A comparison of layered metal-semiconductor optical position sensitive detectors

Position sensitive detectors, or PSDs, utilise 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 optimised, the sensitivity and the linearity of the electrical output. Sensitivity can be optimised by varying properties of the junction layers, particularly resistivity, while linearity is determined primarily by junction uniformity. In this work Schottky barrier PSDs are fabricated by electron-beam deposition of titanium, tantalum and aluminium 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 were compared Overall, Ti and Ta PSDs performed very well over a range of film thicknesses, 50 Å to 2000 Å while Al was more limited. Ta devices with films of around 50 Å were far superior to the Al equivalent devices. Devices produced from 2000 Å of Ti had high sensitivities of 3.40 mV/mm with nearly perfect linearity, while the equivalent Al devices had markedly lower sensitivities of less than 0.1 mV/mm and were less linear.