Chemical vapor deposition of silicon-germanium heterostructures

We report on the growth of SiGe/Si heterostructures in a commercial chemica l vapor deposition cold-wall vertical reactor using SiH4 and GeH4 gas precu rsors, and we discuss their structural quality. The machine is versatile as it operates in a wide range of temperature and pressure, allowing both the ultra high vacuum and a low-pressure-like regime. In the two growth modes, the Si and SiGe deposition rates and the Ge fraction are calibrated as a f unction of the temperature and the hydrides partial pressures. The LP-CVD r egime is appropriate for the realization of thick gradually relaxed Si0.75G e0.25/Si pseudo-substrates. The role of the grading rate (5-20% Ge/mu m) on the density of threading dislocations and the surface roughness is discuss ed. Seven-period Si0.70Ge0.30/Si superlattices were grown by UHV-CVD to stu dy the interfacial chemical abruptness and morphological roughness by means of X-ray diffraction, rutherford backscattering and transmission electron microscopy techniques. Results are strongly dependent on the growth tempera ture in the 575-625 degrees C range. (C) 2000 Elsevier Science B.V. All rig hts reserved.