Materials Science Forum Vol. 725

Abstract: Anisotropies in misfit dislocations (MDs) at the interface of InGaAs/GaAs (001) are investigated by monochromatic X-ray topography (XRT) technique. Single MD line or several MD lines (MD bunching) are observed as white lines in XRT. Distribution, density, and number of MDs in one MD bunching are evaluated. The density of α-MDs is larger than that of β-MDs. Number of MDs in one MD bunching distribute with two peaks in both in-plane directions. In macroscopic view, α-MD bunching lay more orderly than the other. While in microscopic view, α-MDs gather for the range narrower than β-MDs.

Abstract: The effects of In incorporation on anisotropies in the strain relaxation mechanisms of InGaAs on GaAs systems are investigated using a three-dimensional reciprocal space mapping (3D-RSM) technique. Relaxation processes are classified as belonging to one of the following four phases: no relaxation, gradual relaxation, rapid relaxation, and relaxation saturation. Anisotropies appear in the gradual relaxation phase and almost disappear in the rapid relaxation phase. These anisotropies are enhanced by In content. When In content is low, both α- and β-misfit dislocations (MDs) are observed at the same thickness; the density of α-MDs increases more rapidly than that of β-MDs. When In content is high, only α-MDs appear in the gradual relaxation phase. These results suggest that In atoms prevent nucleation and/or gliding of β-MDs.

Abstract: The temperature dependences of the piezoelectric photo-thermal (PPT) signals from unintentionally doped p-type GaAsN films grown on semi-insulating GaAs substrate were measured from 80 to 300 K. From the theoretical analysis based on the rate equation for the recombination of photo exited carriers to the localized levels, we identified five majority hole traps, P1-P5 in GaAsN films. Among them, estimated concentrations of the P3 and P5 traps increased with the nitrogen contents. Therefore, we concluded that these two traps were due to nitrogen-related recombination centers in GaAsN.

Abstract: Ridge waveguides in InP-based heterostructures were fabricated by inductively coupled plasma (ICP) reactive ion etching using chlorine-based gases. The heterostructures included a series of 6 quantum wells (QW) made from quaternary material GaxIn1-xAsyP1-y emitting at 1.55 µm, and located very close to the surface (first QW at 250 nm). The etched structures (different widths and depths) were characterized at room and low temperature (80 K) by spectrum image cathodoluminescence (CL). The signature of the QWs was used to investigate effects induced by the dry etching process. Defects (or defect complexes) were observed, especially close to the edges of the etched structures, as well as a blue-shift of the CL lines from the nominal position. This was attributed to some intermixing of the QWs. Intermixing is induced by the defects that form during the dry etching process. The origin of these defects is discussed, taking into account previous studies performed on similar samples, except for the fact that the etched material was bulk InP instead of QW layers.

Abstract: A simple model is presented for the propagation of macroscopic defects within the quantum well (QW) plane of broad-area high power diode lasers. The catastrophic optical damage (COD) effect is considered the mechanism for creating an initial damage site and further development of defect pattern. The relations between the parameters used in the model and the actual physical properties of the semiconductor materials are discussed. Experimentally observed damage patterns are well described.

Abstract: The initial phase of defect propagation in broad area diode lasers, which are affected by the catastrophic optical damage (COD) effect, is studied. The decay of laser power within the first several 100 ns is found to be determined by defect propagation. When analyzing different device designs, a correlation is found between defect propagation velocities and thermal resistances of the materials vicinal to the quantum well, being the main heat source. The findings are confirmed by direct inspection of the defect pattern in opened devices.

Abstract: A new nondestructive method using terahertz waves for determining the carrier density of GaAs is proposed. The reflectance around the longitudinal optical (LO) phonon frequency changes with carrier density, whereas the reflectance around the transverse optical (TO) phonon frequency is constant. The relative reflectance, which is evaluated from the reflectance at the two frequencies related to the TO and LO phonon, as a function of the carrier density of GaAs was calculated from the dielectric function. A broadband tunable terahertz source is convenient for producing two waves around these phonon frequencies. Imaging of n-type GaAs wafer using this new terahertz method is described.

Abstract: In this contribution the basic principles of DLIT (dark lock-in thermography) are introduced and typical application examples are shown. These results are compared with that of other solar cell characterization techniques like electroluminescence (EL) and photoluminescence (PL) imaging, which are also very popular in Germany. It will be shown that these techniques are largely complementary to each other. Luminescence techniques are most sensitive for the detection of local recombination centers in the bulk and of series resistance problems of the cells, whereas DLIT is most effective for investigating all problems being connected with the dark current of the cells. A new DLIT technique is introduced which allows a separate imaging of the so-called diffusion current and the recombination current. These two contributions of the dark current are based on different physical mechanisms (recombination in the bulk and in the depletion region, respectively), and their spatial distributions differ significantly. Such investigations are impossible by applying luminescence-based imaging techniques.

Abstract: Removed due to authors request.

Abstract: Interactions between intra-grain defects and metal impurities in multicrystalline silicon (mc-Si) were evaluated. After metal contaminations, EBIC contrasts at > 1.5o SA-GBs were more enhanced than those at Ni/1000 oC > Ni/600 oC. These results might attribute to Fe atoms form deeper energy levels of recombination centers than Ni atoms and the gettering abilities at SA-GBs depend on the misorientation angles. Many dark spots were observed in EBIC images in the Ni/600 oC. Since the dark spots corresponded to the etch pits, the dark spots might be dislocations decorated with Ni. The gettering abilities of SA-GBs depended on the misorientaion angles, and the recombination properties at SA-GBs and dark spots, such as small defects after metal contamination were different by annealing temperatures and the types of metal impurities.