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 metall o-organic vapour-phase epitaxy (MOVPE) environment by reflectance anis otropy spectroscopy (RAS) and in the UHV chamber also by low energy el ectron 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 hydrog en-terminated surface were observed. Independent of the surface recons truction the RAS spectrum always exhibited a peak at 3.45 eV with a ha lf-width of 100 meV. The height of this peak increases with increasing misorientation towards [011] and vanishes for on-axis wafers. By anne aling up to 560-degrees-C the RAS signal nearly disappears in correlat ion with the desorption of the hydrogen. Under MOVPE conditions (H-2 c arrier gas at 100 mbar), reflectance anisotropy spectra similar to tho se measured under UHV conditions are obtained. Simulating the first st ep 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 de posited on the surface. The corresponding reflectance anisotropy spect rum with a double-peak structure resembles that found after depositing 1 monolayer of arsenic under molecular beam epitaxy conditions. Refle ction high energy electron diffraction showed in the latter case a dou ble-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 sign al seems to be furthermore correlated with the presence of Si-H bonds or Si-As bonds.