Thermal desorption of amorphous arsenic caps from GaAs(100) monitored by reflection anisotropy spectroscopy

• Published in: Applied surface science 1993, Vol.63 (1), p.106-110
• Main Authors: Resch, U., Scholz, S.M., Rossow, U., Müller, A.B., Richter, W., Förster, A.
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Solid-gas interface; Surface physical chemistry
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/0169-4332(93)90072-J

Arsenic layers were deposited on top of molecular beam epitaxy (MBE) grown GaAs(100) layers by cooling the samples after growth in an As 4 flux down to temperatures of about - 5°C. Raman scattering has shown that these arsenic layers are adsorbed in on amorphous structure (Surf. Sci. 269/270 (1992) 797). Consequently, the As overlayers, the so called As-“caps”, show no anisotropy in reflectivity, which means that no reflection anisotropy spectroscopy (RAS) signal is detected from the caps. After storage in air for several weeks desorption experiments were performed in ultra-high vacuum (UHV) in order to recover the GaAs(100) surface. The samples were heated stepwise to temperatures of at least 545°C. After desorption of most of the As layer a first RAS signal can be detected. From this stage on the RAS spectra undergo strong variations with increasing annealing temperature. This is correlated with a decreasing As content of the GaAs surfaces, as revealed by means of Auger electron spectroscopy (AES) and also with LEED patterns of different symmetries. The RAS spectra, however, turn out to be much more sensitive than the observable changes in the symmetry of the LEED pattern. RAS is therefore suitable to monitor not only the decapping procedure but, once calibrated, also allows for a fine tuning of the As/Ga ratio at the surface.