Low energy (55 KeV) Osmium ( Os− ) negative ion beam was used to implant (5×1016 atoms/cm2 ) into p-type-Si (100). The implantation was performed with the ion source of a National Electrostatic Corp. 3 MV Tandem accelerator. The implanted sample was subsequently annealed at 650 °C in a gas mixture that was 4% H2 + 96% Ar. Rutherford Backscattering spectrometry (RBS) analysis with 1.5 MeV Alpha particles was used to monitor the precipitate formation. Photoluminescence (PL) measurements were also performed to study possible applications of silicides in light emission. Cross-sectional Scanning Electron Microscopy (X-SEM) was performed for topographic image of the implanted region. RBS along with PL measurements indicate that the presence of osmium silicide (Os2Si3) phase for light emission in the implanted region of the sample.

Hydrogenated nanocrystalline silicon (nc-Si:H) has strong potential to replace the hydrogenated amorphous silicon (a-Si:H) in thin film transistors (TFTs) due to its compatibility with the current industrial a-Si:H processes, and its better threshold voltage stability [1]. In this paper, we present an experimental TFT array backplane for direct conversion X-ray detector, using inverted staggered bottom gate nc-Si:H TFT as switching element. The TFTs employed a nc-Si:H/a-Si:H bilayer as the channel layer and hydrogenated amorphous silicon nitride (a-SiNx) as the gate dielectric; both layers deposited by plasma enhanced chemical vapor deposition (PECVD) at 280°C. Each pixel consists of a switching TFT, a charge storage capacitor (Cpx ), and a mushroom electrode which serves as the bottom contact for X-ray detector such as amorphous selenium photoconductor. The chemical composition of the a-SiNx was studied by Fourier transform infrared spectroscopy. Current-voltage measurements of the a-SiNx film demonstrate that a breakdown field of 4.3 MV/cm.. TFTs in the array exhibits a field effect mobility (μEF ) of 0.15 cm2/V·s, a threshold voltage (VTh ) of 5.71 V, and a subthreshold leakage current (Isub ) of 10−10 A. The fabrication sequence and TFT characteristics will be discussed in details.

This paper describes the study of an electron-trapping defect which underwent significant configurational relaxation in oxygen contaminated hydrogenated amorphous silicon-germanium (a-Si,Ge:H) alloys grown by hot-wire chemical vapor deposition. An unusual two-step electron emission from this relaxed defect is studied using junction-capacitance-based measurements. In this work, we monitor the recovery of the relaxed defect after filling it by photoexcited electrons and also by electrons injected with a voltage filling pulse. The dependence of the transient shape on filling pulse time is described. We have also performed experiments which clearly demonstrate that this is a bulk defect and exclude contributions from any additional blocking junctions.

We report structural and electronic properties of Aligned-Crystalline Si (ACSi) films on glass substrates. These films show enhanced majority carrier mobilities and minority carrier lifetimes with increasing crystallinity, i.e., with improving alignment and connectivity of the grains. A 0.4-μm-thick ACSi film with a total grain mosaic spread of 4.2° showed Hall mobility of 47 cm2/V.s for a p-type doping concentration of 1.9×1018 cm−3. A prototype n+/p/p+–type diode fabricated using a 4.2-μm-thick ACSi film showed minority carrier lifetime of ∼3.5 μs and estimated diffusion length of ∼30 μm in the p layer with a doping concentration of 5×1016 cm−3.

Stability is an important issue for the application of TFTs. In this paper, we present the effects of humidity and temperature on the stability of inverted-staggered back-channel-cut a-Si:H TFTs with various conduction channel layer thickness. We evaluated the stability of on-plastic TFTs of different conduction layer thicknesses made at a process temperature of 150°C on 51-μm thick Kapton polyimide foil substrates.. With conduction channel layer thickness of 50nm, humidity reversibly varies the characteristics of TFTs, but TFTs of conduction layer thickness greater than 100 nm is pretty immune to the humidity change. The temperature dependent stability and characteristics of TFTs were analyzed from 20°C to 60°C. Rising temperature from 20°C to 56°C, the threshold voltage (Vt) drops about 2 volts; on-off current ratio decreases by one order of magnitude mainly due to thermally excited carriers in the off-region.

