative analysis of the initial strain relaxation process. Examples are given for the InxGa1-xAs/GaAs and In1-xAlxSb/InSb materials systems. In the second case the rate of increase in misfit dislocation density with layer thickness is substantially lower. This is believed to be due to the different substrate dislocation densities of GaAs (>104 cm-2) and InSb (<102 cm-2). The early success of these experiments has led to the development of an MBE facility which allows X-ray topography during the growth and post-growth processing stages of the materials. The system is described and the potential benefits over ex situ studies are discussed.