processing conditions by which the a si film is created however while hydrogenated a si may provide better transparency in the near infrared than pure a si pure a si may be processed more easily pure a si may also have a larger thermal stability then that of hydrogenated a si further such a si films may be formed using pecvd to have properties different from those of pure a si for example a n 2 based pecvd formation of a si may form an amorphous silicon nitride a sin y silicon nitrides may generally be used for a myriad of purposes in a variety of compound semi conductor devices such uses including for example surface passivation interlayer elements and capacitor dielectrics as with any optics design optical loss mechanisms such as optical absorption and optical scattering losses are of concern in the above referenced waveguide embodiments scattering loss is common to all optical waveguide designs and is generally caused by roughness at the interfaces between core and clad as well as by any inhomogeneities in the deposited film absorptive loss may be primarily dominated by optical absorption that excites stretching vibrational modes of atomic bonds between hydrogen or deuterium and heavier elements present in the deposited film such an absorptive loss may depend heavily on the amount of hydrogen or deuterium in the film and or on the particular optical wavelength or wavelengths propagating in the waveguide absorptive loss may particularly be an issue for optical wavelengths near the primary or lower order overtones of a hydrogen u2014 or deuterium u2014 related vibrational stretching mode the strength of a stretching vibrational mode absorption feature.