Effect of film thickness and laser energy density on the microstructure of a-GaAs films after excimer laser crystallization

Abstract

A KrF excimer laser with 30 ns pulse duration is used for crystallization of a-GaAs grown on silicon substrate using molecular beam epitaxy technique. The effect of laser energy density and film thickness on grain morphology has been studied. Scanning electron microscopy and high-resolution electron backscatter diffraction have been used to study the texture and microstructure evolution during the crystallization of initially amorphous GaAs thin films. The integrated information on grain size distribution, preferred orientation, and nature of grain boundaries provides useful information to postulate the mechanism of grain growth and the likely role of different contributing parameters in the evolution of final texture under the highly transient processing conditions prevailing during the short laser irradiation. The texture ranges from weak ⟨111⟩ fiber texture to strong ⟨100⟩ texture depending on film thickness and laser influence. The grain structure and texture development are discussed based on the three melting regimes: (1) partial meting regime; (2) complete melting regime; and (3) near-complete melting regime.