Thermodynamic and kinetic analyses of the Si1-xGex chemical vapor deposition were conducted to study the factors that contribute to the composition of grown thin films as well as their growth rate. The thermodynamic analysis of the Si/Ge/H/Cl system showed that the addition of chlorine to the system directly affects the solid phase Ge content. Chlorine appears to be very effective in retaining silicon in the gas phase by forming a variety of chemical species at all temperatures studied (400 to 800 degrees C), while it retains germanium by forming primarily GeCl2 in the gas phase only at higher temperatures. The effect of chlorine suggests that the composition of the Si1-xGex epitaxial layer can be tuned to a desired value with the addition of a predetermined amount of chlorine to the system as an alternative to changing the ratio of silicon and germanium gaseous sources. In the absence of chlorine, the Si/Ge/H system appears to be more kinetically controlled. A kinetic study was done on the Si/Ge/H system to explain the experimentally observed growth behaviors : a monotonic increase, a monotonic decrease, and a maximum in growth rate with respect to solid phase Ge concentration at low, high, and intermediate temperatures, respectively. A germane-assisted hydrogen desorption path, coupled with the two parallel growth paths from SiH4 and GeH4, where both species compete for the same vacant surface sites, are shown to explain the three distinctive growth rate behaviors observed.