Surface reconstruction on semiconductors

Abstract

Reconstruction of semiconductor surfaces is considered in a tight-binding framework using the bond orbital approximation to simplify the total energy calculation. A Jahn-Teller type of distortion, based upon a dehybridization of the dangling hybrids, is found to dominate and to lead to distortions larger than those customarily proposed at surfaces. This result, together with experimental knowledge of the surfaces, leads to specific forms for the reconstruction expected on the principal symmetry surfaces of both polar and nonpolar semiconductors. The forms found for (111) and (110) silicons surfaces are among forms which have been proposed earlier, but a canted ridge structure for the (100) surface is new. The reconstruction is large enough to drop the occupied dangling hybrid state deep into the valence band, suggesting that observed structure near the top of the valence band is due to back bonds, in agreement with Pandey and Phillips. The reconstruction also tends to increase the work function above the unreconstructed value on all surfaces. The effect of adsorption of atoms on the reconstruction as a function of the valence of the adsorbate, is summarized. It is found that while the energy to form a vacancy on a silicon (111) surface is very large, silicon atoms outside the nominal surface should be quite stable. This suggests that the 7 × 7 reconstruction is a pattern of add-atoms rather than (and topologically unrelated to) a pattern of vacancies.