Position sensitive device
On a laminar semiconductor, a so-called PIN diode is exposed to a tiny spot of light.
The dependence of local measurement on form and size of the light spot as well as the nonlinear connection are a disadvantage that can be partly compensated by special electrode shapes.
A 2-D tetra-lateral PSD is capable of providing continuous position measurement of the incident light spot in 2-D.
It consists of a single square PIN diode with a resistive layer.
When there is an incident light on the active area of the sensor, photocurrents are generated and collected from four electrodes placed along each side of the square near the boundary.
The incident light position can be estimated based on currents collected from the electrodes: and The 2-D tetra-lateral PSD has the advantages of fast response, much lower dark current, easy bias application and lower fabrication cost.
Its measurement accuracy and resolution is independent of the spot shape and size unlike the quadrant detector which could be easily changed by air turbulence.
To reduce the nonlinearity of 2-D PSD, a new set of formulae have been proposed to estimate the incident light position (Song Cui, Yeng Chai Soh：Linearity indices and linearity improvement of 2-D tetra-lateral position sensitive detector.
The position estimation results obtained by this set of formulae are simulated below.
We assume the light spot is moving in steps in both directions and we plot position estimates on a 2-D plane.
Detailed simulations and experiment results can be found in S. Cui's paper.
The most common sensor applications with a sampling rate of less than 1000 Hz are CCD or CMOS cameras.
The position of the light spot can be computed with the methods of photogrammetry directly from the brightness distribution.
From all columns and all lines the one element that is brighter than a given threshold value is the average value of the coordinates computed of the light spot.
More recent hybrid structures based on PEDOT:PSS/n-Si heterojunction exhibit ultrahigh sensitivity and excellent linearity.
