Comparison of the crystalline quality of step-graded and continuously graded InGaAs buffer layers

In this paper we summarize work carried out to investigate the relaxation of epitaxial strained layers of InGaAs on GaAs, where the InGaAs composition has been increased throughout the layer in either a stepwise or linearly graded form. The results are presented from the viewpoint of exploiting the relaxed layers to provide prescribed in-plane surface lattice parameters for subsequent use as ''virtual'' substrates for novel devices. We compare the behaviour of step-graded and linearly graded InGaAs layers, We consider the crystalline quality of different structures and discuss the design requirements for subsequent device quality growth.