Role of grains in protocrystalline silicon layers grown at very low substrate temperatures and studied by atomic force microscopy

We have investigated the role of the sample thickness and silane dilution on the structure and electronic properties of protocrystalline silicon thin films deposited at very low substrate temperatures (similar to 80 degreesC). Coincidence of the maxima in surface roughness and ambipolar diffusion length (greater than or similar to 100 nm) with formation of the network of interconnected crystalline grain aggregates was observed. While the presence of the isolated grain aggregates improves the photoconductive proper-ties before the percolation threshold is reached, further increase in crystallinity may have opposite effect due to detrimental role of increasing concentration of the defective grain boundaries. (C) 2002 Elsevier Science B.V. All rights reserved.