Search

A study was undertaken using the deep-level transient spectroscopy (DLTS) method in boron-doped high temperature/high pressure synthesized diamond (IIb) that explored the energy range 0.6 eV less than or equal to E-Ev less than or equal to 2.5 eV above the valence band. The method was being utilized to detect defect-related properties of silicon and gallium arsenide semiconductors. Results revealed that defects were discovered at 0.83 and 1.25 eV above the valence band edge.

Transmission and photothermal deflection spectroscopy were employed in examining the temperature dependence and optical constants of wurtzite AlxGa1-xN films prepared by plasma induced beam epitaxy. Interference fringes were used to determine the refractive index in the temperature range 7-295 K and photon energy range 1-5.5 eV. The refractive index was found to be a function of temperature, Al content and photon energy.

Electroluminescence and the transport characteristics of Wohler's siloxene are examined in either annealed or as-prepared states. Tests results indicate low dark conductivity due to room temperature and the intercalation of gas molecules between two polymer sheets. In addition, spectral and temperature dependences are found to affect the photoconductivity of the material.

Electron spin resonance (ESR) was found to be a useful and versatile method for the detection and characterization of preferred orientation effects in polycrystalline diamond films. The ESR signal coming from a nitrogen related center was composed of a central line and hyperfine satellite lines. Findings showed that crystallite disorientation induces a linewidth broadening of the satellite lines which can therefore be utilized to quantitatively characterize the diamond film texture.

Illumination-dependent current-voltage measurements and observations of electrically detected magnetic resonance (EDMR) were performed to investigate the transport mechanisms and degradation of green GaP:N light-emitting diodes. Specifically, a temperature-dependent isotropic EDMR signal was found to occur at low temperatures after degradation. Consequently, the EDMR was attributed to recombination processes near the p-n junction and correlated to degradation processes.

Metal-induced layer exchange (MILE) is a well-known method to grow large-grained high quality polycrystalline silicon on foreign substrates. We have modified the commonly used layer stack by an additional titanium interfacial layer (substrate/metal/titanium/oxide/amorphous silicon). The resulting layer exchange process is called titanium-assisted metal-induced layer exchange (Ti.MILE). For the investigated metals, Al (Ti.ALILE) and Ag (Ti.AgILE), the additional Ti layer does not affect the overall layer exchange process but results in a strong enlargement of the grains in the resulting polycrystalline silicon layer up to 250 μm. We have investigated the influence of the titanium interfacial layer on the process dynamics and grain growth. Furthermore, the structural and optical properties of the resulting polycrystalline silicon layer are investigated by means of different analysis methods. [ABSTRACT FROM AUTHOR]

Magnetotransport and atomic force microscopy research shows that AlGaAs antidot arrays produced by single-shot interference processing with a pulsed high-power Nd:YAG laser system are 3 by 3 millimeters in size. Elliptical or circular dot shapes with a diameter of between 255 and 690 nanometers are observed. Laser structuring has little affect on the two dimensional electron density although it significantly reduces mobility by a factor of 30.

In this work, the reverse aluminum-induced layer exchange (R-ALILE) process with an initial layer stack of substrate/amorphous Si/Si-oxide/Al was studied in detail. The influence of the annealing temperature on the sample properties was investigated by optical reflection/transmission measurements and Raman spectroscopy. In addition, focused ion beam measurements were conducted to elucidate the inner structure of the layers. Two steps during crystallization were observed: at first a substrate/Al-Si composite/closed poly-Si layer structure is formed with an activation energy EApoly-Si=1.1 eV, which can be transferred to the stable configuration of substrate/Al+Si-islands (hillocks)/poly-Si by extended annealing or a high temperature step (EAhillocks=2.4 eV). Both processes are basically independent at low annealing temperatures due to the large difference in activation energy. The transformation of the Al-Si composite to the Al/Si-hillock structure involves the crystallization of a-Si regions and their subsequent coalescence, different to the feedback mechanism suggested for the normal ALILE process, where hillock and closed poly-Si growth are believed to influence each other. This insight into the process leads to the possibility to prepare poly-Si layers on pure Al back contacts by R-ALILE, possibly improving efficiencies of solar cells prepared by epitaxial overgrowth of poly-Si seed layers. [ABSTRACT FROM AUTHOR]

The impact of Si impurities on the structural properties of AlN, grown by plasma-assisted molecular-beam epitaxy on c-plane sapphire is studied. Under nitrogen-rich growth conditions silicon can be homogeneously incorporated up to Si concentrations of [Si]=5.2×1021 cm-3. The presence of silicon on the surface during the growth process is demonstrated to be beneficial for the surface morphology and the structural properties of the AlN films. For [Si] up to (5±3)×1020 cm-3, this surfactant behavior results in a decrease of the surface roughness from 8 nm for undoped layers grown in a nitrogen-rich regime to less than 1 nm. In addition, high resolution x-ray diffraction studies reveal an increase of the average lateral crystal size from 300 nm to more than 1 μm and a simultaneous decrease of the screw dislocation density from 3.8×108 cm-2 for (comparably) weakly doped samples to 2×107 cm-2. At the same [Si] the heterogeneous stress shows a minimum of less than 50 MPa and drastically increases for higher [Si]. The analysis of edge dislocations as a function of [Si] reveals that their density is directly related to Si-induced compressive biaxial stress which increases up to (2.0±0.15) GPa, independently determined by x-ray diffraction and Raman spectroscopy. While edge dislocations are found to be strongly correlated with the release of stress, screw dislocations are formed due to the coalescence of AlN islands with different stacking order, as their density is decreasing with increasing lateral crystal size. For AlN films with [Si]<1.2×1021 cm-3, a Poisson ratio ν=0.525±0.022 is determined. [ABSTRACT FROM AUTHOR]

We present a model for the quantitative assessment of the influence of crystal defects on the piezoresistive properties of n-type cubic silicon carbide. In an extended carrier trapping model, the strain dependent transport at potential barriers formed by electrons in defect states at internal boundaries is calculated. Based on experimental results of electronic and structural characterization, the piezoresistive properties of nanocrystalline silicon carbide are derived. The magnitude of the piezoresistive gauge factor as well as its dependence on temperature, carrier density, and crystal orientation shows excellent agreement with the experimental findings. Taking the depth profile of the defect density into account, the same model is used to explain the depth dependence of the piezoresistive gauge factors in single crystalline cubic silicon carbide layers. [ABSTRACT FROM AUTHOR]

A detailed experimental study of the influence of crystal quality on the piezoresistive properties of n-type cubic silicon carbide grown by low temperature, low pressure chemical vapor depostion is presented. We have measured the longitudinal gauge factor in single-crystalline, polycrystalline, and nanocrystalline films as a function of conductivity and temperature as well as its directional dependence. In single-crystalline films, the piezoresistive gauge factor is strongly influenced by the layer thickness. The transition from single-crystalline to nanocrystalline 3C-SiC, achieved by a decrease in deposition temperature from 1200 to 1100°C, is shown to result in a change of the corresponding longitudinal piezoresistive gauge factor from -24.8 to positive values of +8 in nominally undoped films. In addition, we observe a drastic change in its dependence on conductivity. We attribute these results to the influence of crystal defects on the strain dependent conductivity. [ABSTRACT FROM AUTHOR]