The role of carbon on the electrical properties of polycrystalline Si1-yCyand Si0.82-yGe0.18Cy films

A comparison is made of the electrical effects of carbon in n- and p-type i n situ doped polycrystalline Si1-yCy and Si0.82-yGe0.18Cy layers. Values of resistivity as a function of temperature, effective carrier concentration and Hall mobility are reported. The n-type polycrystalline Si1-yCy and Si0. 82-yGe0.18Cy films show dramatic increases in resistivity with carbon conte nt, rising from 0.044 Omega cm to 450 Omega cm (0 and 0.8% C) and 0.01 Omeg a cm to 2.4 Omega cm (0 and 0.6% C), respectively. In contrast, the increas e in B-doped films is much less severe, rising from 0.001 Omega cm to 0.939 Omega cm (0 and 7.9% C) and 0.003 Omega cm to 0.015 Omega cm (0 and 4% C) for the Si1-yCy and Si0.82-yGe0.18Cy layers, respectively. The grain bounda ry energy barrier, determined from the temperature dependence of the resist ivity, is found to vary as the square of the C content in the n-type polycr ystalline Si1-yCy and Si0.82-yGe0.18Cy layers, but linearly in the p-type S i1-yCy layers. The square law dependence seen in the n-type layers for C co ntents up to 0.9% is explained by an increase in the grain boundary trap de nsity due to the presence of carbon, whereas the linear relationship seen i n the p-type layers for C contents between 2% and 8% is explained by a shif t in the grain boundary trap energy toward the valence band. Finally, lower values of grain boundary energy barrier are obtained in p-type Si0.82-yGe0 .18Cy layers with a C content of 4% than in equivalent Si1-yCy layers, whic h could be explained by a larger shift in trap energy toward the valence ba nd. (C) 2001 American Institute of Physics.