Strain relaxation of graded SiGe buffers grown at very high rates

The strain relaxation in compositionally graded SiGe alloy buffers was studied as a function of growth temperature and growth rate. We have used a plasma enhanced CVD technique that we call low energy plasma enhanced chemical vapour deposition (LEPECVD) to access growth rates in the range of 0.9–3.8 nm/s at substrate temperatures between 640 and 725°C. The samples were analysed by X-ray reciprocal space mapping, transmission electron microscopy and defect etching. Despite the very high growth rate, the structural properties of the buffers are identical to buffers grown at rates one or two orders of magnitude lower. The threading dislocation density is shown to decrease significantly with increasing temperature in the investigated range.