Catalysis Reaction Kinetics of Photoactive Defects in Semiconductor

Uniformity and predictability are the principal qualities sought for all wet chemical etches. The establishment of these qualities, however, is hindered by a number of factom; such as nonuniformities in the starting material and random fluctuations in the local temperature and reactant concentration, which can lead to variations in etch rate across the surface of a wafer. The effects of variations in the local etch rate on the morphological development of an etching sutface and on the overall etch rate of the semiconductor are discussed. The system studied was an A1,,,Gao,6 As/GaAs heterostructure photodissolved in nitric acid using 730-nm laser light. Defects in the AlGaAs layer, which etched faster than the surrounding material, were responsible for variations in the etch rate. The defects also exhibited a degree of photosensitivity that has not been previously observed. It was also found that not all of the defects spanned the AlGaAs epilayer. A model for the overall etch rate was based on a system of noninteracting cylindrical defects with a distribution in depths.