Electrical properties of in situ phosphorus- and boron-doped polycrystalline SiGeC films

Abstract

The sheet resistance, effective carrier concentration, and Hall mobility of in situ boron- and phosphorus-doped polycrystalline Si0.82−yGe0.18Cy films are presented for carbon contents between 0% and 4%. Phosphorus and boron doping levels of 4×1019 and 2×1020 cm−3 were achieved for the n- and p-type layers, respectively, and remained largely unaffected by carbon content. The phosphorus-doped films showed a dramatic increase in sheet resistivity and a corresponding drop in effective carrier concentration and Hall mobility. In contrast, the boron-doped films showed only a minor increase in resistivity. This is attributed to interstitial carbon increasing the defect density and also shifting the defect energy levels at the grain boundaries towards the valence band. This causes an increase in the grain-boundary energy barrier in n-type layers, but leaves the p-type layers largely unaffected.