Photodiode problem: higher currents in photoconductive than in photovoltaic mode

Nov 29, 2006 4 Replies
U

Hi,



I have a silicon photodiode and I am trying to characterize it. When I measured the currents generated in photovoltaic mode (PV) of operation (without applying a bias) and in photoconductive (PC) mode of operation (applying a 5V reverse bias voltage), I noticed that the Signal to noise (dark current) was much better for the photoconductive mode of operation.



Now, everywhere that I have read suggests that in the Photovoltaic mode of operation the circuit should be much more sensitive.



For examlple, in photovoltaic mode at some optical power, I get 0.044 nA of current being generated with a dark current of about 0.003 nA. In the photoconductive mode of operation, I get 3.98 nA of current generated when biased at 5V with a dark current (light off) of about the same 0.003 nA.



Also, shouldn't the dark current in photoconductive mode of operation increase with the applied reverse bias voltage? However, I noticed a constant dark current while varying my reverse bias voltage.



Also, I am using a picoammeter for my measurements.



Any help or suggestions would be greatly appreciated.



Thanks.



Vote
Twitter Facebook LinkedIn
S

You might try to increase the voltage to the avalance voltage, at which it starts to behave like a photo- multiplier. However, it might also break your cell. To avoid that use a series resistor to limit the max. current.(And dont use an expensive cell).

Vote
Twitter Facebook LinkedIn
R

The sensitivity should be the same, so long as it is not saturating in photovoltaic mode.

What resistance is on the diode in the photovoltaic measurement? My first thought was that it is saturating (too high a resistance). That generally means the diode voltage is at least 0.2 or 0.3 volts, which for 0.044 nA would mean a whopping several-Gigohm resistance.

A dark photodiode behaves pretty much like a regular diode. The reverse current (dark current) is fairly constant, increasing only slightly, so long as you're below the reverse breakdown point.

Vote
Twitter Facebook LinkedIn
U

should be the same, so long as it is not saturating in

measurement? My

photodiode behaves pretty much like a regular diode. The

Vote
Twitter Facebook LinkedIn
R

Yes, most definately. It depends very strongly upon what resistance value the diode is driving. That particular information would enable me to help you better.

Regards,

Mark

Vote
Twitter Facebook LinkedIn

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required