A. Guillén-Cervantes, Z. Rivera-Alvarez, M. López-López,

E. López-Luna, and I. Hernández-Calderón

Physics Department, Centro de Investigación y Estudios Avanzados del IPN

Apartado Postal 14-740, México 07000 D.F., México.

Based on results of atomic force microscopy (AFM), Auger electron spectroscopy (AES) and reflection of high energy electron diffraction (RHEED) a model intended to explain the thermal desorption mechanism of the GaAs surface oxides is proposed. According to this model GaAs surface pits observed by AFM on thermally cleaned samples in ultra high vacuum (UHV) are closely related to the desorption of unstable As-oxides at temperatures as low as ~ 350° C. By the other hand the most stable Ga-oxides can only be removed at temperatures in the order of 540° C. During the thermal cleaning process, at temperatures of ~ 350° C unstable As-oxides are first evaporated leaving areas covered by the most stable Ga-oxides in the vicinity of bare GaAs regions. When temperature increases up to ~ 500° C the Ga-oxides are evaporated by reacting with the elements of the substrates in chemical reactions that promote the generation of surface pits. In order to improve the GaAs surface morphology we tried the thermal oxide desorption assisted by an H radical flux. We found that surface pits can be avoided employing this process.

This work was partially supported by CONACyT.