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.

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.

关键词： Amorphous semiconductors   Elemental semiconductors   Germanium   Electrical properties   Sputter deposition  

摘要： Hydrogenated amorphous germanium‐nitrogen alloys (a‐GeN _x :H) were synthesized as a new group of amorphous semiconductors by rf(13.56 MHz) reactive sputtering of a Ge target in a gas mixture of Ar+N₂+H₂ under a variety of deposition conditions such as gas ratio, rf‐discharge power, and substrate temperature. Structural, optical, and electrical properties of those a‐GeN _x :H alloys were systematically measured and are discussed in relation to their preparation conditions. The optical band gapE _{0 4} of a‐GeN _x :H alloys could be continuously controlled in the range from 1.1 eV to 3.3 eV primarily depending on the atomic N/Ge ratio in the film. The role of hydrogen and nitrogen in the optical and electrical properties of the material is also crucially demonstrated.

关键词： Amorphous semiconductors   Transistors   Elemental semiconductors   Germanium   Hole mobility  

摘要： The first hydrogenated amorphousgermanium and hydrogenated amorphous silicon‐germanium alloy field‐effect transistors with appreciable field‐effect response in n‐ and p‐channel modes were developed by reducing the dihydride content in the films. Field‐effect mobilities were derived from transistor characteristics. Hole mobilities are superior to those in pure hydrogenated amorphous silicon which offers the opportunity for improved thin‐film devices.

标准号: NF P26-411/AM-1970