2001-02-09
Can you clarify what is meant by "saturation and recovery"?
Answer
Our PSDs are of duo lateral type operating in the photoconductive mode where the generated photocurrent is dividing in sheet resistors on the front and back side of the
device and the current parts are picked up by electrodes.
Saturation for such a detector occurs when the photocurrent has such a magnitude that the voltage drops across the sheet resistors is so large that it equals the reverse
bias across the device. When this happens the pn-junction will be forward biased and the component will cease operating. If bias is gradually diminished the detector will
slow down (capacitance is increasing) and he spatial response will gradually become non linear as the generated charges tend to "modulate the sheet resistors. Detector
responsivity will also gradually decrease.
In a regular photodiode a different kind of saturation occurs. Here the production of photocurrent is saturated and can no longer increase with increased light intensity. This leads to an accumulation of charges in the diode which slows it down. To get rid of these charges after light is turned off you need a recovery time.
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