The performance of silica-on-silicon planar waveguide devices is highly dependent on the properties of the layers comprising their structure. In this work we have investigated in some detail the properties of doped-silica layers formed by plasma enhanced chemical vapour deposition (PECVD). Parameters such as the refractive index, optical loss, stress and reflow characteristics of borophosphosilicate glass (BPSG) layers have been studied as a function of composition and processing conditions. Using the information gained, we have fabricated arrayed waveguide grating (AWG) demultiplexers and Bragg grating wavelength filter devices. Through careful adjustment of the properties of the top BPSG cladding layers, the performance of these devices, which are highly wavelength and polarization sensitive, can be easily controlled. Correlation of wavelength dependence, optical loss, and polarization dependence of different device designs, with the properties of the top BPSG cladding layer has allowed optimization of these devices and provides invaluable materials and process knowledge for the future use of silica-based layers in these and other photonic device applications.