Large Area PIN and Avalanche Photo-diodes

Just a thought - but I think you'd be better off using a smaller (cheap) PIN diode & amplifying a bit harder. I searched around for large-area PINs a while ago for an optical densitometer (covering densities 0.00 to 5.00) - and this is the conclusion I came to. Resulting machine works fine with a BPX65 (1mm²).

Do you have a special need to detect very low light levels?

You could contact Martin Sharratt - mjs@aptechnologies.co.uk - he was very helpful (offers of samples etc).

Light source is 10mm x 10mm surface area crystal to be directly coupled to photodiode. If diode has leakage current of about 10pA at room temperature and capacitance of 10pF to 100pF then )usually operating voltage dependent) and rise time of about 10ns to 30ns and decay time less than 50ns then it will serve the purpose.

Light from crystal is very low and hence > 25% QE is required. I had PIN diodes from Detection Technology with 100pA to 1nA leakage current. These are a bit expensive. Also similar are available from Hamamatsu Japan and are also expensive.

Can you use some optics (as per John Electroman's suggestion)?

This is a fragment of the circuit I used:

The PIN diode exhibits virtually no dark current in this mode (as there's no voltage across it).

Are you looking for speed, sensitivity, both, or what?

Dear JohnDG

This mode for photodiode is like solar cell (good for DC measurement) and capacitance becomes very high. Only by reverse bias pull force on charges depletion region becomes larger and reduces capacitance.

I use in pulse mode and often ~1us pulse width.

High speed and a large sensing area are mutually exclusive in practical terms...

for high speed sensing you need a low capacitance sensor, which means a small junction area etc...

Is there any way you can use an external lense to create a large sensing area from a small sensing chip?

John.

Yes John, I am aware of this basic property. However, I need to have an active area of 10mmx10mm for direct coupling with crystal. Photodiode with 100pF capacitance and 1nA reverse leakage at operating voltages of about 10V to 20V is ideal of QE is about 85% and rise time and decay time <50ns. Wavelength of interest are 400nm to 600nm range.

Avalanche diode is a much better choice as it will provide some good gain also. Now these come as solid state PMT. I wonder if they will be affordable for my application.