Study of semiconductor heterointerface using low-energy electron transmission spectroscopy

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Initial stages of Ge growth on Si and its heterointerface have been investigated using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and low-energy electron transmission spectroscopy (LEETS).For Ge growth on Si(001) surface, LEED and AES measurements reveal that up to a coverage of 5ML, Ge growth proceeds in the pseudomorphic layer-by-layer fashion. Beyond a coverage of 5ML, small 3D clusters with {015} facets grow epitaxially keeping the substrate orientation. Moreover, energy dependence of the LEED spot profiles reveals that the lattice distortion still remains in this phase consisting of small 3D clusters.When growing on Si(111) surface with an As surfactant, up to a coverage of 8ML, Ge growth proceeds in the pseudomorphic layer-by-layer fashion. Further deposition of Ge leads to the relaxation of lattice misfit and growth of Ge films having the same lattice constant as bulk Ge. In contrast, Ge growth without the As surfactant proceeds in the Stranski-Krastanov mode. LEED measurements reveal that Ge islands have the smaller lattice constant by 1.5% than that of bulk Ge. We believe that the resulting island is an alloy of Si and Ge, since growth temperature is high (500ﾟC) and growth rate is very slow (0.07ML/min). Based on the results, we speculate that the As surfactant prevents the alloying of growing films.LEET measurements have been employed for Ge films grown on both Si(001) and Si(111) surfaces. For Ge growth on Si(111) at 500ﾟC with the As surfactant, LEET spectra exhibit characteristic quantum size features, suggesting the abrupt Ge/Si interface. In contrast, when growing not only on Si(001) but on Si(111) at 600ﾟC with the As surfactant, no quantum feature characteristic of LEET spectra was observed. These results indicate that LEETS provides information on the structure of semiconductor heterointerfaces.