Compositionally graded InAlAs buffers grown by metal-organic chemical vapor deposition are impaired by phase separation occurring at In content higher than 35%. Phase separation results in rough epilayers with poor crystalline material quality. By introducing low temperature grown InGaAs interlayers in the compositionally graded InAlAs buffer, the surface roughness decreases, allowing a grading of up to In0.60Al0.40As without any phase separation occurring. This composite buffer is applied to fabricate a 200 mm diameter InP-on-Si virtual substrate with a threading dislocation density around 1 x 10(8) cm(2). (C) 2017 Elsevier B.V. All rights reserved.