Low-temperature Si/Si_1-xGe_x/Si heterostructure growth at high Ge fractions by low-pressure chemical vapor deposition

The growth of a Si/Si_1-xGe_x/Si heterostructure at high Ge fractions was investigated by an ultraclean low-pressure chemical vapor deposition using SiH₄ and GeH₄ gases in the temperature range of 450-650°C. It was found that a lowering of the deposition temperatures of the Si_1-xGe_x and Si capping layers is necessary with the increasing Ge fraction in order to prevent island growth of the layer during deposition. For a Ge fraction around 0.2, atomically flat surfaces and interfaces can be obtained by depositing Si_1-xGe _x and Si capping layers at 550°C. For higher Ge fractions, even much lower deposition temperatures are suitable, namely 450°C for a Si _0.3Ge_0.7 layer and 500°C for a Si_0.5Ge _0.5 layer, respectively, with a Si capping layer deposited at temperatures of 550°C or less. Nevertheless, the degradation of the Si _0.3Ge_0.7 layer with the capping layer was not observed even after a wet oxidation at 700°C.