HYDROGEN-TERMINATED SI(100) SURFACES INVESTIGATED BY REFLECTANCE ANISOTROPY SPECTROSCOPY

Boron-doped Si(100) wafers (1 x 10(15) cm-3) with different off-angle orientations (0, 4.5 and 6-degrees) towards [011] were prepared with a modified RCA cleaning and a 5% HF dip. The resulting hydrogen-covered surface was examined either in an ultrahigh vacuum (UHV) or -a metallo-organic vapour-phase epitaxy (MOVPE) environment by reflectance anisotropy spectroscopy (RAS) and in the UHV chamber also by low energy electron diffraction and Auger spectroscopy. Under UHV conditions the (1 x 1) (at room temperature) dihydride and the double-domain (2 x 1, 1 x 2) (at higher temperatures) monohydride reconstruction of the hydrogen-terminated surface were observed. Independent of the surface reconstruction the RAS spectrum always exhibited a peak at 3.45 eV with a half-width of 100 meV. The height of this peak increases with increasing misorientation towards [011] and vanishes for on-axis wafers. By annealing up to 560-degrees-C the RAS signal nearly disappears in correlation with the desorption of the hydrogen. Under MOVPE conditions (H-2 carrier gas at 100 mbar), reflectance anisotropy spectra similar to those measured under UHV conditions are obtained. Simulating the first step of GaAs on Si growth by adding AsH3 to the carrier gas 560-degrees-C (above the AsH3 decomposition temperature) it is found that As is deposited on the surface. The corresponding reflectance anisotropy spectrum with a double-peak structure resembles that found after depositing 1 monolayer of arsenic under molecular beam epitaxy conditions. Reflection high energy electron diffraction showed in the latter case a double-domain (2 x 1) reconstruction. The data are discussed in terms of stepped surfaces with single or double steps. While in the former the RAS signals from different terraces cancel, they add up in the case of double steps and produce a RAS signal. The appearance of the RAS signal seems to be furthermore correlated with the presence of Si-H bonds or Si-As bonds.