A comparison of layered metal-semiconductor optical position sensitive detectors

Position sensitive detectors (PSDs), utilize the lateral photovoltaic effect to produce an electrical output that varies linearly with the position of a light spot incident on a semiconductor junction. In fabricating PSDs, two key elements are optimized: the sensitivity, (mV/increment) and the linearity of the electrical output. Sensitivity is optimized by varying properties of the junction layers, particularly resistivity, while linearity is determined primarily by junction uniformity. In this paper, Schottky barrier PSDs are fabricated from the electron-beam deposition of titanium, tantalum and aluminum on to p-type silicon substrates. Devices were tested under focused broad-band white light and the sensitivities and linearities, for the different metals with varying thicknesses, are compared. Overall, Ti and Ta PSDs performed very well over a large range of film thicknesses, 50 to 2000 Å, while Al was more limited. The best of all the devices fabricated so far was one with 380 Å film of Ti, giving a sensitivity, or output, of 10.62 mV/mm while maintaining excellent linearity and spatial resolution. The best aluminum devices were obtained with a 100 Å film and resulted in a sensitivity of 8.84 mV/mm and a spatial resolution of better than 10 μm. Of the tantalum devices, film thicknesses of around 200 Å produced the highest sensitivities.