SITe QE values ??

[Paul Jorden]

John, & others,

> We are looking to buy a goodly number of large CCDs in the very
> near future.  One of the stumbling blocks may be our QE desires,
> summarized below:
> Recently, SITe has informed us that they may perhaps be able to
> comply with the above requirements.  My question:
> Does anyone out there have actual QE measurements of thinned SITe
> devices that approach the above.  I certainly have never seen anything
> approaching these values, but perhaps someone has some unpublished
> measurements.
> Comments would be welcomed.  JG.

I've compiled my table, with John's desires, and three chips measured at RGO at 
cryogenic temperatures. I've added some extra wavelength points also.
Thr RGO-measured chips are- a recent EEV CCD42 sample chip, a 5-yr old standard 
TK1024, a recent Lesser-thinned 2k3eb Loral chip (2-layer AR).

WAVELENGTH    	JG desire       RGO-QE (EEV42)	RGO-QE (TK1024)	RGO-Lesser

330  		50%		32		19		72
350             		38             	26		73
400     	85		65		54		71
500             		85		63		80
600     	85		86		69		88
700     	85		73		69		90
800     	75		51		56		81
900     	50		25		29		55
1000                  		5 		7		21

Firstly no chips have matched all of JG's desires.
As we know only the Lesser process has demonstrated the exceptional UV figures; 
but even his current 2-layer coatings do not seem able to provide 85% at 400nm. 
I suspect that a coating that gave 85% at 400nm would fall off more into the 
red, and not provide the 800/900nm desired response. Any comments Mike??

It is also fairly clear that the chip cannot be made too thin, if it is to have 
a high red response.  In this case, many chips with normal resistivity silicon 
(20-100 ohm) are not fully depleted, and will suffer poor blue MTF. This is seen 
in standard Lesser-thinned chips. I think you know this John, but I'm 
broadcasting this message also..

I recall considering the Gemini CCD specs, and I think they had the same 
problem- ie looking for high UV and far-red response, as well as high peak 
figures. My guess is Mike Lesser could get closest. However, a commercial 
supplier (like SITe or EEV) could offer better quality devices reliably, but 
surely would struggle with the 330nm response; and if they managed to achieve 
it, I don't think they could offer good 900nm response at present!

I've seen Alistair's recent figures; my comment is that the SITe UV figures look 
pretty good, but I'd always prefer to know cryogenic values.
Good luck. I'll be interested in any comments from others.

Regards, Paul
-------------------------------------------------------------------
E-mail:  prj at ast.cam.ac.uk         Machine: Kria.ast.cam.ac.uk
Royal Greenwich Observatory, Madingley Road, Cambridge, CB3 0EZ, UK.
Phone: +44 (0) 1223- 374000  \direct phone- 374811 \RGO Fax- 374700