Relationship between electrical properties and structure in uniaxially oriented polycrystalline silicon films

Undoped polycrystalline Si (poly-Si) films were prepared on a fused quartz substrate as a function of the rf power (0–30 W) and deposition temperature (620–770 °C) by a plasma-enhanced chemical vapor deposition method. The preferential orientation to a random, 〈100〉 or 〈110〉 crystal axis can be selected by changing some of these preparation conditions. Electron spin resonance (ESR) and the dependence of the dark conductivity σd on the measurement temperature T have been investigated to examine how the structure of the grain boundary depends on the preferential orientation (P.O.) and affects the electrical properties. An enhancement in the degree of P.O. is found to lead to a reduction in the local ESR spin density within the boundary region and g factor. Also, for the films with a random or weak P.O., σd as a function of 1/T exhibits a kink around room temperature, and the conduction in a low-T range is interpreted in terms of the model of variable range hopping within the boundary region. These results and the characteristics of thin-film transistors fabricated on the poly-Si films are discussed in terms of the structural change of the boundary region.