We report the growth and structural and optoelectronic properties of films of hydrogenated amorphous silicon (a-Si:Hi and microcrystalline silicon (mu c-Si:H). The films were grown by combining very high frequency (80 MHz) excitation of the glow discharge with the addition of dichlorosilane (SiH2Cl2) to the source gas of silane (SiH4) and hydrogen (H-2). While the transition from a-Si:H to mu c-Si:H is achieved by H-2 dilution, the film properties are affected by the addition of SiH2Cl2. Adding SiH2Cl2 raises the I-I content of mu c-Si:H and reduces the electrical conductivity (at 300 K) by 2-6 orders of magnitude, in comparison to mu c-Si:H deposited from SiH4 and H-2 alone. A most important result is the growth of thin-film transistor quality mu c-Si:H at the relatively low substrate temperature of 230 degrees C,