# Finding the Saturation Current of a photodiode in Reverse Bias

1. Apr 23, 2007

### r.macdonald

1. The problem statement, all variables and given/known data

I am trying to finish the equation, to compare it against a set of data so I can then find the accuracy of my results in relation to the equation:

I(dark) = I(sat) * e(qV/kT) -1

I have the following data:
Va - the applied (bias) voltage
q
kB - Boltzmann Constant
T the absolute temperature.

2. Relevant equations

as above

3. The attempt at a solution

As the operating temperature of the photodiode increases, two distinctive changes occur in the operating characteristics. The first change is a shift in the Quantum Efficiency due to changes in the radiation absorption of the device. The efficiency decreases in the UV region, while it increases in the IR region, over an increasing operating temperature, effectively making the photodiode more sensitive in the IR region.
The second change, which this investigation highlights, is an exponential increase in dark current, since the electron-hole pairs become excited.

However, to compare the results of this investigation to the equation, I need to obviously know the saturation current of the photodiode. I am using a PN photodiode, so do these types of photodiodes all have a similar saturation current?

Ronald.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Apr 23, 2007

### Staff: Mentor

Welcome to the PF. A couple quick clarifications:

-- remember the parenthesis in your equation: I(dark) = I(sat) * [ e(qV/kT) -1 ]

-- and I believe you mean PIN photodiode, not PN photodiode, correct?

Now, I would think you should be able to find the Isat on the datasheet for your PIN photodiode. Do you have the part number of the diode, or the datasheet already?

3. Apr 23, 2007

### Staff: Mentor

I did a quick google search for pin photodiode Isat datasheet, but didn't get any good sites. Then I used Digikey.com to find a common vendor of PIN photodiodes, and here is a page from them that lists a number of photodetector datasheets near the bottom of the page:

http://www.i-fiberoptics.com/Fiber_optic_led_photodetectors.php