Low temperature epitaxy of Si and Si1−xGex by utrahigh vacuum-chemical molecular epitaxy

Abstract

Pure Si2H6 and GeH4 are used to grow Si and Si1−xGex epilayers at 550 °C by ultrahigh vacuum-chemical molecular epitaxy. 0.1% B2H6 and 100 ppm PH3 diluted in H2 are used as the p- and n-type dopant gases in Si/Si1−xGex epitaxy. The Ge mole fraction x and the growth rate of Si1−xGex epilayers show very strong dependence on the total source gas flow rate ([GeH4]+[Si2H6]) and the source gas ratio ([GeH4]/[GeH4]+[Si2H6]). The results can be explained by the relationships of the source fluxes, relative incorporation efficiency at activated surface sites, and hydrogen desorption under different growth conditions. The boron concentration of Si1−xGex increases with increasing GeH4 flow rate by keeping Si2H6 and B2H6 flow rates constant. It may be due to the increase of the surface sites which is caused by the increase of the hydrogen desorption rate when a higher Ge mole fraction epilayer is grown. The phosphorus concentrations of Si and Si1−xGex show different behavior with PH3 flux at higher PH3 flow rates while one increases linearly and the other becomes saturated, respectively. These results can be explained by a model based on the different levels of the effects of phosphorus blocking of surface-activated sites between Si and Si1−xGex epilayers. This effect can also be used to explain the fact that a smaller decrease in the growth rates of Si1−xGex epilayers occurs at a higher PH3 flow rate.