摘要： Thermomechanical properties (stress, thermal expansion coefficient, and elastic modulus) of a-GeNx:H thin films prepared by the rf sputtering technique are reported. Stress measurements are made using a Dektak profilometer to determine the radius of curvature of the film/substrate structure. The majority of the films prepared in this work have compressive stress. A second apparatus based on the deflection of a He-Ne laser beam is used to determine the thermal expansion coefficient and the Young's modulus/(1-Poisson's ratio) by the thermally induced bending method. They depend strongly on the nitrogen concentration.

摘要： A study of the band-gap tailoring of amorphous germanium nitrogen alloys is presented. They have been prepared by the rf reactive sputtering technique, using a c-Ge target in an Ar + NH3 atmosphere. The alloy composition is found to be strongly dependent on the deposition conditions. The optical gap of the material could be tailored from approximately 1.0 to about 3.0 eV by varying the rf power, substrate temperature, nitrogen and hydrogen partial pressures. The rf power, and not the gas composition, is found to be the most important parameter in determining the nitrogen concentration. The hydrogen concentration, on the other hand, has a small influence on the band gap, while the temperature plays an important role on the determination of the alloy structure.

关键词： SILICON ALLOYS   GERMANIUM ALLOYS   HYDROGENATION   AMORPHOUS STATE   FILM GROWTH   CHEMICAL VAPOR DEPOSITION   CHEMICAL REACTIONS   PRECURSOR   OPTICAL PROPERTIES  

摘要： We suggest that the role of hydrogen dilution in the improvement of the quality of hydrogenated amorphous silicon germanium alloys is to alter the relative contribution of the short and long lifetime precursors to film growth which are deleterious and beneficient, respectively. In order to circumvent the preferential depletion of germane when mixed with silane, we have used low power disilane-germane discharges and thereby obtained films with an optical gap < 1.5 eV having similar Urbach tail width and defect absorption, with and without hydrogen dilution. (C) 1995 American Institute of Physics.

摘要： We use spin-dependent photo-conductivity (SDPC) to study the recombination process of photo-excited carriers in hydrogenated amorphous silicon germanium alloys (a-SixGe1-x:H). The incorporation of Ge is marked by a sudden change in the SDPC signal ( -Delta sigma/sigma ) from (a-Si:H)-like to (a-Ge:H)-like. The Ge atoms create new states which dominate transport and recombination of photo-created free carriers. In particular, the SDPC lineshape analysis indicates that the a-Si:H conduction band tail is affected by alloying with small concentrations of germanium.

摘要： Amorphous hydrogenated silicon-germanium alloys grown by photo-CVD have been studied using a variety of steady-state and transient junction-capacitance techniques. The dependence of the electronic mobility gap structure, the density of deep defects, and the carrier trapping properties on the germanium content has been investigated systematically. The Urbach tail slope is found to be nearly constant over the whole alloy range. The dominant defect band is found to track the midgap energy position, and the density of deep defects increases exponentially with increasing germanium content. These results are fully consistent with weak bond breaking theories and suggest that the quality of amorphous silicon-germanium alloys and a-Ge:H is inherently inferior to pure a-Si:H materials.

关键词： Band gap effect   Carrier generation   Hydrogen dilution effect   Recombination loss   Silicon germanium alloy   Solar technology  

摘要： The spectral dependence of carrier generation and recombination loss in a-SiGe:H samples having band gaps between 1.74 eV and 1.35 eV was studied in the Schottky barrier solar cell device structure. The active a-SiGe:H layers were of identical thickness (1 mum). The effect of hydrogen dilution of the source gases (silane and germane) on the generation and recombination characteristics was also studied. It has been observed that the net optical generation of carriers increases almost linearly with the lowering of the band gap but is independent of the localised states. Net recombination loss, on the other hand, increases with defect states but cannot be fully explained by taking into account the neutral defect centers alone. Within the above mentioned band gap range, it has been observed that the competing processes of generation and recombination resulted in a maximum short circuit current for a-SiGe:H samples of 1.44 eV band gap.

摘要： A first step in an experiment series aimed at establishing the undercooling properties of eutectic alloys embedded in an inert matrix under microgravity conditions was performed aboard the Mir orbital laboratory. Here metallic samples of the Ag-Ge eutectic system were embedded in a boron trioxide matrix and processed in the CSK-1 space furnace. The results demonstrated a performance of the sample containment and furnace operation as expected. The undercooled melt droplets solidified spontaneously without contacting container walls and with no indication of sedimentation. Microgravity effects are apparent from the microstructure of polished cross sections. The structure of the primary silver or germanium precipitates is significantly finer and shows a more even distribution for the space processed samples as compared to ground control samples. The germanium concentration in the silver precipitates is larger in space samples. Both these observations point to a larger undercooling in the microgravity processed samples, which however could not be measured directly in this preliminary test. In addition, an unexpected occurrence of a grouping of germanium crystallites in a 5-fold symmetry was observed in the flight samples only.

关键词： Amorphous films  

摘要： A significant improvement in structural, optical and electrical properties of a-SiGe:H films grown by the photochemical vapour deposition method has been achieved through a selection of chamber pressure, substrate temperature and hydrogen dilution. By varying these process parameters, a-SiGe:H films having dominant silicon and germanium monohydride bonds were produced (from IR analysis) which have less microstructure related disorder, sharp valence band tail width (E0) and low dangling-bond density (N(s)). As a consequence the magnitude of the photogenerated carrier (generation efficiency-mobility-lifetime product, etamutau) improved by two orders of magnitude. This resulted in a photoconductivity (sigma(Ph)) of 10(-5) S cm-1 along with a dark conductivity (sigma(D)) of 10(-10) S cm-1 for a-SiG:H film having a band gap of 1.5 eV.

关键词： X-Rays  

摘要： The tunability of synchrotron radiation was used to perform anomalous small-angle X-ray scattering (ASAXS) experiments on amorphous metal-germanium (a-MxGe100-x) alloys with the aim of detecting and characterizing composition modulation and phase separation. The combination of SAXS with the anomalous-dispersion effect allows the composition modulation to be distinguished from density fluctuations arising from voids and defects. Data gathered from a-FexGe100-x, a-WxGe100-x and a-MoxGe100-x samples in the low metal concentration regime show nanometer-scale composition modulation. In these samples the density of Ge atoms is uniform throughout. The small-angle X-ray scattering arises from fluctuations in the density of metal atoms. The position of the SAXS peak moves towards smaller values of the scattering vector with increased metal concentration indicating an increase in the correlation length of the composition fluctuations with increased metal content.

关键词： Amorphous semiconductors   Elemental semiconductors   Germanium   Optical properties   Sputtering  

摘要： A study of the macroscopic properties of a‐Ge:Sn and a‐Ge:Sn:H films is presented. The samples were prepared by the rf sputtering method on substrates held at 180?°C. Their composition and structure were characterized, and the transport and optical properties were studied. The role and influence of hydrogen on the general properties of the alloys have been established.