Effect of phosphorus doping concentration on n-type Ge layer growth

The n-type Ge layers with various phosphorus doping concentrations were grown on p-type Si (100) wafers by using Rapid Thermal Chemical Vapor Deposition (RTCVD). The root-mean-square (RMS) surface roughness of the n-type Ge layer increased from 0.167 to 14.131 nm when the phosphorus doping concentration was increased from 3 × 10¹⁶ to 3 × 10¹⁹ cm^-3. High-Resolution X-ray Diffraction was used to evaluate the in-plane lattice constants and the tensile strain of the n-type Ge layer as functions of the phosphorus doping concentration. The presence of tensile strain was further confirmed from the Raman measurements, which revealed a strain reduction from 0.071 to 0.065% when the phosphorus doping concentration was increased from 3 × 10¹⁶ to 3 × 10¹⁹ cm^-3. Moreover, a considerable increase in the photocurrent peak energy was observed.