Comparison of Doping of Gey Si1-y:H (y>0.95) Films Deposited by Low Frequency PECVD at High (300°C) and Low (160°C) Temperatures

Abstract

ABSTRACTIn this work we present the results of comparative study n- and p-doping of Ge:H and Ge0.96Si0.04 :H films deposited by LF PECVD at high deposition temperature (HT) Td=300°C and low deposition temperature (LT) Td=160°C. The concentration of boron and phosphorus in solid phase was measured by means of SIMS technique. Such parameters as spectral dependence of absorption coefficient, room temperature conductivity σRT and activation energy Ea for both intrinsic and doped films were obtained. The doping range studied in gas phase was for boron [B]gas= 0 to 0.15% and for phosphorus [P]gas= 0 to 0.2%. In general effect of deposition temperature on P and B doping has been demonstrated. For LT films changes of [P]gas=0.04% to 0.22% resulted in more than 2 orders increasing conductivity and reducing activation energy from Ea=0.28 to 0.16 eV. HT films in the range of [P]gas=0.04% to 0.2% demonstrated saturation of conductivity. HT films showed continuous reducing Ea with increase of [P]gas. In the case of boron doping both HT and LT films had a minimum of conductivity at certain values of [B]gas=0.05% (LT films) and 0.04% (HT films) and related maximums of activation energy Ea(max) at the same doping with Ea(max)=0.47 eV for HT and Ea(max)=0.53 eV for LT films. It suggests a compensation of electron conductivity in un-doped films for low B doping. Further raising [B]gas leads to reducing Ea and the smallest Ea=0.27 eV was obtained at [B]gas=0.18% for HT films and Ea=0.33 eV at [B]gas=0.14% for LH films.