Abstract
The strain relaxation behaviour of and oriented InxGa1-xAs layers grown on GaAs substrates has been investigated using surface profilometry and high resolution X-ray diffraction. The strain relaxation behaviour of single InxGa1-xAs layers (grown by various methods) has been studied using double crystal X-ray diffraction. The layer strain has been shown to be predictable, following the empirical relaxation law given by epsilonr = k/d where epsilonr is the residual strain, d is the layer thickness and k is a constant (= 0.84 nm +/- 0.18 nm). In addition, it is shown, using previously published data, that this law is applicable to other semiconductor alloy systems. Results show that the relaxation behaviour of oriented material is very similar to that of oriented material. However, the critical thickness is 1.23 times that for material in agreement with theory. It is shown that plastic relaxation of good quality epitaxially strained layers is accompanied by roughening of the surface in the form of striations and that the maximum striation height is always less than 20 nm regardless of layer thickness. Measurements of strain relaxation in multi-quantum well type samples show good agreement with a simple geometric theory in which the minimum barrier thickness needed to decouple strained layers of thickness hw is given as 0.62hw.