Hydrogenated amorphous silicon samples have been deposited by plasma-enhanced chemical-vapor deposition, using a square-wave amplitude-modulated radio-frequency excitation. In this article it will be shown that a combination of amplitude modulation and low gas flows improves the gas-utilization efficiency by a considerable amount. Using a conventional 50 MHz SiH4/H-2 plasma with gas flows of 30 sccm, both for SiH4 and H-2 at a pressure of 20 Pa, the gas-utilization efficiency is about 8%. It increases up to 50%. by modulating the amplitude of the radio-frequency excitation signal and reducing both gas flows to 10 sccm, keeping the pressure constant. In this case, the deposition rate amounted to 0.55 nm/s. The combination of amplitude modulation and gas flow reduction gives rise to sufficient ion bombardment and hydrogen dilution at low flows. Device-quality optoelectronic properties are obtained under these conditions. The refractive index at 2 eV is about 4.25 and the microstructure parameter has a value around 0.02. The electrical properties were also appropriate for solar cell application. The photo-to-dark-conductivity ratio varied between 10(5) and 10(7). The material exhibited a low defect density which is in the order of 10(15)-10(16) cm(-3). The Urbach energy amounted to 52 meV on the average. (C) 2003 American Vacuum Society.