The deposition of in situ-doped n- and p-type polycrystalline Si1-xGex ( 0 <= x < 0.5 ) films by low pressure chemical vapor deposition ( LPCVD ) at low temperature ( 425 C ) is characterized. The results demonstrate the dominance of surface reaction effects for low temperature deposition. For n- type films, Si2H6 is required to avoid phosphorus ( P ) poisoning effects and to achieve controllable deposition. P incorporation increases with Ge concentration within the as-deposited films, likely due to P-P dimer suppression by GeH4. For p-type films, SiH4 is the preferred Si precursor gas because it yields over one order of magnitude higher B concentration as compared with Si2H6. This difference is attributed to the differences in reactive sticking coefficient ( RSC ) and in the amount of Si produced by the precursor gas. B incorporation decreases with increasing Ge concentration within the as-deposited films, due to competition for adsorption sites during deposition. GeH4 depletion was observed to affect the dependence of Ge composition on GeH4 partial pressure, but not the deposition rate, which has a greater dependence on the RSC. (c) 2007 The Electrochemical Society.