High resistivity CCDs

[Paul.Jorden at eev.com]

Posted to CCD-world:
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Hi Richard, and everyone,

I'd like to add to the discussion about deep depletion devices  I'm glad you started it again  Also, your 
web-links to LBL/Lick papers on these devices are very helpful.

>  These devices promise some really spectacular 
performance because they are 300um thick and are 
sensitive throughout that entire volume. This 
means they have superior red response and NO 
FRINGING out to 1000nm

>  Thinning is not required, so the expensive and
difficult thinning processing is eliminated. Holes, 
instead of electons, are the signal carriers so 
special backside treatments to enhance QE aren't
needed. This means they have good blue response too.

Perhaps you should repeat that you are using n-type 
Silicon (cf the p-type material that is normally used
for CCDs).  Of course, high resitivity is also possible
with p-type, although the properties are somewhat different.

>  No design is perfect and even these CCDs have their limitations.  (Some are spelled out in the papers found
 at the home page.)

I recognise the advantages, and would hope that EEV 
could make more such variants in the future.  I would 
be interested in seeing a good summary of the pros 
and cons of these devices- do you know of one?

Of course the high red sensitivity can be invaluable 
for most astronomy applications.  I'm interested in 
trying to gauge the value, and then weigh up the 
merits of the device against the disadvantages, as I 
guess you and others are.  Let's discuss the two 
main applications-

(a) direct imaging.  High QE is especially useful for 
good S/N.  With high resistivity, the depletion well 
would be expected to collapse more quickly as charge collects.  Do you have any figures on full-well 
capacity?

(b) Spectroscopy.  An improvement in far-red throughput really helps. I guess most spectrographs have ~ f/3 cameras.  Do you know how good a spatial resolution (ie spectral resolution) can be achieved?  I still can't see how
a 300 um thick device can be used with effectively a 
large far red depth of focus.  It seems to me that 
in this application spectrographs are normally.

focussed with a line width of order one pixel (~15 um), 
and minimum broadening or scattering would be important.

Also, how do you find general quality of your deep 
depletion devices- eg. cosmetics, dark current, blemishes 
or spots?  I realise that it is early days yet, but 
any info is valuable.

Does anyone have any comments on these specific concerns, 
or any others?

Let me say that I still feel the deep depletion concept 
is valuable, and I'd like to see it explored....

Best Regards,
Paul
_______________________________________________________________
Dr Paul Jorden,  CCD Applications, EEV
Waterhouse Lane, Chelmsford, Essex, CM1 2QU, UK
Tel:      44 (0) 1245 -453458 (direct), -493493 (switchboard)
Fax:      44 (0) 1245 453224
see also:-     http://www.ccd.eev.com/


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