Characterization of Short-Wavelength-Selective a-Si:H MSM Photoconductors for Large-Area Digital-Imaging Applications
Photoconductor-type photodetectors are attractive as sensors due to their compatibility with thin-film-transistor (TFT) fabrication processes. Since they exhibit photogain, photoconductor detectors have better or comparable responsivity and quantum efficiency (QE) compared to p-i-n photodiodes. In this paper, the operation of metal-semiconductor-metal photoconductor-based photodetectors using aluminum electrodes and thin hydrogenated amorphous-silicon (a-Si) films is investigated. The experimental results of photocurrent measurements, as well as the responsivity and QE for different a-Si film thicknesses, bias voltages, and electrode gaps, are presented. Integration with TFT fabrication and its application in large-area digital imaging are discussed.
Adjustable ultraviolet-sensitive detectors based on amorphous silicon
Thin-film detectors made of hydrogenated amorphous silicon (a-Si:H) and amorphous silicon carbide (a-SiC:H) with adjustable sensitivity in the ultraviolet (UV) spectrum were developed. Thin PIN diodes deposited on glass substrates in N–I–P layer sequence with a total thickness of down to 33 nm and a semitransparent Ag front contact were fabricated. The optimized diodes with a 10 nm Ag contact exhibit spectral response values above 80 mA/W in the wavelength range from 295 to 395 nm with a maximum of 91 mA/W at 320 nm. For longer wavelengths, the spectral response drops by 50% at 450 nm. Increasing the thickness of the Ag front contact leads to a narrowing of the spectral response at around 320 nm, which allows the adjustment from a broad UV to a selective UV–B-sensitive detector.
Low frequency plasma deposition and characterization of Si1−xGex:H,F films
Abstract Si–Ge alloys have been widely studied because of their wide spread applications. RF discharge is a conventionally adopted technique for the deposition of Si–Ge films. Little is known about the deposition and properties of Si–Ge films in low frequency plasmas. The present work concerns an investigation of growth, structure and electronic properties of a-Si1−xGex films deposited by low frequency PECVD, where x is the Ge content in the gas phase, from SiH4 and GeF4 as source gases, and H2 and Ar for dilution. There is no deposition of the film without dilution, while in both cases of H- and Ar-dilution, the growth is observed over the entire x range. However, the deposition rate depends on x and decreases faster in the case of Ar dilution. Both, SIMS and Raman spectra data, demonstrate that incorporation of Ge in the solid phase reaches saturation at x≈0.5. In Raman spectra, the scattering related to Si crystalline phase (line at k=520 cm−1) increases and new lines in vicinity of k=480 cm−1 appear with x. It suggests a change in the local structure around Si atoms. The electrical properties were studied by measurements of the temperature dependence of the conductivity. The reduction of the activation energy from 0.86 to 0.39 eV and the increase of room temperature conductivity from 1 × 10−9 to 2.1 × 10−4 Ω−1 cm−1 were observed with the changes of x from 0 (Si) to 1(Ge). No correlation between pre-exponent factor of conductivity σ0 and activation energy was observed in the samples studied in contrast with a-Si–Ge films deposited from mixtures with GeH4.