The linearity and sensitivity of lateral effect position sensitive devices-an improved geometry

The authors compare the linearity, sensitivity, and resolution of various lateral effect PSDs (position sensitive devices) by computing as a function of vertical position the output voltage produced by a light spot which tracks a horizontal line. In light of the goal of achieving high linearity, high inherent sensitivity, high resolution, and fast response time while maintaining an ability to operate in a fully reverse-biased condition, the authors have designed a new PSD which has a clover geometry. In this lateral effect PSD a pincushion geometry is modified to include an additional four pairs of point contacts located on or near the centers of the curved boundary lines. Each of the contacts at corners is connected to the two nearest point contacts along the boundary. It is shown that the clover PSD is nearly as linear as the duolateral PSD while holding similar position resolution, but has all of the contacts on a single side of the p-n junction so that the dark current is lower, response time is faster, reverse-bias can be applied more easily, and fabrication cost is lower. The clover inherent sensitivity is five times that of the pincushion and more than half that of the duolateral duoaxis PSD.