Al x Ga 1−x As native-oxide-based distributed Bragg reflectors for vertical cavity surface emitting lasers

Abstract

The problems associated with constructing AlxGa1−xAs native-oxide-based distributed Bragg reflectors (DBRs) for vertical cavity surface emitting lasers are investigated. Reflection and stability measurements are performed on structures with central λ/2 cavities (λ∼980 nm) of GaAs surrounded by two periods of native-oxide-based DBRs on the top and 2.5 periods on the bottom. Prior to crystal oxidation (H2O vapor+N2, 430 °C) a period of the DBRs consists of a ∼λ/4 optically thick layer of GaAs and a thicker (oxidation) layer of AlxGa1−xAs (x=0.95, 0.96, 0.97, 0.98, 1.00) surrounded by thinner (∼100 Å) buffer layers that are AlyGa1−yAs (y=0, 0.25, 0.50, 0.65, 0.070, 0.75, 0.80, 0.85). The DBRs are formed after oxidation of the high Al composition AlxGa1−xAs layers, and to some extent the AlyGa1−yAs buffer layers, forming a ∼λ/4 optically thick layer of the native oxide. For comparison, more complicated DBRs are created by oxidizing superlattice layers. It is found that the AlxGa1−xAs composition, x, of the oxidation layer, choice of oxidizing or nonoxidizing AlyGa1−yAs buffer layers (y), oxidation parameters, and post-processing parameters determine the DBR quality and stability, as well as the possibility of reoxidation.