need Avalanche photodiode

Hello,
In order to use in our graduation project, we need an avalanche photodiode.We searched on the internet but we found out that APD's are way too expensive for our budget (mostly over 1000S). Do you know whether there are cheaper APDs (or another alternative) available, also can we find APDs in other second-hand, unused devices, where we can acquire them in a cheaper way?
Thanks for your help

APDs are expensive, but I don't think I have paid more than ￡50 or ￡100 for one. Have you looked at Hamamatsu and Silicon Sensor? What size are you looking for? Where in the world are you?

Keith

We checked the ones from Hamamatsu and from the Advanced Photonics. Hamamatsu does not give prices in its own web site, but from other sites we found prices on the order of 1000 Dollars, but these were in a whole module.
we need it to use in a frequency domain near infrared imaging system. we need to sense light as low as 10pW modulated around 100-150MHz. We will use it as a sensor on human head, so it shouldn't be too big. In terms of the sensing area it needs to be less than 1cm2.
but regular PIN photodiodes seem to be not suitable. do you have any suggestions?

You need to be looking at simple APDs and design your own electronics. Modules will be expensive - they can be quite sophisticated with programmable temperature compensation. If you just need something for experimentation a box of a couple of dozen PP3 batteries and a trim pot will suffice. You can snap the batteries together to get the voltage you need and put a potentiometer across the top one for fine adjustment. Remember to include decoupling capacitors and a current limit resistor.

You will need some sort of transimpedance amplifier and there are a few around or you can make them with an opamp. If you would prefer a ready made solution Silicon Sensor do an APD with transimpedance amplifier in a single package for around ￡120, from memory.

With regards to size a 0.2mm diameter device will be cheaper than a 0.5mm device and so on. Small devices need very good optics though.

Keith