AVS 45th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM10
Structure of Arsenic-Passivated Germanium (100)

Tuesday, November 3, 1998, 11:20 am, Room 308

Session: Semiconductor Surface Structure
Presenter: S. Gan, University of California, Los Angeles
Authors: S. Gan, University of California, Los Angeles
L. Li, University of California, Los Angeles
M.J. Begarney, University of California, Los Angeles
D. Law, University of California, Los Angeles
C. Li, University of California, Los Angeles
B.-K. Han, University of California, Los Angeles
R.F. Hicks, University of California, Los Angeles
Correspondent: Click to Email
Arsenic passivation is an important first step in the heteroepitaxy of GaAs on Ge (100). Using scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy and low energy electron diffraction, we have identified the atomic structure of arsenic-terminated Ge (100) surfaces. The germanium substrates were exposed to arsenic in two different ways: (1) by dosing with 500 L arsine in ultrahigh vacuum, and (2) by exposure to 2.0 Torr tertiarybutylarsine and 97.0 Torr hydrogen at 650°C in a CVD reactor. During AsH3 dosing at 25 to 300°C, the As coverage is approximately constant at 0.3 ML. Upon increasing the dosing temperature further, the coverage attains a maximum of 1.0 ML at 425°C, then gradually declines to zero at 600°C. Scanning tunneling micrographs obtained at 1 ML coverage show that the surface has been transformed into a series of flat islands, one atomic layer in height, that are terminated with arsenic dimers. Also, B-type steps are preferred over A-type steps, causing the islands to exhibit narrow rectangular shapes with long straight edges. By contrast, when the surface is treated with tertiarybutylarsine in the CVD reactor, the initial coverage of arsenic is 2.0 ML. Upon annealing these samples in vacuum, the coverage remains constant up to 300°C, then slowly drops to zero as the temperature is raised to 600°C. At more than 1.5 ML of arsenic, the As:Ge (100) surface exhibits an unusual "waffle" pattern, with ridges about 20-50 Å in width crisscrossing the surface in the [110] and [-110] directions. Heating to 425°C, decreases the coverage to 1.0 ML. In this case, the surface is terminated with a series of square, flat islands that are separated by straight step edges one to three atomic layers in height. These surfaces are completely terminated with As dimers. Further heating to desorb the arsenic, causes the Ge (100) surface to transform back into a series of large terraces with their edges composed of equal amounts of A and B steps. The unusual morphology observed after exposure to tertiarybutylarsine in the CVD reactor is attributed to hydrogen-atom etching of the germanium surface.