Solid State Phenomena Vols. 131-133

Abstract: The studies of electrical activity of deep electron traps and the optical response of partially-strain relaxed InxGa1-xAs layers (x=5.5%, 7.7% and 8.6%) grown by metalorganic vapourphase epitaxy (MOVPE) have been performed by means of deep-level transient spectroscopy (DLTS) and photoreflectance (PR). DLTS measurements revealed two electron traps. One of the trap has been attributed to electron states at α-type misfit dislocations. The other trap has been ascribed to the EL2 point defect. The PR spectra at room temperature were measured and analysed. By applying the results of theoretical calculations which include excitonic and strain effects, we were able to estimate the extent of strain relaxation and the values of residual strain in the partially relaxed epitaxial layers.

Abstract: We have carried out DLTS in highly doped p+n Ultra Shallow Junctions (USJ) in Si formed by ion implantation. The samples were implanted either with a 10keV or a 5keV B implant at a dose of 5*1015cm15. The 10keV sample was also implanted with P and the 5keV samples were implanted with P and increasing doses of As to simulate an USJ in an n-well. Due to the high P and/or As implant doses, it was observed that a band offset also exists between the n-type implanted region and the n-type starting material. Therefore these samples contain another depletion region apart from the expected p+n depletion region. However, the electric fields in these regions act in opposite directions assisting the profiling of different regions after careful selection of biasing conditions. A deep state is observed in the n-type region at EC-0.34eV which has a complex Laplace DLTS signature, which has arisen due to the implantation process.

Abstract: Regular dislocation networks formed as a result of the direct bonding of Cz-Si wafers with oxide remnants on the pre-bonding surfaces were investigated. Besides the dislocation network, oxide precipitates were detected at the bonding interface. The precipitate density across the network was ~5×1010 cm-2, except small irregularly distributed circular areas, several mm in diameter, where the density was remarkably lower (<5×108 cm-2). The dislocation network structure was not affected by the change in the precipitate density. Photoluminescence spectroscopy (PL) and light beam induced current (LBIC) mapping were applied for characterization of such dislocation networks. For the locations with high precipitate density, PL signal from dislocations and that from the band-to-band transitions were enhanced. On the other hand, the LBIC results indicated that oxide precipitates are active recombination centers and thus should suppress the observed radiative transitions. The controversy can be explained in the assumption that the D-band PL signal increases due to scattering of excitation light by the precipitates and due to related expansion of the excitation area of the dislocation network. The light reflection from the precipitate layer also enhances the detected band-to-band PL signal. The shape of PL spectra from the samples in the range of photon energies 0.75 – 1.15 eV was not influenced by the oxide precipitates.

Abstract: With an innovative measurement technique termed “microwave detected photoconductivity” (MDP) it is possible to investigate defects of silicon wafers contact less and topographically by evaluating photoconductivity transients detected via microwave absorption. Thus it is possible to obtain the electrical key parameters (e.g. diffusion length and lifetime) in a contact less, non destructive and topographic way. The method is ideal for the investigation of process induced defects as a function of different processing steps. The inhomogeneities of the diffusion length map of the pure wafer correlate very well with the key parameter map of photosensor devices. Even more details of process induced failures of devices can be detected in detail with MDP. In general, the measurement conditions together with their evaluation can be tuned to nearly ‘predict’ properties and production yield of final devices for a given chain of processing steps.

Abstract: In this work, a methodology, based on a self-organization process, to form gold nanoclusters on the 6H-SiC surface, is illustrated. By scanning electron microscopy and atomic force microscopy the gold self-organization induced by annealing processes was studied and modelled by classical limited surface diffusion ripening theories. These studies allowed us to fabricate Au nanoclusres/SiC nanostructured materials with tunable structural properties. The local electrical properties of such a nanostructured material were probed, by conductive atomic force microscopy collecting high statistics of I-V curves. The main observed result was the Schottky barrier height (SBH) dependence on the cluster size. This behaviour is interpreted considering the physics of few electron quantum dots merged with the ballistic transport. A quite satisfying agreement between the theoretical forecast behaviour and the experimental data has been found.

Abstract: Microstructural analysis of power devices were carried out on components from Freescale Semiconductor that underwent extreme electro-thermal fatigue. Several destructive and non destructive techniques were used. It is shown that the main cause of devices failure is delamination between the heat sink and the power die. Additional causes of failure are identified. The fatigue-induced modifications of the structure of the metallization layer (grain growth, grain boundary grooving) is also discussed.

Abstract: Calculation of relation between the EBIC contrast and the recombination strength for dislocations and quasi-two-dimensional dislocation trails has been carried out taking into account the real values of depletion region width. Using the relations obtained the linear defect density along dislocations and sheet density in dislocation trails are estimated. The results of EBIC investigations of dislocations and dislocation trails in plastically deformed n- and p-Si are analyzed.

Abstract: The generation of semiconductor nanowires (NWs) by a “bottom-up” approach is of technological interest for the development of new nanodevices. In most cases Si and SiGe nanowires (NWs) are grown by molecular beam epitaxy (MBE) and by chemical vapor deposition (CVD) on the base of the vapor-liquid-solid-mechanism (VLS). In both cases small metal droplets act as a seed for the NW formation. The article mainly refers to the specific features of the MBE growth. The application of metals related to the VLS growth concept (quite often gold droplets are used) also causes several disadvantages of this approach, e.g., the formation of a metal wetting layer on all surfaces, dislocations, and electric active point defects. Concerning the formation of devices, technological steps, such as oxidation and doping of NWs, have to be considered. Specific techniques have to be applied to investigate the properties of individual semiconductor NWs. Some examples shall illustrate this topic.

Abstract: Samples with layer of silicon nanocrystals embedded in SiO2 (the single phase Si content in oxide ranged between 5 and 92 volume %) were subjected to high energy ion implantation. Implantation-induced modifications of SiO2-ncSi properties discussed in this paper include a shift of the major ncSi-related photoluminescence peak and intensification of the high-photon energy peaks, that accompany the change in amount and type of the charge trapped on the nanocrystals. A unified model is suggested for all these phenomena.