Phosphorus doping effect on $Si_{0.8}Ge_{0.2}$ epitaxial growth by LPCVD

저압 CVD에 의한 $Si_{0.8}Ge_{0.2}$ epitaxial growth에 대한 Phosphorus doping 효과

We have studied the epitaxial growth and electrical properties of $Si_{0.8}Ge_{0.2}$, films on Si substrates at $550^{\circ}C$ by LPCVD. In a low $PH_3$, partial pressure region such as below 1.25 mPa, the phosphorus doping concentration increased proportionally with increasing $PH_3$ partial pressure while the deposition rate and the Ge fraction x were constant. In a higher $PH_3$ partial pressure region, the phosphorus doping concentration and the deposition rate decreased, while the Ge fraction slightly increased. The dependence of P incorporation rate on the $PH_3$ partial pressure was similar to the phosphorus doping concentration. According to test results, it suggests that high surface coverage of phosphorus atoms suppress both the $SiH_4$ adsorption/reaction and the $GeH_4$ adsorption/reaction on the surfaces, and the effect is more stronger on $SiH_4$ than on $GeH_4$. In a higher $PH_3$ partial pressure region, the deposition is largely controlled by surface coverage effect of phosphorus atoms.