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Heteroepitaxial AlN films grown on (100)- and (111)-oriented diamond (Cα) substrates by plasma-induced molecular beam epitaxy have been investigated by x-ray diffraction (XRD) and atomic force microscopy (AFM). High quality epitaxial growth of almost strain-free wurtzite AlN is observed for both orientations. For the AlN/Cα(111) heterostructures, the epitaxial orientation relationship (0001)[1010] AlN∥(111)[011] Cα is obtained. However, a significant fraction of up to 20% of the epitaxial layer is oriented differently with (1011) AlN∥(111) Cα. In case of AlN on Cα(100), a double-domain structure with either (0001)[1010] AlNI∥(100)[011] Cα or (0001)[1210] AlNII∥(100)[011] Cα is found. The linewidths of the XRD ω and 2θ/ω scans of the symmetric AlN 002 reflection have been determined as 1.4 and 0.17° for AlN/Cα(100), 0.55° and 0.11° for AlN/Cα(111), as well as 0.51 and 0.05° for an AlN/sapphire (0001) reference sample grown under similar conditions. Thus, the crystal quality of AlN on Cα(111) is close to that of AlN on sapphire. The corresponding AlN rms roughness values found by AFM are 1.9 nm on Cα(100), 1.7 nm on Cα(111), and 3.2 nm on sapphire (0001), respectively. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We analyze the influence of crystal quality on the electronic properties of 3C-SiC layers deposited by low-pressure chemical vapor deposition. Single crystalline films show good electronic quality and can be efficiently doped with NH3. The transition to nanocrystalline 3C-SiC, achieved by a decrease in deposition temperature from 1200 °C to 1100 °C, results in a decrease of the carrier mobility and an increase of the residual carrier concentration in nominally undoped layers. Comparative analysis by scanning electron microscopy, transmission electron microscopy, and secondary ion mass spectroscopy reveals an enhancement of the average oxygen concentration by almost two orders of magnitude and an accumulation of oxygen at crystal defects. The density and distribution of oxygen decorated defects are shown to be responsible for the increasing density of residual carriers in polycrystalline and nanocrystalline films. In single-crystalline films, the depth distribution of such defects explains the dependence of residual carrier density and mobility on the layer thickness. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Cathodoluminescence (CL) in the scanning electron microscope and atomic force microscopy (AFM) have been used to study the formation of pinholes in tensile and compressively strained AIlnGaN films grown on Al 2 O 3 substrates by plasma-induced molecular beam epitaxy. Nanotubes, pits, and V-shaped pinholes are observed in a tensile strained sample. CL images show an enhanced emission around the pits and a lower intensity at the V-shaped pinholes. Rounded pinholes appear in compressively strained samples in island-like regions with higher In concentration. The grain structure near the pinholes is resolved by AFM. [ABSTRACT FROM AUTHOR]

Alkene molecules were covalently bonded to hydrogen-terminated crystalline silicon (111) and hydrogenated amorphous silicon (a-Si:H) surfaces by thermally induced hydrosilylation. The resulting chemical surface structure was analyzed by x-ray photoelectron spectroscopy and compared to that of the corresponding silicon surfaces covered by a native oxide and terminated with hydrogen. Our results demonstrate successful hydrosilylation on both substrate materials. However, the presence of oxygen on the surface turns out to hinder the hydrosilylation reaction, as shown by the reduced concentration of hydrocarbons on the surface after prolonged exposure of the Si substrates prior to hydrosilylation. By monitoring both the O 1s and the Si 2p peaks, the oxidation kinetics of a-Si:H was found to be diffusion limited. Since stable hydrogen termination as a prerequisite of hydrosilylation can be achieved on a-Si:H surfaces with much less technological effort than on crystalline silicon surfaces, a-Si:H is a promising substrate for biofunctionalization procedures requiring less stringent process conditions. [ABSTRACT FROM AUTHOR]

The oxidation states of Mn in epitaxial GaN films grown by plasma induced molecular beam epitaxy were investigated by electron spin resonance (ESR), elastic recoil detection, superconducting quantum interference device magnetization, and photothermal deflection spectroscopy measurements. Comparison of the measured Mn[SUP2+] spin densities with the total Mn concentrations in GaN of about 10[SUP20]cm[SUP-3] indicates that the majority of Mn is present in the neutral Mn[SUP3+] acceptor state. In samples codoped with Si, electrons are transferred to the Mn acceptors, which is observed by a strong increase of the Mn[SUP2+] spin densities in ESR. Simultaneously, this charge transfer reduces the characteristic optical absorption features at 1.5 and above 1.8 eV, suggesting their assignment to a Mn[SUP3+]-related gap state. [ABSTRACT FROM AUTHOR]

Polycrystalline silicon layers are prepared by interference laser crystallization (ILC) in the superlateral growth regime. To characterize their microscopic photoelectrical properties, light beam induced current (LBIC) is used, employing a focused laser beam for local generation of photocarriers in the layers with spatial resolution of ≈0.4 µm. The results are correlated with surface morphology obtained by atomic force microscopy. In the single pulse ILC, the temperature profiles are optimized by changing the proportion of interfering beam intensities. The typical grains are of triangular shape, with a length of 1.5 µm and width <0.5 µm. The photocurrent response is dominated by variations in the sample thickness. In the multiple pulse ILC, thin films with grains of quadratic shape and of size exceeding 5 µm are obtained by shifting the sample through an interference pattern, thus taking advantage of lateral epitaxial regrowth. Here, by use of a lock-in, LBIC can detect position and local electronic properties of individual grain boundaries. Grain boundaries are clearly identified by 180° shifts of the photocurrent phase close to maxima of photocurrent amplitude. The photocurrent is attributed to local fields at grain boundaries. These fields extend about 1.4 µm into the grains. The barrier height at the boundary is about 110 mV. [ABSTRACT FROM AUTHOR]

