Amorphous silicon-germanium (a-Si_0.01Ge_0.99:H) doped with phosphorous deposited by LF PECVD and its electrical and optical characteristics

Abstract

Amorphous silicon-germanium (a-Si_0.01Ge_0.99:H) thin film, practically amorphous germanium with small concentration of silicon, were deposited by the low frequency PECVD technique under different flow gas of phosphine in the range of QPH₃ = 20 to 100 sccm. In this range the phosphorous concentration in gas phase was calculated as X_P= 4 to 20 % which resulted in a content in solid phase [P]_sol=0.12% - 0.4%. The P content of the solid phase was measured by SIMS profiling and it was also observed a preferential incorporation of phosphorous in the range of [P]_sol=0.12% - 0.3%. Hydrogen concentration in the films was determined from FTIR and SIMS measurements. The activation energy was determined by measuring the temperature dependence of conductivity in DC regime in a vacuum thermostat. For the a-Si_0.01Ge_0.99:H films it is found that the activation energy have a minimum, (Ea= 0.15eV), its conductivity at room temperature have a maximum and there is a minimum of of both band tail and deep localized state for a phosphorous incorporation in solid phase [P] =0.28%.