Could you suggest if it's possible to effectively use SiGe/GaAs RF MMIC (which have 50 Ohm input impedance) as first stage of photodiode amplifier? 

The idea is to reverse bias diode from some +50V, and connect it directly to MMIC input, so that photodiode is loaded to MMIC's internal 50 Ohm termination. 50 Ohm might be quite low value though. 

I am mostly worried about noise figure, frequency range is 1-100Mhz (maybe even 1-4Ghz???). Final target is to detect individual photons (with some probability) or dozens of photons (photo-diode QE is 30-70%).

I understand that typically one would need transimpedance amplifier for this job, but using common off-the-shelf SiGe/GaAs part in my dreams might yield lower noise...

PS. I understand that silicon photomultipliers / APD might be more useful here, but they are prohibitively expensive.

PPS: Parts I look at are :  

[Mini-circuits MAR-6 2GHz 3dB NF](http://194.75.38.69/pdfs/MAR-6+.pdf)  

[Mini-circuits PSA4-5043+ 4GHz <1dB NF](http://194.75.38.69/pdfs/PSA4-5043+.pdf)