UV flood recipe ??

[geary%cfa3.DECNET at cfa.harvard.edu]

We have some perhaps interesting results from trying to get stable
QE-pinned performance out of one of our newly-thinned 2K devices. 
We initially tried the "normal" Lesseresque method, with a 20- to
30-minute cadmium flood in pure O2, followed by evacuation, filling
with LN2, and further cadmium illumination until the chip got somewhat
cold (0C or lower).  Bummer!  Could not get good blue response in the
center at all.  In fact, the longer we left the lamp on, the worse
things got.

So, we tried the following: (starting with a very clean dewar,
baked out many hours on the turbo pump at 50C) O2 soak for one hour
with cadmium lamp on, evacuate and immediately turn lamp off, pull
vacuum to 10E-6 (about 2 minutes) and then fill dewar with LN2. 
Everything looks wonderful!!  Very flat, uniform blue response
across the whole chip.

We don't know if a full 1-hour cadmium burn is necessary, but clearly
in this case, we apparently do not want any very intense UV illumina-
tion of the chip under high-vac conditions.  Seems to knock the O
right off the surface, quickly defeating the purpose of the flood.

--J. Geary