Effect of Pressure and Temperature on the Electrical Properties of LPCVD Silicon-Germanium Thin Films

摘要

The electrical properties of polycrystalline silicon-germanium films formed by low pressure chemical vapor deposition using SiH4 and a GeH_4/H_2 mixture are investigated. The effects of the deposition pressure and temperature on carrier concentration and resistivity made by Hall measurements are studied. We show that the germanium incorporation is linked to the deposition temperature whereas the total pressure has no influence. All the films are amorphous. Electrical properties of these layers are found very sensitive to annealing, deposition temperature and total pressure. However hole concentration and resistivity do not have a particular trend with the deposition parameters because they are linked on one hand to the germanium incorporation and on the other hand to the structure of the layers depending on deposition conditions. So we find hole concentrations up to around 10~(14) cm~(-1), hole mobilities up to around 37 cm~2/Vs and resistivities up to 3500 Ω.cm. Consequently, as the resistivity obtained is low and the hole concentration is high, we suppose that the presence of germanium in the silicon lattice introduces an acceptor level in the bottom part of the gap.