Laser-stimulated structural transformations in AlxGa1-xAs/GaAs system

Abstract

Structural changes in the AlxGa1-xAs thin films doped by Zn atoms on the semi-insulating GaAs substrate under irradiation by laser pulses (λ = 0.532 μm, τp = 10 ns) were investigated. The analysis of photoluminescence (PL), Raman spectroscopy and atomic force microscopy (AFM) of AlxGa1-xAs surface showed that the long-wave shift of the PL band maximum (E = 1.82 eV) induced by pulsed laser (λ = 0,532 μm, τp = 10 ns) is caused by the redistribution of Al atoms in solid phase toward the AlxGa1-xAs film surface due to a laser thermal shock (LTS) effect. As a result the surface concentration of the Al atoms increases. Contrary, the integral number of the Al atoms decreases due to their partial sublimation from a free surface. The increase of PL band intensity is caused by an increase of the concentration of Zn atoms, which fill the vacancies of the aluminum atoms (VAl) created as a result of the LTS effect action. The movement of the A1 atoms in the solid phase caused by the high values of the temperature and pressure gradients which is consistent with the results of theoretical calculations. As a result, the AlxGa1-xAs film is depleted by Al atoms. When laser intensity reached the melting threshold and beyond, the following re-crystallization of the near surface layer results in 3D topographical changes on the AlxGa1-xAs film surface. This surface layer topography is formed as nano-islands with an average lateral dimension of ~ 80 nm.