Crystallization Process and Chemical Disorder in Flash Evaporated Amorphous Gallium Antimonide Films
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**UNESP, FC, Depto. de Fisica. CEP 17033-060, Bauru, SP, Brazil, and also Universidade Estadual de Campinas, Instituto de Fisica. 13081-970. Campinas, SP, Brazil.
ABSTRACT
In this work we describe a flash evaporation system specially built to characterize and produce amorphous films of III-V compounds GaSb films using optical, electrical and X-Ray diffraction measurements. Changes in the composition of the GaSb samples were obtained by the use of different crucible temperatures. In such samples, consequently, the optical absorption edge and the DC electrical conductivity were modified. The departure from stoichiometry in GaSb films is analyzed on the basis of these results which can be used as an evidence of the chemical disorder. This kind of disorder is represented by either wrong bonds or sites with different coordination. Thermal annealing with a sequence of increasing temperatures first induced detectable variations in the optical absorption edge and in the vibrational properties of the amorphous GaSb. These variations are compatible with the GaSb local ordering and were observed by Raman scattering and infrared absorption spectra. The annealing at higher temperatures allowed the crystallization of the material confirmed by X-Ray diffraction. From these experimental results a crystallization mechanism based on the segregation of Sb excess coming from the crystallized regions toward the amorphous tissue is proposed. INTRODUCTION
In the crystallization of bulk GaSb from the melt, when the thermodynamic equilibrium is practically attained, there is a strong tendency to the formation of stoichiometric material'. Differently, stoichiometry in amorphous GaSb films prepared by evaporation is a difficult task 2' 3' 4. Even if the amorphous material is stoichiometric some degree of chemical disorder is present besides the structural disorder. The combined effects of these two kinds of disorder on the physical properties of the materials are not well understood at present. In this work we describe some experiments related to the chemical and structural disorder in the amorphous semiconductor GaSb, and the results are used to qualitatively check some recently developed models-" . EXPERIMENTAL PROCEDURE
A set of a-Ga -xSbx films with different concentrations (0.50_sx_
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