Device‐quality hydrogenated amorphous silicon containing as little as 1/10 the bonded H observed in device‐quality glow discharge films have been deposited by thermal decomposition of silane on a heated filament. These low H content films show an Urbach edge width of 50 mV and a spin density of ∼1/100 as large as that of glow discharge films containing comparable amounts of H. High substrate temperatures, deposition in a high flux of atomic H, and lack of energetic particle bombardment are suggested as reasons for this behavior.

Deposition of device quality, low H content amorphous silicon

Solar Photovoltaics R&D at the Tipping Point: A 2005 Technology Overview

This review centers on the status, and future directions of the cell and module technologies, with emphasis on the research and development aspects. The framework is established with a consideration of the historical parameters of photovoltaics and each particular technology approach. The problems and strengths of the single-crystal, polycrystalline, and amorphous technologies are discussed, compared, and assessed. Single- and multiple junction or tandem cell configurations are evaluated for performance, processing, and engineering criteria. Thin-film technologies are highlighted as emerging, low-cost options for terrestrial applications and markets. Discussions focus on the fundamental building block for the photovoltaic system, the solar cell, but important module developments and issues are cited. Future research and technology directions are examined, including issues that are considered important for the development of the specific materials, cell, and module approaches. Novel technologies and new research areas are surveyed as potential photovoltaic options of the future.

Photovoltaics: A review of cell and module technologies

The absolute densities of H atoms produced in catalytic chemical vapor deposition (Cat-CVD or hot-wire CVD) processes were determined by employing two-photon laser-induced fluorescence and vacuum ultraviolet absorption techniques. The H-atom density in the gas phase increases exponentially with increases in the catalyzer temperature in the presence of pure H2. When the catalyzer temperature was 2200 K, the absolute density in the presence of 5.6 Pa of H2 (150 sccm in flow rate) was as high as 1.5×1014 cm−3 at a point 10 cm from the catalyzer. This density is one or two orders of magnitude higher than those observed in typical plasma-enhanced chemical vapor-deposition processes. The H-atom density decreases sharply with the addition of SiH4. When 0.1 Pa of SiH4 was added, the steady-state density decreased to 7×1012 cm−3. This sharp decrease can primarily be ascribed to the loss processes on chamber walls.

Direct detection of H atoms in the catalytic chemical vapor deposition of the SiH4/H2 system

▪ Abstract Hydrogenated amorphous silicon (a-Si:H) exhibits a metastable light-induced degradation of its optoelectronic properties that is called the Staebler-Wronski effect, after its discoverers. This degradation effect is associated with the relatively high diffusion coefficient of hydrogen and the changes in local bonding coordination promoted by hydrogen. Reviewed are the fundamental aspects of the interplay between hydrogen and electronic energy states that form the basis of competing microscopic models for explaining the degradation effect. These models are tested against the latest experimental observations, and material and preparation parameters that reduce the Staebler-Wronski effect are discussed.

Development in Understanding and Controlling the Staebler-Wronski Effect in a-Si:H

Small-angle X-ray scattering studies of microvoids in a-SiC:H and a-Si:H

Small-angle X-ray scattering (SAXS) measurements on a series of a-SiC:H alloy films deposited in a glow discharge reactor using SiH/sub 4//CH/sub 4/ gas mixtures are discussed It was found that the introduction of C into the a-Si matrix produces a large SAXS signal, which suggests a sizable microvoid density, and which further increases with increasing C content A Guinier analysis shows that these microvoids are spherical and have an average radius of approximately 6 AA, which increases only slightly with C content Other measurements (infrared, photoconductivity, film density, optical) made on identically prepared material are included to identify the possible origins of these microvoids and to determine how they affect material quality >

A.H. Mahan

Papers

Deposition of device quality, low H content amorphous silicon

Small-angle X-ray scattering studies of microvoids in a-SiC:H and a-Si:H

Small angle X-ray scattering from microvoids in the a-SiC:H alloy