Metal/semiconductor interfaces on SnO2(110)

Interfaces formed by tin and palladium deposition on the (110) face of tin dioxide, SnO2 (a semiconductor due to native defects), have been studied from coverages of 0.05 monolayer (ML) to over 10 ML. The structural, chemical, electronic, and electrical properties of the surfaces were characterized primarily by low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy, ultraviolet photoemission spectroscopy, and a retractable four-point conductivity probe. Modifications of the substrate by oxidation, annealing, and ion bombardment treatments produced three different substrate structures which were used to examine the interface abruptness and the metallization due to Sn and Pd. The deposition of Sn produced an increased surface conductivity on the ordered substrates due to the formation of donor states (oxygen vacancies) at the surface. The deposition of Pd results in the growth of a metallic layer beginning at 1–5 ML, depending upon the surface oxygen concentration. The metallic conductivity rapidly increases with Pd coverage and by 10 ML, LEED reveals microcrystallites in azimuthal registry with the substrate. In contrast, the development of metallic conductivity is relatively slow for the disordered Sn multilayers.