Comparison of Doping of Ge_y Si_1-y:H (y>0.95) Films Deposited by Low Frequency PECVD at High (300°C) and Low (160°C) Temperatures

Abstract

In this work we present the results of comparative study n- and p-doping of Ge:H and Ge_0.96Si_0.04 :H films deposited by LF PECVD at high deposition temperature (HT) T_d=300°C and low deposition temperature (LT) T_d=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 σ_RT and activation energy E_a 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 E_a=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 E_a 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 E_a(max) at the same doping with E_a(max)=0.47 eV for HT and E_a(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 E_a and the smallest E_a=0.27 eV was obtained at [B]_gas=0.18% for HT films and E_a=0.33 eV at [B]_gas=0.14% for LH films.