Structure-induced effects on the selective wet thermal oxidation of digital Al_xGa_1–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.

Optimal control of AlAs oxidation via digital alloy heterostructure compositions

“…• The first sample (A) is a bulk alloy of 50 nm thick AlAs surrounded by 100 nm GaAs. • The second sample (B) is similar to the one studied in [9], but in this structure only a total thickness of 70 nm is considered. The SL consists of a (0.…”

“…Recently we reported on the oxidation in a (0.6 nm Al 0.7 Ga 0.3 As)/(n 2 nm AlAs) SL for n 2 varying between 3 and 8 nm [9]. The conclusion was that the oxidation is carried out mainly for the AlAs unit layers of the DAs, but the exact effect of the thin barriers was not clearly established.…”

“…Nevertheless, using epitaxial techniques such as molecular beam epitaxy (MBE), AlAs/Al x Ga 1−x As superlattice (SL) structures (also called digital alloys (DAs)) can also be used to achieve a given composition. Indeed, the oxidation of DAs exhibits some advantages compared with bulk alloys, such as easier control of the alloy composition [9] or better mechanical properties [10], allowing a finer tuning of the oxidation depth.…”

Impact of an Antiresonant Oxide Island on the Lasing of Lateral Modes in VCSELs

“…Oxidation follows through the holes and spreads inside the AlGaAs layer. The speed of oxidation depends both on the amount of Al in the material and on the thickness of the layer [39]. After the process of oxidation, the next phase of epitaxial growth can be performed and a stack of layers can be grown above the oxidized material.…”

Improvement of the oxidation interface in an AlGaAs/AlxOy waveguide structure by using a GaAs/AlAs superlattice

“…The intrinsic strain induced by oxidation volume shrinkage was also studied by micro‐photoluminescence . AlAs/Al x Ga 1 − x As superlattice (SL) can also be used instead of uniform AlGaAs layers in order to achieve an easy control of the alloy composition and a precise tuning of the oxidation depth . After oxidation, better mechanical properties were obtained .…”