Abstract: A process for forming a UV sensitive gallium nitride layer includes a step of depositing a layer of aluminum nitride on which the gallium nitride layer is deposited. Two tests, sheet resistance and photoluminescent response of the gallium nitride layer, allow one to determine that a particular gallium nitride layer produced by the process will have the required response to UV radiation. Either a careful calibration which determines a required length of the aluminum nitride deposition time, or the introduction of silicon into the gallium nitride layer during its deposition, has been found to result in deposit of a gallium nitride layer which has superior UV sensing characteristics.

Abstract: A photoconductor has an active layer of gallium nitride having approximately 10.sup.15 to 5.times.10.sup.15 net donor sites per cubic centimeter and is sensitive to UV radiation. This photoconductor has at least one of a sheet resistance in the approximate range of 10.sup.4 to 5.times.10.sup.6 ohms/unit area and a relatively low level of photoluminescence in the range from about 430-450 nm when excited with light of energy higher than the bandgap energy of 3.4 eV. These criteria tend to define similar semiconductor materials which can form the active layer of an ultraviolet (UV) photodetector having the improved characteristics of a relatively low dark resistance, high sensitivity over at least a range of UV radiation intensity, and decreasing gain with increasing UV radiation.

Abstract: In thin film optical systems including thin film optical waveguides, of such materials as Nb.sub.2 O.sub.5, it is desirable to fabricate thin film lenses. One of the types of lenses which can be made is the step-in-thickness type. This type of thin-film lens can be fabricated by plasma etching through a photoresist mask in such materials as Nb.sub.2 O.sub.5 and Ta.sub.2 O.sub.5. Plasma etching yields an etch wall with smooth steep sides which is important for good quality thin-film lenses; however, the etch rate is too variable for reproducible etch depth based upon etch time, and the bottom of the etch is very rough, causing excessive scattering loss. It has been found that a sandwich-like structure of Nb.sub.2 O.sub.5, TiO.sub.2 and Nb.sub.2 O.sub.5 provides an improved arrangement in that a good control of the etch depth and a smooth flat bottom in the etch areas have been achieved by introducing the layer of TiO.sub.2 as an etch stop.