Combination of selective etching and AFM imaging for the thickness analysis of AlGaAs/GaAs heterostructures

The vertical structure of AlGaAs/GaAs epitaxial layer systems for micro- and optoelectronic device fabrication has been studied by selective etching combined with AFM imaging. Dark etching and photoetching with CrO3-HF-H2O solutions were used to transform composition and doping variations into height differences of the cleaved (110) surface. The etching parameters (time, composition and supply of carriers by illumination) were optimized for accurate thickness determination by AFM. The measurements were corroborated by comparison with cross-sectional TEM mapping. The dependence of the etching rate on the composition and the occurence of small, but measurable height variations without any etching is discussed.