Effects of Electron Beam Exposure Conditions on the Surface Modification of CaF2(111) for Heteroepitaxy of GaAs/CaF2Structure

Autor: Hwang, Sang-Man, Miyasato, Keiichiro, Koji Kawasaki, Koji Kawasaki, Kazuo Tsutsui, Kazuo Tsutsui
Zdroj: Japanese Journal of Applied Physics; March 1996, Vol. 35 Issue: 3 p1701-1701, 1p
Abstrakt: Optimal conditions of electron beam exposure for the surface modification of CaF2(111) by simultaneous exposure of an electron beam and an As4molecular beam were studied for the purpose of obtaining good electrical properties of heteroepitaxial GaAs films grown on modified CaF2. The amount of adsorbed As atoms on the CaF2surface and the crystallinity of grown GaAs film evaluated from electron mobility and cross-sectional transmission electron microscopy were examined by changing the electron energy (VE) and dose (DE). It was found that with adsorption of 1 atomic monolayer of As on the modified CaF2surface, the highest mobility of electrons and low defect density in the GaAs films were obtained when the value of VE×DEwas a constant of about 300 mJ/cm2in the range of 40 eV?VE?300 eV. These results indicate that the degree of surface modification is governed by the total energy of incident electrons per unit area rather than VEor DEindividually. In addition, a deviation from this relationship was observed at VEof 20 eV and 3,000 eV. Possible models for this constant VE×DErule are proposed, in which F vacancies or secondary electrons generated in the bulk CaF2propagate to the surface of CaF2to provide occupation sites of As atoms.
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