Growth of abrupt Ge layers in Si (100)

Abstract

We have studied the growth of pseudomorphic Ge layers sandwiched in Si (100) using Raman spectroscopy and medium energy ion scattering spectrocopy. We find that films deposited at temperatures between {reversed tilde} 550 and {reversed tilde} 350°C while commensurate, do not have atomically sharp interfaces. However, films deposited at {reversed tilde} 250°C have atomically sharp interfaces and are still commensurate. Any further lowering of growth temperature leads to Raman spectra similar to those obtained from amorphous layers. This is consistent with the observed deterioration of the low energy electron diffration pattern from sharp to diffuse after growth. These results are corroborated by medium energy ion scattering done at 350 keV using He+. For samples grown at ≥250°C channeling yields were below 3%. For samples grown at temperatures above 450°C an asymmetric broadening of the Ge peak into the capping Si layer is seen. This may be explained either by interfacial roughening of the Ge-Si interface nearer the surface, or by surface enhanced mixing of Ge into the capping Si layer. Our results show that: (1) Raman spectroscopy is an extremely sensitive tool to study order in such SimGen structures and is well corroborated by structural measurement techniques; (2) optimal growth temperatures for such structures are considerably lower than commonly believed and that the growth temperature window is somewhat narrow; (3) important differences exist between the growth of Ge on Si and the growth of Si on Ge. © 1989.