Phase transitions in compound semiconductor films triggered by laser irradiation

Abstract

The preparation of AlSb thin films by pulsed laser annealing of Al-Sb sandwiches is studied in order to resolve some past uncertainty about the temperature rise induced by the laser pulse. Using 1000-Å-thick 2-layer films supported by transmission electron microscope grids, we investigate the energy threshold for transformation as a function of pulse duration (from 15 ns to 100 ms) and of ambient temperature up to ∼600 K. We thence calculate the temperature effect directly induced by the laser to be ∼930 K, whereas inert gas furnace anneals of identical films show transformation at this temperature occurring only in times ≳100 sec. We discuss the isoenergetic nature of the system for short-laser pulses and the role of the heat of formation, and propose a model which is then shown to work equally well for the systems CdTe, CdSe, and AlAs. We conclude that the reaction is thermally triggered by the laser pulse, but is to some extent self- sustaining via the heat of formation locally distributed.