In recent years polycrystalline silicon deposited by chemical vapor deposition has become of importance in many semiconductor applications. The formation and properties of films deposited for different applications are reviewed in this paper, and the use of the films in semiconductor devices is discussed. The deposition temperature, gases, and impurities are found to have the major influence on the properties of the films. These deposition variables significantly affect the crystal

Chemically Vapor Deposited Polycrystalline-Silicon Films

Standard semiconductor measurements and techniques have been applied to undoped, high-purity polycrystalline silicon to determine its electronic properties. Resistivity and Hall mobility were determined as function of temperature, and the ability of polycrystalline silicon to form Schottky barriers and p−i−n junctions has been evaluated experimentally. Present results show Si grain boundaries behaving as p-type layers separating high-resistivity grains. An effective mobility, half the monocrystalline value, and an average carrier density in the 1015 cm−3 range are deduced. A qualitative model is discussed to describe present results.

Electronic properties of undoped polycrystalline silicon

EPR of the TiO4/Li center in crystalline quartz

P-I-N junctions in polycrystalline-silicon

Measurements and theoretical calculations have been made of the electrical properties of metal contacts to a polycrystalline Si‐Ge alloy (80 at.% Si) for a wide variety of conditions. Thin‐film contacts of W, Pb, and In have been formed on Si‐Ge phosphorus doped in the range 2×1018−1×1020 cm−3. For P concentrations near 2×1019 cm−3 we have produced samples having several interfacial oxide thicknesses. We have heat treated W contacts to this material to simulate elevated‐temperature aging effects of W thin‐film contacts on thermopiles. The differential conductance for all these various contacts has been measured as a function of bias voltage for temperatures from 1.1 to 300 K. Calculations of the differential conductance of these contacts have been performed using a metal‐insulator‐semiconductor model that accounts for tunneling, thermionic field emission, and thermionic emission. The calculationg generally cover the ranges of temperature, bias voltage, doping level, and oxide thickness used in the experiments. Graphical summaries of these calculations are presented which include doping dependence of the zero‐bias conductance ratio (300−4 K), the conductance values at several temperatures, and the location of the differential conductance minimum. Comparison of theory with experiment leads to the conclusion that the general features of the conductance characteristics can be predicted from the theory for certain ranges of oxide thickness and dopant concentration. Agreement appears to be best for thin oxides and P concentrations near 2×1019 cm−3, with both higher‐ and lower‐doped contacts behaving qualitatively as if their effective doping levels were nearer this value. This effect has interpreted in terms of phosphorus depletion or enhancement mechanisms occurring in the Si‐Ge depletion region during junction fabrication. When W contacts are hear treated after fabrication, agreement with theory improves. This believed to exhibit typical superconducting conductances at 1.1 K, thus showing that tunneling is, in fact, a major transport mechanism in Si‐Ge/metal junctions.

E. Muñoz-Merino

Papers

Metal‐polycrystalline silicon barriers