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 0.96 Si 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.