Diamond-like carbon (DLC) films deposited by the microwave plasma CVD technique under varying bias voltages are investigated using atomic force microscopy (AFM) and spectroscopic ellipsometry. AFM investigations are used to study the surface morphology, while the ellipsometric studies are used to study the variation in the density and the sp³ _/ sp² ratio of these films. The surface morphology, density and sp³ _/ sp² ratio of these films are related to each other and follow the sub-plantation model. The DLC films deposited at low bias voltages (–100V to –300 V) show an increase in the density with increases in bias voltage. The films deposited in high bias voltage range (approx. –800V to –1400 V), however, show saturation in their density. The sp³ / sp² ratio is also found to increase with increase in bias voltage, but only up to a certain limit (approx.–1000V) beyond which its value decreases.