Junction capacitance measurements were used to characterize the properties of nanocrystalline silicon (nc-Si:H) solar cells. These methods included drive-level capacitance profiling (DLCP) to obtain spatially-resolved defect densities, as well as transient photocapacitance (TPC) and transient photocurrent (TPI) spectra to reveal optically responsive states in the band-gap, and to estimate minority carrier behavior before and after lightsoaking. Crystalline volume fractions were estimated using Raman spectroscopy. Previously we had identified at least two types of distinct behaviors in such nc-Si:H materials that depended on the crystalline volume fraction. Here, in one case, we report results indicating that both types of behavior can occur in a single sample, possibly indicating that the structural properties of that sample have evolved during growth.

In this paper we present results on the optimization of device architectures for colour and imaging applications, using a device with a TCO/pinpi'n'/TCO configuration. A set of different devices with different intrinsic back layers are analysed.

The effect of the applied voltage on the color selectivity is discussed. Results show that the spectral response curves demonstrate rather good separation between the red, green and blue basic colors. Combining the information obtained under positive and negative applied bias a colour image is acquired without colour filters or pixel architecture. A low level image processing algorithm is used for the colour image reconstruction.

Fast epitaxial growth of several microns thick Si at glass-compatible temperatures by the hot-wire CVD technique is investigated, for film Si photovoltaic and other applications. Growth temperature determines the growth phase (epitaxial or disordered) and affects the growth rate, possibly due to the different hydrogen coverage. Stable epitaxy proceeds robustly in several different growth chemistry regimes at substrate temperatures above 600°C. The resulting films exhibit low defect concentrations and high carrier mobilities.

Thin film solar cells based on polycrystalline silicon are an appealing option combining the advantages of thin film technologies, namely low cost, and the superior electrical properties of crystalline silicon. The specific structure aimed at in this work uses the relatively simple contacting scheme used in amorphous silicon thin film solar cells which relies on a front contact consisting of a transparent conducting oxide (TCO). Electron beam evaporation is applied as preparation method for the silicon films with high deposition rate. Solid phase crystallization (SPC) is used to crystallize the silicon films after deposition.

In this work the properties of as-deposited and crystallized silicon films produced by e beam evaporation are investigated as a function of deposition temperature. It is shown that the largest crystallites are obtained for deposition around 300 °C and subsequent treatment at 600 °C, while deposition at higher temperatures leads to small crystal grains which are not changed significantly during SPC.

Solar cells have been prepared on TCO-coated glass and were studied by measurements of the external quantum efficiency.

Solar cells based on hydrogenated nanocrystalline silicon (nc-Si:H) have demonstrated significant improvement in the last few years. From the standpoint of commercial viability, good quality nc-Si:H films must be deposited at a high rate. In this paper, we present the results of our investigations on obtaining high quality nc-Si:H and a-Si:H films and solar cells over large areas using high deposition rate. We have employed the modified very high frequency (MVHF) glow discharge technique to realize high-rate deposition. Modeling studies were conducted to attain good spatial uniformity of electric field over a large area (15”×1”) MVHF cathode for nc-Si:H deposition. A comparative study has been carried out between the RF and MVHF plasma deposited a-Si:H and nc-Si:H single-junction and a-Si:H/nc-Si:H double-junction solar cells. By optimizing the nc-Si:H cell and the tunnel/recombination junctions, we have obtained an initial aperture-area (460 cm2) efficiency of 11.9% for a-Si:H/nc-Si:H double-junction cells using conventional RF (13.56 MHz) plasma deposition. The deposition rate was 3 Å/sec. Results on solar cells made with MVHF will also be presented.