SiO2 dielectric layers are prepared on crystalline Si substrate (n and p types) at 300-degrees-C by two plasma anodic oxidation methods : (a) at higher current densities of 50-80 mA cm-2; (b) by using a very thin (5 cm) aluminium overlayer at low current density (3.8 mA cm-2). The second method is new to the best of our knowledge. Deep level transient spectroscopy (DLTS) and C-V techniques are used to investigate the properties of the oxide-silicon interface. The growth rate of the oxide layer is much higher when a thin Al overlayer is present on the Si wafer, in contrast to Si without Al. Use of an aluminium overlayer leads to a higher interface state density. We demonstrate that, while having a higher density of interface states in metal-oxide-semiconductor structures with a heavily doped semiconductor in comparison with a moderately doped structure, the resulting DLTS signal may be much lower.