High spatial resolution and high-sensitivity techniques, such as DSL etching, AFM and TEM, have been used to analyse peculiar structural defects created in GaAs by Cu diffusion. They consist of (1) entangled grown-in dislocations surrounded by dislocation loops, (2) clusters of dislocation loops and (3) {001} complex planar defects revealed as square-like etch features on the (001) etch surface or as 〈100〉 linear etch features when these planar defects lie in the (100) or (010) planes perpendicular to the sample surface. The 〈100〉 linear defects are due to straight dislocation segments decorated by precipitates whereas the (001) defects are ascribed to loops from the clusters of type (2) that have selectively grown to a size much larger than the other ones. All these defects are surrounded by regions of enhanced etch rate. Their formation is ascribed to the interaction between point defects created during Cu diffusion that presumably occurs by the kick-out mechanism, whereby CuGa and Ga interstitials are formed.

The failure of high power InGaAlAs/AlGaAs double quantum well (DQW) lasers has been studied by plan-view photoluminescence (PL), cross sectional (002) dark field TEM and X-ray microanalysis. The lasers were operated at elevated driving currents beyond rollover in order to stimulate and analyse degradation processes encountered during accelerated lifetime testing. The damage consists of elliptical areas within which the original DQW structure was destroyed due to outdiffusion of Al into the confinement layers. The damaged areas started from the output mirror indicating that the device temperature was somewhat higher near the facet. The Ga vacancies governing the Al diffusion were likely produced by a mechanism of recombination enhanced defect reaction (REDR). The dislocations always present in the damaged areas are expected to be generated by the point defects produced by REDR as well as by localized thermal stresses.

The defects present after the diffusion of copper at 770 degreesC in semiinsulating LEC GaAs have been studied by TEM, photoetching and atomic force microscopy. Clusters of microloops in the matrix and around the dislocations have been observed. The enhanced etching velocity in the surroundings of the dislocations suggests that they have gettered Cu. The relationship between such defects and gettering and the generation of non-equilibrium point defects associated with Cu diffusion and incorporation in the GaAs lattice is discussed.

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.

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.