cryogenic CCD operation

[MYPIXEL at aol.com]

Posted to CCD-world:
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**********************jj
Tim,

The subject of interest is called "freeze out". Any solid state text will go
through the gory details (e.g., SZE - Physics of Semiconductor Devices).  CCD
dopants (e.g., n-buried channel) become nonactive below temperatures of about
100 K. That is, there is not sufficient thermal energy to ionize atoms
(phosphorus requires about 0.05 eV to ionize).  We loose depletion and the CCD
potential well at such temperatures and the device stops working. 

We have dunked operating CCDs in liquid nitrogen (- 195 C, 78 K). The CCD
still worked but CTE looked pretty bad (where -100 C operation looked very
good). Shallow traps (silicon impurities) also become more apparent at cold
operating temperatures.

JJ
**********************************jj

 

In a message dated 11/13/98 5:41:15 AM Pacific Standard Time,
Tim.Hardy at hia.nrc.ca writes:

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 I have heard that CCDs cannot be operated at extremely cold 
 temperatures (I'm looking at an application which would operate
 around 30K). Does anyone have any information on this?
 What is the failure mechanism? Has anyone tried it? What is the 
 cutoff temperature?  Is there any published research on this topic?
 
 Thanks for your help,
 
 Tim
 
 
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