6H- AND 4H-SiC(0001) SiSURFACE RICHNESS DOSING BY HYDROGEN ETCHING: A WAY TO REDUCE THE FORMATION TEMPERATURE OF RECONSTRUCTIONS

In 6H- or 4H-SiC(0001) surface technology, a Si-rich 3 × 3 reconstruction is usually first prepared by heating at 800°C under Si flux, and two other most stable$\sqrt{3}\times\sqrt{3}\ {\rm R}30^\circ$or$6\sqrt{3}\times 6\sqrt{3}\ {\rm R}30^\circ$reconstructions are obtained by further extensive annealing at higher temperatures ranging between 900 and 1250°C. The 3 × 3 Si excess is thus progressively depleted up to a graphitized C-rich surface. By crystallographic (LEED) and chemical surface characterizations (XPS and UPS), we show that all these reconstructions can be obtained at a unique, low formation temperature of 800°C if the Si richness is controlled before annealing. This control is achieved by exposing the 3 × 3 surface to atomic hydrogen at room temperature. This procedure allows one to etch or partially deplete the (3 × 3)-associated Si excess, and make it more comparable to the final Si coverages, required to form the less Si-rich$\sqrt{3}\times\sqrt{3}\ {\rm R}30^\circ$or$6\sqrt{3}\times 6\sqrt{3}\ {\rm R}30^\circ$reconstructions. After annealing at 800°C, the latter reconstructions are no longer determined by the heating time or temperature but only by the initial Si coverage set by the H doses inducing the low temperature etching. The high temperature treatment, required to remove by sublimation a significant Si amount associated with the Si-rich 3 × 3 reconstruction, is thus avoided. Such a methodology could be applied to other binary systems in the formation of reconstructions that depends on surface richness.