Deposition and Properties of Silicon on Graphite Substrates

Abstract

Polycrystalline silicon has been deposited on low-cost graphite substrates by the thermal decomposition Of silane and thermal reduction of trichlorosilane with hydrogen in a gas flow system. The microstructures and crystallographic properties of deposited silicon were studied over a wide range of deposition conditions by metallographic and x-ray techniques, respectively. The observed differences in the properties of silicon layers deposited by silane and trichlorosilane processes were attributed to the difference in the chemical reversibility of the reactions. The microstructure of silicon deposited by the trichlorosilane process was improved by the addition of hydrogen chloride to the reactant mixture. Solar cells were prepared from silicon layers deposited on graphite substrates by a one-step process using silane or trichlorosilane and appropriate dopants, and AMO efficiencies of up to 1.5% were obtained.The current interest in the terrestrial utilization of solar energy by photovoltaic converters has stimulated considerable research and development efforts in lowcost solar cells. Silicon solar cells which have been used reliably in spacecrafts for many years are manufactured from semiconductor-grade silicon and are far too expensive for terrestrial applications. The use of polycrystalline silicon layers on suitable substrates is considered as a promising approach for the fabrication of low-cost solar cells (1). In this approach, the selection of the substrate is an important consideration. Steel is the most economical choice for a large area substrate; however, polycrystalline silicon solar cells deposited on steel substrates were found to have low conversion efficiencies because of the incompatibility of the properties of iron and silicon (2). Graphite is more compatible with silicon in properties than steel. Several types of low-cost graphite have a thermal expansion coefficient similar to that of silicon. Graphite is relatively inert toward silicon at temperatures used for the deposition of silicon. Also, graphite has high thermal and electrical conductivities and may be used as an ohmic contact to the solar cell. Thus, graphite appears to be the most promising substrate for low-cost silicon solar cells at present.In this work, the thermal decomposition of silane and the thermal reduction of trichlorosilane with hydrogen have been used for the deposition of silicon on graphite substrates. The microstructure and crystallographic properties of silicon deposited under a wide range of conditions were studied. Using appropriate dopants during the deposition process, p-n junction solar cell structures were prepared and characterized. The experimental procedures used for the deposition process and the properties of deposited silicon and solar cells are discussed in this paper.

Synthesis, Microstructure, and Cathodoluminescence of [0001]-Oriented GaN Nanorods Grown on Conductive Graphite Substrate

“…Compared with Si and other substrates mentioned above, graphite is more stable at high temperature and exhibits excellent performance in electrical and thermal conductivities, and a lower thermal expansion coefficient. The deposition of bulky semiconductor materials on graphite has been investigated thirty years ago and series of works have been carried out. As a typical example, multilayer graphene has been utilized as a transparent conducting electrode , for the building of high-efficiency light-emitting diodes (LEDs).…”

Electrical Properties of n‐Type Polycrystalline Indium Phosphide Films

“…Inserting Eq. [2] and [3] into Eq. [4], the following equation concerning nl is obtained ni 2 -~1 -An = 0 [5] where A is…”

“…Polycrystalline films of various semiconductors have been used in fabricating low cost solar cells (1)(2)(3). Consequently, the growth and structure of polycrystalline indium phosphide films have been investigated by the authors (4,5).…”

Large grain polycrystalline silicon via chemical vapor deposition

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Often the objective was to increase grain size. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Often the objective was to increase grain size.…”

“…Chu, Mollenkopf, and Chu 20 have examined the effect of high temperatures on the morphology of CVD Si. Foremost is the use of high deposition temperatures and reduced reactor pressures.…”