Alternating cyclic (AC), selective area deposition of Si1-xGex thin and thick films, 0.1 to 3.5 mu m ria the reaction of SiCl4, GeCl4, and fit using Ar as a carrier gas, was carried out in a hot-H all, LOW pressure epitaxial reactor, using oxide masked silicon wafers. The AC process is based on the existence of an embedded disproportionation reaction within the overall deposition chemistry, which provides an effective mechanism for preventing the formation of nuclei in the areas where deposition is not desired. This disproportionation reaction is made dominant cyclically, by pulsing the hydrogen on and off periodically, in order to eliminate incipient nucleation. Experiments were carried out over a large portion of the available parameter space, as determined by extensive thermodynamic analyses, using a reference non-AC process as a control, and comparing the results with different AC frequencies. The [GeCl4/(SiCl4 + GeCl4)] mole fractions used were 0.0012, 0.0025, 0.005, 0.01, 0.02, 0.03, and 0.05, the temperature was varied from 700 to 950 degrees C, and the Ar/H-2 ratio varied from 1 to 9. The range of alloy composition deposited was from 0 to 30 mol %, Cc. Total gas now rate was varied from 2 standard liters per min (slpm) to 20 slpm to modulate gas hydrodynamics. To varying degrees, various experimental conditions influenced the tendency for formation of spurious nuclei on the oxide surface. However, under all conditions, the AC technique was capable of preventing the formation of spurious nuclei on the oxide, guaranteeing essentially 100% selectivity control, for both nonimplanted wafers and ion-implanted wafers.