Large-ish area flat photodiode for NIR (1092 nm)

David Nadlinger wrote in news:qdi0ui$ams$ snipped-for-privacy@news.ox.ac.uk:

Perhaps an IR resistor bolometer? They have windows in front so only let pass a specific band. Not a diode, but still could be "read", depending on your need.

How about a small lens, focus to an optical fiber. There are many fast, affordable fiber detectors. E.g., QPhotonics QPDI-80, InGaAs, to 2GHz, $109. I have special RIS-617 versions for these babies.

Several are installed in our advanced AFM systems. Free PCBs if you want to experiment.

--
 Thanks, 
    - Win

David,

I've had like problems with detecting short laser pulses: a long tail of many usecs. After some testing I discovered that the area _outside_ the ring around the active area was the cause: any electrons generated there would, after the pulse, slowly drift into the active area causing the tail. First solution: hacksaw the case, and paint the ring and the area outside it black. Problem solved. Second solution for production: a diaphragm covering the inactive area.

Regards, Arie de Muijnck

I don't know what you mean by 'sensibly'. Silicon will work at some level at 1092 nm, and is *dramatically* cheaper than InGaAs, so there's a pretty steep price/performance tradeoff around there. A silicon PD with a heater nearby might save you some dough.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

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OH good, that was my guess too, an edge effect. Try a mask with some black electrical tape. (That's what I did.)

Arie, it was someone here(SED) who warned me of this effect, was it you?

George H.

Luna SD039-151-001 is one option if you can get them. Of those Hamamatsu ones I selected G13176, which at least for us is about 40% lower cost than the ceramic package G11193.

--
mikko

Some years ago I already described this effect in this group, don't know to whom.

Arie.

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Well then thanks again for that! I see this effect every time I use blinking LED's to test photodiode amps. I never looked for any wavelength dependence, maybe next time I'm testing.

George H.

Great suggestion, thanks ? I wasn't really aware of Luna Inc. Unfortunately, it seems they no longer manufacture that particular part, at least there doesn't seem to be any stock at DigiKey or any of the usual places. I've contacted them; maybe I'll get lucky.

Thanks, good to know.

Best, David

Thanks for the hint ? unfortunately, the spatial distribution doesn't seem to be the problem in this case.

Masking off everything but a central ~2.5 mm x 2 mm area with electrical tape didn't change the response at all (apart from a small decrease in the overall amplitude).

small edge effects are rather unlikely to be the cause, I suppose.

? David

It seems I might be; apparently Luna were bought by OSI last year and are now Advanced Photonix.

? David

No, that rules out the edge effect as major contributor. In my case it was about 10% of the amplitude.

You do have _stiff_ biasing? Maybe amplifier related causes? A diagram with some signal level indications I could review.

Arie

The very same photodiode module shows clean

didn't

Huh, Some shallow impurity (doping) in the PD? Do you have access to a spectrometer? You can turn it monochromator* and look at the response .

Maybe some interference fringes from the coating? If you put a little squeeze on it (maybe an alligator clip) does it change?

George H.

*weird spelling, my first guess had a meter on the end... maybe we could all agree to call it a monochrometer, from now on. :^)

Sounds like you haven't depleted the PD all the way to the back contact. That causes diffusion tails selectively at longer wavelengths. If you crank up the bias, it's common to see gradual improvement followed by a dramatic speed-up when the die is fully depleted.

This isn't usually possible with PN diodes, but it usually is with PINs.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Yes, seems like that is what must be happening. I am already biasing the diode at 14 V, so didn't expect to see this, but then again, the S6775 is probably rather wide (which matches the 35 V abs. max rating).

Would the amount of charges generated outside the depletion region grow more or less proportional to the reduction in QE/absorption coefficient near the cut-off? Is there a way to estimate the punch-through voltage from looking at typical datasheet capacitance/dark current diagrams? I really need to have a more principled look at detector physics one of these days.

I'll try to get some step response vs. reverse bias data next week, at a few different wavelengths.

? David

In this instance, I have some 35 of these detectors on a single optical table, so I wanted to avoid the extra complexity that comes with fibre-coupling. The beam sampler modules use large-area photodiodes and integrate PCBs as well as beamsplitters/filters to reduce alignment complexity. (There are already ?40 fibre collimators on that table to worry about.)

Many thanks for this very kind offer! It was also interesting to flip through your designs. Mine are not entirely dissimilar, which might have something to do with the fact that I am using AoE as my monitor stand (those references to 3.x in the main text sure were tantalizing when first looking into it ? I am definitely looking forward to the x-chapters release).

Did you ever look at negative output swing on the ADA4817? I am using it with positive photodiode bias on said boards, and measuring only ? -3.6

but reproducible in isolation (>> 1 k? output load) although all samples I tried were from the same reel. Had I known this, I would have chosen different supplies. The joys of iterative design?

? David

It depends on the details of the doping profile. One common method for making ohmic contacts is to crank up the local dopant density till the band gap goes away, in which case you're never going to get it fully depleted.

Not that I know of. Photodiode datasheets are almost as bad as diode laser datasheets.

They never, ever tell you about the series resistance, which is a crucial parameter for low-noise photoreceiver design.

I'd be interested to see them.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Yes, that's pretty annoying. I have some VNA S11 traces of the S6775 vs. reverse bias, but they are a bit harder to interpret than I'd hoped. The real part of the impedance at 10 MHz ranges from 110 ? at 66 mV bias to

80 ? at 15 V. Makes sense; the width of the undepleted region gets smaller. However, there is a resonance around 410 MHz that doesn't move with bias voltage ? its residual (real) resistance at 66 mV bias is 15.5 ? and reduces slightly to 13 ? at 15 V.

This very much doesn't look like a current source with shunt C and series/shunt R. Just soldering a capacitor on legs into the production version of my frontend PCB would probably be the easiest way of figuring out the (noise-)equivalent series resistance for later reference.

I wish I had the time to buy a few of every (sort-of-)large-area photodiode out there and compile a database of parasitics as a function of reverse bias. This would be seriously useful.

? David