SXS and XPS study of the adsorption and desorption of Te on GaAs (100)

Abstract

The adsorption and desorption of Te on GaAs 100 has been investigated using Soft X-ray Spectroscopy SXS and X-ray Photoelectron Spectroscopy XPS . The SXS measurements have been done at the Brazilian synchrotron facility LNLS, and the XPS study was performed using laboratory sources. The samples were MBE GaAs 100 layers covered in-situ by T e from an e usion cell. Two families of samples were studied: samples analyzed in-situ, and samples that were exposed to air for at least one week. The desorption of Te of the non-oxidized samples indicates that traces of Te remains in the surfaces for temperatures as high as 680 C. However, for the case of the oxidized samples, the Te lm sublimates easily at around of 250 C, leaving a clean GaAs surface. It seems that the oxidized Te lm works as a suitable protection for epitaxial GaAs layers.The study of adsorption and desorption of Te o n GaAs 100 is very important since Te can be used in the Surfactant Controlled Molecular Beam Epitaxy of InAs on GaAs 1 . In this work we i n vestigated the adsorption of Te on the surface of MBE grown GaAs 100 using an in-situ e usion cell for the deposition of Te. The evolution of the adsorption of Te w as monitored using in-situ XPS. The study of the desorption of Te was carried out in two di erent kind of samples, namely non-oxidized samples and samples exposed to air for at least one week. The non-oxidized samples were studied in-situ after the deposition of Te. The procedure used was to anneal the sample at a known temperature and to measure the XPS spectra, once the sample was at room temperature. RHEED experiments were carried out in this kind of sample, measuring the intensity o f di racted beams as a function of annealing temperature. The air-exposed samples were studied using the same procedure, but SXS experiments were carried out instead of RHEED.The integrated intensity o f T e as a function of the deposition time is shown in Fig.1. This process of adsorption of Te i s c haracterized by t wo di erent deposition rates. In the beginning the deposition rate is 0.16 A s or 0.043 ML s, considering that one monolayer of Te correspond to 3.72 A 2 . This rate is constant during the rst 6 A, but changes to 0.03 A s after 6 A o f Te. This change in the deposition rate of Te suggests a c hange in the sticking coe cient o f T e to the surface, at that critical thickness. The in-situ studied desorption of Te represented in Fig. 2a and 2b, show i n teresting results not yet fully understood. The RHEED intensity e v olution shows different structures, which m a y be related to the evaporation of successive l a yers of Te. The XPS measurements indicate that as the temperature increases rst