Initial stages of interface formation in Group IV-IV systems: Sn on Ge(100) and Ge(111).

The initial stages of interface formation between an ultrathin layer of Sn and the Ge(100)c2X4 and Ge(111) c2X8 surfaces are studied under atomically clean conditions in ultra-high vacuum. The growth mode is investigated using Auger electron spectroscopy in conjunction with Rutherford backscattering (RBS) techniques. A complex behavior is found: Below a certain critical coverage theta(c)(1.15(.)10(15)cm(-2)) the Sn deposits in a laminar fashion for a temperature range from 150K to 700K. For coverages beyond theta(c) the growth mode is temperature dependent. At 150K best agreement is found with the data assuming a laminar growth mode. At room-temperature Stranski-Krastanov growth is dominant, whereas elevated temperatures lead to successively more severe indiffusion. The Sn deposition begins to order the substrate reconstruction on both surfaces below theta(c), however reordering is not complete. The identical ordering behavior observed for Ge(100)c2X4 and Ge(111)c2X8 is compared with the behavior of Si(100)2X1 and Si(111)7X7 and discussed in terms of the topography of these surfaces.