Laser-enhanced dissolution of gallium arsenide; aluminum gallium arsenide, and their heterostructures.

Abstract

The controlled, reproducible selective etching of semiconductors is imperative in the fabrication of solid state electronic devices. This work describes the laser-enhanced wet-chemical etching of heterostructures of n-type GaAs and AlGaAs using an expanded laser beam, which provides a nearly uniform light intensity over the entire sample surface. The results of this work show that the oxidation of arsenic by the capture of photo-generated holes is not first order, as is typically assumed, but rather follows a Langmuir isotherm. Models of the dissolution behavior of bulk and heterostructure materials are developed using this isotherm and the minority transport equation for the transport of holes from the bulk of the semiconductor to the surface assuming a uniform dissolution rate. However, the dissolution rate of AlGaAs may vary across the surface, even if illuminated by light with a photon energy less than the bandgap energy. Samples of AlGaAs demonstrated a localized, non-uniform etch rate at an applied bias of +0.5 V$\sb{\rm SCE}$ and under illumination by 730 nm light. This leads to a decreased selectivity for GaAs/AlGaAs heterostuctures and a complete failure of AlGaAs as an effective etch-stop layer. The effects of the heterogeneities were modeled using both a continuum model for non-interacting etch rate heterogeneities and a discrete model for interacting etch rate heterogeneities. A uniform etch rate can be recovered by eliminating the light source or lowering the applied bias.