A. K. Ghosh

a‐Si : H produced by high‐temperature thermal decomposition of silane

Hydrogenated amorphous silicon has been deposited by a new technique of thermal decomposition of silane from a hot tungsten or carbon foil heated to about 1600 °C. Initial measurements indicate that the resulting films have a fairly high photoresponse. Introduction of ammonia along with silane is seen to enhance the photoconductivity quite significantly.

Optical and electrical properties of evaporated amorphous silicon with hydrogen

The optical and electrical properties of evaporated amorphous silicon with hydrogen have been studied under various deposition conditions. Infrared measurements indicate that the hydrogen content of the films are comparable to a‐Si : H films produced by other techniques. The optical‐absorption coefficient below the band gap of ∼1.55 eV was measured to be ∼100 cm−1 for samples made at deposition temperatures of ∼275–325 °C. For these samples the photoresponse at room temperature and the temperature dependence of the conductivities were studied. Dark conductivities were found to be thermally activated for T≳300 K with activation energies of ∼0.75 eV. We found type‐1 photoconductivity and investigated its dependence on the light intensity. When samples were heated to ∼175 °C in a vacuum and then exposed to air, they exhibited time‐dependent increases in the dark conductivity and photoconductivity. This effect was reversible by a reanneal in a vacuum. High‐temperature anneals to ∼450 °C increased the optical ...

Some properties of evaporated amorphous silicon made with atomic hydrogen

We describe measurements on a‐Si films made by adding atomic hydrogen during evaporation of silicon. The material has conductivity comparable to that formed by silane decomposition and is also photoconducting. The photocurrent in these initial experiments is smaller than in the bes silane‐produced films.

The effects of irradiation at cryogenic temperatures and electron irradiation on Tc and the transport properties of A-15 superconductors☆

The electrical resistivity ρ and Tc have been measured on vapor deposited films of Nb3Ge and Nb3Sn subjected to α-particle and electron irradiation. Both Nb3Sn and Nb3Ge films held at 30 K were irradiated with 2.5 MeV α particles. Tc and ρ0, the electrical resistivity at 25 K, were measured in situ as a function of fluence without warming up the samples. In addition, Nb3Sn films held at 50°C were irradiated with 2.0 MeV electrons. Tc was found to correlate with ρ0, which implies that Tc is affected by the total defect concentration. Of particular interest is the shape of the Tc vs. ρ0 curve for low fluences. A discussion will be given of why this low fluence region is important in distinguishing between different models of Tc depressions. We believe that the strong depression in Tc with increasing ρ0 (until saturation of Tc) is due to smearing of the density of states. The density of states in the damaged films was estimated from critical field data, along with measurement of ρ0.

Some properties of dc glow discharge amorphous silicon solar cells

A study of the internal yield, depletion width, and absorption constant is presented for dc glow discharge P‐I‐N amorphous silicon films. Internal yields of ∼0.9 at 475 nm and depletion widths as large as 0.37 μm were observed at low illumination levels and were characteristic of the better cells. The absorption constant as a function of wavelength showed no anomalies and was comparable to rf glow discharge films with an optical gap of 1.68 eV. A unique aspect of these cells is that the top P layer is amorphous boron.

Superconductivity in irradiated A-15 compounds at low fluences II. Alpha-particle-irradiated Nb3Sn and Nb3Ge

The Tcbehavior of vapor-deposited Nb3Ge and Nb3Sn is examined as a function of low-fluence alpha-particle irradiation. It is found that for Nb3Sn with ϱ ∼ 15 ΜΩ-cm the Tcis insensitive to low doses of radiation, whereas Nb3Ge with ϱ0 ∼ 50 ΜΩ-cm has its Tcdepressed immediately with irradiation. It is suggested that the Tcbehavior of A-15 superconductors in the regime of small dose is strongly influenced by the initial state of the sample. Furthermore, it is argued that the behavior of the Tcwith dose can be qualitatively explained by considering a sharp structure in the density of states N(E), the smearing of which by defects leads to a depression in Tc.

Density of states and T/sub c/ of disordered A15 compounds

In this paper various data for the depression of T/sub c/ and N(O) are presented for a wide class of A15 materials. The question of disorder and the limits on T/sub c/ in these materials are discussed.