Effects of geometry on the wet thermal oxidation of aluminum arsenide

Citation

Alonzo, Alicia Cristina (1999) Effects of geometry on the wet thermal oxidation of aluminum arsenide. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Q286-WB43. https://resolver.caltech.edu/CaltechETD:etd-02082008-165325

Abstract

In recent years, the wet thermal oxidation of high aluminum-content III-V semiconductors has provided significant device improvements, most notably in vertical cavity surface emitting lasers (VCSELs). Although circles and squares are the most efficient geometries for VCSELs, most studies of the oxidation process to date have been conducted exclusively with stripes, rather than these two-dimensional mesa structures. The studies presented in this thesis examine the effect of geometry on the wet thermal oxidation process, focusing primarily on those mesa geometries with direct applicability to VCSELs. However, many of the results can be applied to more exotic mesa shapes as well.

A model is presented for the time-dependence of oxide formation in two-dimensional mesa structures. This work represents the first attempt to model the oxidation of square mesas. Although other researchers have recently proposed models for the oxidation of circular mesas, these models do not adequately account for the effect of geometry on the oxidation process. As compared to the one-dimensional oxidation of stripes, the oxidation of circular and square mesas exhibits an increased oxidation rate as the process proceeds. This is a direct effect of the geometry of the mesas. Extensive data is presented in support of our model, and a comparison is made to other models for the oxidation of circular mesas.

The two-dimensional mesa geometry, coupled with anisotropies in the oxidation process itself, is shown to produce variations in the strain induced in the overlying GaAs layer by the oxidation process. Using micro-Raman spectroscopy, this strain has been spatially mapped and shown to correspond to color variations observed in the mesas with an optical microscope. A crystallographic-dependence for the oxidation is documented and used to explain the spatial variations in the strain as well as the shape of apertures formed in circular and square mesas by the wet thermal oxidation process.

Thesis Files