Defect and Diffusion Forum Vols. 230-232

Abstract: Synchrotron white-beam x-ray topographs taken in the back-reflection mode have proved a powerful tool in the study of defects in semiconductor-grade silicon carbide crystals. Capable of mapping the distribution of axial dislocations across a wafer's area (notably the devastating micropipe defect), it can also provide information on their natures. Under favorable conditions, various other types of defect may be observed in back-reflection topographs of SiC, among which are subgrain boundaries, inclusions, and basal plane dislocations. Observed defect images in backreflection topographs may be simulated using relatively simple computer algorithms based on ray tracing. It has been possible to use back-reflection topographs of SiC substrates with device structures deposited upon them to relate the incidence of defects to device failure.

Abstract: In this chapter we present the results of the photoluminescent and optical investigations of the influence of cation vacancy-related defects on CdSe/ZnSe quantum dot organization. Selfassembling growth was achieved under molecular beam epitaxy with subsequent annealing step. Number of cation vacancies was controlled by the intensity of the emission band connected with complex that includes cation vacancy and shallow donor. For the first time it is shown that increase of number of cation vacancy related defects results in the reduction of potential fluctuations in the QD layer. In this case a relatively uniform dense array of QDs with shallow localization potential is organized. It is proposed that generation of cation vacancies during the growth suppresses both Cd segregation and Cd surface diffusion as well as facilitates Cd/Zn interdiffusion. Interdiffusion process is proved by the changes in the photoluminescence and optical reflection spectra of ZnSe layers. It is showned that Cd/Zn interdiffusion can play an important role in CdSe/ZnSe intermixing during the QD formation at least under such growth conditions which can stimulate generation of cation vacancies.

Abstract: A mechanism of g-induced (Co60 g-quanta of 1.25 MeV mean energy) changes in optical properties of ternary As-Ge-S chalcogenide vitreous semiconductors is analysed. It is connected with chemical bond re-switching accompanied by coordination topological defect formation. The origin of these defects for As-Ge-S system is discussed using data of positron annihilation lifetime spectroscopy, IR Fourier reflection measurements and mathematical statistics.

Abstract: We use DFT calculations to investigate the problem of hydrogen aggregation in silicon. We study atomic structures of finite hydrogen aggregates containing four or more hydrogen atoms. Beyond four hydrogen atoms, complexes consisting of Si-H bonds are likely to form, rather than aggregates of H2 molecules, which are the most stable diatomic hydrogen complex. Our calculations show that the basic structural unit of such complexes is a hydrogenated dislocation loop, which is formed spontaneously by a structural transformation of two H∗2 complexes. Hydrogen-induced formation of dislocation loops may account for the experimental observations of dislocation loops in proton-implanted or hydrogen plasma-treated silicon. We indicate the routes leading from H∗2 aggregates and hydrogenated dislocation loops to twodimensional hydrogen-induced platelets. We discuss the effect of hydrogen-catalysed formation of dislocation loops on the plasticity of silicon.

Abstract: Partially relaxed III–V heterostructures: GaAs/InGaAs and InP/InAlAs/InGaAs, with a small lattice mismatch, grown using molecular beam epitaxy under compressive or tensile misfit stress at the (001) interface, have been investigated by means of high-resolution X-ray diffractometry, atomic force microscopy and generalized ellipsometry. Additionally, transmission electron microscopy and electron-beam induced current in a scanning electron microscope have been employed to reveal misfit dislocations at the heterostructure interface. Chemical etching was used to determine polarity of the crystals and threading dislocation densities in the epitaxial layers. Our findings are interpreted in terms of the dependent on growth conditions, material’s composition and doping glide velocities of two types of misfit dislocations: α and β, differing in their core structure and lying along two orthogonal 〈110〉 crystallographic directions at the (001) interface.

Abstract: This paper describes the “pairing - dissociation” behaviour of metal-acceptor pairs and proposes a method to measure metal concentrations in p-type boron doped silicon based on a contactless measurement technique. The first part of this paper sums up the previous non destructive electrical characterization methods that have led to the evaluation of iron concentrations in p-type boron- doped silicon by the inspired contactless techniques. It is demonstrated that the lifetime measurement method proposed allows the detection of contaminants at concentrations as low as 109at.cm-3. In the second part, the specific cases of iron and chromium that are among the most harmful metal contaminants are discussed. We show that these contaminants, even if their concentrations are not known, are identifiable by contactless measurements that allow the analysis of their kinetics of pairing with boron atoms and of their respective interactions with extended defects, such as grain boundaries in multicrystalline silicon.