Progress in the layer thickness determination of AlGaAs/GaAs heterostructures using selective etching and AFM imaging of the (110) cleavage planes

The cross-section of Ga(Al,In)As/GaAs heterostructures has been investigated by selective wet etching using citric acid/hydrogen peroxide (C6H8O7:H2O2), NaOCl, HCl and diluted CrO3-HF solutions. Composition and doping variation were transformed to height differences of the cleaved surface and measured by atomic force microscopy (AFM). The etchants were optimized for various heterostructure layer systems and compared with respect to selectivity and suitability for the investigation of layer thicknesses of AlGaAs/GaAs and InGaAs/GaAs heterostructures. We have demonstrated the possibility to reveal superlattices and quantum wells down to a thickness of 7 nm, and to distinguish between layers of the same composition but different doping type.