Deposition of device quality amorphous silicon by hot-wire CVD

In this paper we present the results of the optimization of hydrogenated amorphous silicon films deposited by the hot-wire method in a larger area system. Using a two-wire design, we succeeded in depositing films that exhibit uniform electrical properties over the whole 4 " x 4 " Coming 7059 glass substrate. At a substrate temperature of 430 degrees C and a pressure of 20 mu bar we obtained a growth rate of similar to 2 nm/s. The temperature of the tungsten filaments was kept at 1850 degrees C. The values for the photoconductivity and dark conductivity were 8.9x10(-6) S/cm and 1.6x10(-10) S/cm respectively, whereas the ambipolar diffusion length, as measured with the Steady-Slate Photocarrier Grating technique (SSPG), amounted to 145 nm. This value is higher than for our device quality glow-discharge (GD) films, which yield devices with efficiencies higher than 10%. The hydrogen content was 9.5%. We report on the density-of-states (DOS) distribution in the films, which was measured with the techniques of Thermally Stimulated Conductivity (TSC) and Constant Photocurrent Method (CPM). Furthermore, we describe the behavior of the electrical properties on light-induced degradation. Finally, we incorporated these films in solar cells, using conventional GD doped layers. Preliminary SS/n-i-p/ITO devices yielded efficiencies in excess of 3% under 100 mW/cm(2) AM1.5 illumination. Further work concerning the optimization of the interfaces is in progress.