Structure-induced effects on the selective wet thermal oxidation of digital AlxGa1–xAs alloys

Abstract

A thorough study of the selective wet oxidation in digital AlxGa1–xAs alloys is presented. We report experimental results and physical interpretation on the oxidation kinetics within those ranges of the AlGaAs composition (x = 0.95 to 1) and layer thickness (20 to 50 nm) of interest for oxide-aperture vertical-cavity surface-emitting laser (VCSEL) application. We demonstrate the high controllability of the oxidation reaction between different Al compositions; made different thanks to the use of digital alloys. Unlike standard alloys, we measured an invariability of the oxidation rates in the studied thickness range (20–50 nm), implying a better control of the fabrication process. The dependence of the reaction rate with the temperature is expressed as an Arrhenius law. Two activation energies (1.2 and 0.55 eV) have been derived for composition ranges of x = 0.95–0.98 and x = 0.99–1, respectively, revealing that two different mechanisms are involved depending on the Al content and the superlattice structure of the digitally-grown AlGaAs.