High-resolution photoluminescence spectra have been measured in high-quality homoepitaxial GaN grown on a free-standing GaN substrate with lower residual strain than in previous work. Unusually strong and well-resolved excitonic lines were observed. Based on free- and bound exciton transitions some important GaN parameters are derived. The Arrhenius plot of the free A exciton recombination yields a binding energy of 24.7 meV. Based on this datum, an accurate value for the band-gap energy, E[sub G](4.3 K) = 3.506 eV, can be given. From the donor bound excitons and their “two-electron” satellites, the exciton localization energy and donor ionization energy are deduced. Finally, estimates of the electron and hole masses have been obtained within the effective mass approximation. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ga-face AlGaN/GaN heterostructures with different sheet carrier concentrations have been studied by photoluminescence and Raman spectroscopy. Compared to bulk GaN, an energy shift of the excitonic emission lines towards higher energies was observed, indicating the presence of residual compressive strain in the GaN layer. This strain was confirmed by the shift of the E[sub 2] Raman line, from which biaxial compressive stresses ranging between 0.34 and 1.7 GPa were deduced. The spontaneous and piezoelectric polarizations for each layer of the heterostructures have been also calculated. The analysis of these quantities clarified the influence of the residual stress on the sheet electron concentration (n[sub s]). Possible causes for the discrepancies between the calculated and experimentally determined sheet carrier densities are briefly discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The piezoresistivity of wurtzite Al[sub x]Ga[sub 1-x]N layers with different Al contents and electron concentrations grown by plasma induced molecular beam epitaxy is investigated. A strong increase of the piezoresistivity with increasing Al content and decreasing carrier density is observed. The corresponding piezoresistive gauge factor is negative and its absolute value increases from 3.5 to 25.8 if the Al concentration is increased from x=0 to 0.35. The dependence of the piezoresistive effect on the free electron concentration in the epitaxial layers is calculated by a model which compares the strain induced piezoelectric field to an externally applied gate voltage in field effect transistors. In addition, the strain dependence of the channel conductivity in pseudomorphic, undoped AlGaN/GaN high electron mobility transistors containing a polarization induced two-dimensional electron gas close to the heterointerface, is measured. A remarkably high gauge factor of -85 is observed for these devices. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Long living excited states in boron doped diamond are detected by photoconductivity and photoconductivity excitation spectroscopy at temperatures T<190 K in the energy regime 3.2-3.5 eV. The photoconductivity spectra show pronounced maxima in highly doped [(4-8)x10[sup 18] cm[sup -3]] diamond which decrease with decreasing doping density. A model is presented where holes are optically excited from compensating deep defects, 3.36 eV above the valence band edge, into the valence band. Here they get captured by LO phonon emission into long living excited levels of boron. The long living excited states are 200, 240, and 266 meV above the 1s ground level. Maxima in photocurrent can be detected at high doping concentrations as the wave function overlap between neighboring excited states is significant to allow hopping transitions between neighboring excited states. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents the results of scanning electron microscopy, micro-Raman spectroscopy and photoluminescence measurements on magnesium-doped GaN films grown by metalorganic chemical vapor phase deposition. Surface morphology; Optical characterization; Excitation photon energy dependence; Temperature dependence.

Studies the influence of the nitrogen nuclear spin on the optically detected magnetic resonance and electron spin resonance signatures of the intrinsic shallow donor and a deep defect causing the characteristic yellow luminescence on wurtzite GaN epitaxial layers grown by plasma induced molecular beam epitaxy. Electron spin resonance of the effective-mass donor.

Analyzes the amplitude of interference fringes in optical absorption spectra for thin films in the range of low absorption coefficients. Experimental details; Light intensity profiles in thin films; Simulation of the interference fringes; Information on substrate and film edge absorptions.

Reports on the structural and electronic properties of hydrogenated amorphous silicon-germanium alloys deposited by radio frequency glow discharge from SiH[sub4] and GeH[sub4] in a diode reactor. Samples used in the study; Information on deposition conditions and alloy composition; Hydrogen bonding.

Investigates the vibrational, electrical and optical properties of hydrogenated amorphous silicon-selenium alloys. Preparation of the alloy thin films; Details of the infrared and Raman spectroscopy; Dark conductivity and photoconductivity.

Presents a study which investigated the diffusion of hydrogen into InAs deposited on semi-insulating gallium arsenide substrate and compared the properties of the layers before and after hydrogenation. Experimental details; Results and discussion; Conclusion.

Examines the electrical properties of semiconducting iron disilicide (FeSi[sub2]) thin films. Information on the furnace annealing of electron-beam deposited iron layers; Analysis of the behavior of the films through the use of x-ray diffraction; Investigation of optical transitions at varying degrees of energy.

The competitive incorporation of Al and In in AllnGaN alloys grown by molecular beam epitaxy (MBE) and its effect on the spatial distribution of the CL emission is investigated. Built-in strain in the layer determines the preferential incorporation of In atoms to the alloy in regions where the strain is relaxed via the formation of pinholes.

Photoluminescence and Raman spectroscopy is used to study Ga-face AlGaN/GaN heterostructures with different sheet carrier concentration. The causes for discrepancies between the calculated and experimentally determined sheet carrier densities are discussed.

Reports on the Raman scattering of hydrogen- and deuterium-implanted cadmium fluoride. Effects of proton and deuteron on the Raman spectra of cadmium fluoride crystals; Origin of Raman peaks observed in semiconducting cadmium fluoride; Functions of the Raman spectra.