[SI-LIST] Re: si-list Digest V5 #210
- From: Dimiter Popoff <dp@xxxxxxxxxxx>
- To: <arpad.muranyi@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 17 May 2005 3:15:42 +0300
I believe I can add some example based data to that.
In high-resolution gamma spectroscopy the detector is a Ge
crystal, liquid nitrogen cooled, and biased by 2 to 5 kV.
The charge each event (a gamma quantum hitting the crystal) results
into is the signal of interest; nowadays it is processed with
14 bit precision.
In order to do that, the preamplifier first stage is the lowest
noise JFET one can get, cooled down to about -90 to -100 C, which
yields the achievable in terms of noise performance.
Thus Si is known to operate well at about -100 C; the Ge crystal
works at liquid nitrogen, the charge each photon hit produces
being collected in a matter of nanoseconds (with big crystals
this can go into hundreds of nanoseconds varying with
the point/direction of the impact etc., it is real fun to
filter out the precise charge value...).
Dimiter
------------------------------------------------------
Dimiter Popoff Transgalactic Instruments
http://www.tgi-sci.com
------------------------------------------------------
> From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
> To: <arpad.muranyi@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
> Subject: [SI-LIST] Re: si-list Digest V5 #210
> Date: Mon, 16 May 2005 16:51:44 -0700
>
> From the Handbook of Physics
>
> Semiconductors..."At absolute zero the ideal structure is an insulator. At
> elevated temperatures, electrons can be thermally excited from the valence
> band to the conduction band, giving intrinsic conductivity from equal number
> of conduction electrons and holes....."
>
> Tom Dagostino
> Teraspeed Labs
> 13610 SW Harness Lane
> Beaverton, OR 97008
> 503-430-1065
> http://www.teraspeed.com
> tom@xxxxxxxxxxxxx
>
> Teraspeed Consulting Group LLC
> 121 North River Drive
> Narragansett, RI 02882
> 401-284-1827
>
> Teraspeed is the registered service mark of
> Teraspeed Consulting Group LLC
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Muranyi, Arpad
> Sent: Monday, May 16, 2005 4:02 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: si-list Digest V5 #210
>
>
> Thanks for the two responses to my question from Lynne, and Chris.
>
> Let me recap the thread, and restate my question, because I don't
> feel that it was completely answered yet.
>
> The thread started with the question on what happens with silicon
> semiconductor devices below -55 C. A response came back to say
> that at 77 K silicon will act as an insulator. Someone else
> responded that this was not the case. Then the previous writer
> corrected themselves saying that they were referring to pure
> silicon being an insulator at such low temperatures.
>
> This is when I asked my question. I may have read too much into
> the thread, but it seemed to imply that PURE silicon is an insulator
> at those low temperatures, but less of an insulator at higher
> temperatures, such as room temperature. This surprised me.
>
> I am certainly not an expert in this area, but I thought that PURE
> silicon was an insulator because the way its crystal structure is
> built. There are no free electrons in it. I don't see how temperature
> can effect its conductance, unless something drastic starts happening
> in the crystal structure. Chris' response to my question pretty
> much confirmed this, although I would be curious to hear more about
> what those mechanisms are which can do that.
>
> Lynne's response seems to apply to doped silicon. I agree the mobility
> of those carriers can be influenced by temperature a great deal, but
> again, I was curious about PURE silicon, since that's what my first
> response (question) was triggered by.
>
> So is my recollection correct that at normal room temperatures and
> thereabout, PURE silicon would still be a perfect insulator, or does
> it have to be cooled way down (say to 77 K) to become an insulator?
>
> Thanks,
>
> Arpad
> -----------------------------------------------------------------------
> -----Original Message-----
> From: lgreen [mailto:lgreen22@xxxxxxxxxxxxxx]=20
> Sent: Monday, May 16, 2005 3:28 PM
> To: Christopher.Jakubiec@xxxxxxxxxxxx; Muranyi, Arpad; =
> si-list@xxxxxxxxxxxxx
> Subject: RE: [SI-LIST] Re: si-list Digest V5 #210
>
> Hi, Arpad,
>
> Silicon bulk resistivity (and conductivity) is strongly temperature
> dependent. At room temperature, the resistivity is higher than metals, =
> but
> too high to use it as a good insulator (hence the name semi-conductor).
> Resistivity is also very sensitive to impurities, with the usual =
> impurities
> leading to a slightly n-type material in silicon.
>
> At "low" doping (about 10-100x the impurity level), the resistivity =
> becomes
> both lower and less sensitive to temperature. It also becomes possible =
> to
> predictably control the built-in junction potential.
>
> At very high temperatures, of course, the thermally generated carriers =
> can
> dominate over the doping. But that is normally outside the operating =
> range,
> unless you get a local high current density.
>
> - Lynne
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
> On
> Behalf Of Christopher.Jakubiec@xxxxxxxxxxxx
> Sent: Monday, May 16, 2005 2:17 PM
> To: arpad.muranyi@xxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: si-list Digest V5 #210
>
> Arpad,
>
> I agree with your statement to an extent. Current flow in silicon is
> related to the amount of free carriers (either holes or electrons) that =
> are
> available to participate. Free carriers can be induced both by means of
> impurity doping in the silicon, and electron/hole pairs can be thermally
> generated even in pure silicon (although not normally for a practical
> purpose).
>
> Regards,
>
> Chris
> Infineon Technologies
> =3D20
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Muranyi, Arpad
> Sent: Monday, May 16, 2005 2:15 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: si-list Digest V5 #210
>
>
> Jut to clarify things I would like to ask a question:
>
> My understanding was that pure silicon is not conductive, not even at =
> room
> temperature(?). The doping is what freezes up some electrons to make it
> conductive. How does this relate to temperature?
>
> Thanks,
>
> Arpad
> -------------------------------------------------------------------------=
> --
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> =3D3D On Behalf Of Daniel Chow
> Sent: Monday, May 16, 2005 10:44 AM
> To: John Zasio
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: si-list Digest V5 #210
>
> My bad.
>
> My statement was true for pure silicon.
>
> Heavy doping significantly changes the properties of silicon.
>
>
>
> -----Original Message-----
> From: John Zasio [mailto:zasio@xxxxxxxxxxxxxxxxxxx]=3D3D3D20
> Sent: Monday, May 16, 2005 10:25 AM
> To: Daniel Chow
> Cc: si-list@xxxxxxxxxxxxx
> Subject: Re: [SI-LIST] Re: si-list Digest V5 #210
>
> Daniel,
>
> Silicon devices do work and work well at liquid nitrogen =3D3D
> temperatures.=3D3D3D20 CMOS devices will run at two to three times =
> faster than
> at room temperature.
>
> In the mid 80s ETA Systems shipped a CMOS Supercomputer cooled by liquid
>
> nitrogen. Although the product was not a commercial success, =
> the=3D3D3D20
> technology worked very well.
>
> John Zasio
>
> Daniel Chow wrote:
>
> >Jon,
> >
> >No silicon part will work at liquid nitrogen temperatures (77 Kelvin).
> >
> >Silicon is an insulator at that temperature. The charge carriers are
> >"frozen out" at low temperatures.
> >
> >Please refer to Chapter 8 of "Solid State Physics" by Charles Kittel
> for more details.
> >
> >Thanks!
>
> >Daniel Chow, Ph.D.
> >Sr. Product Engineer
> >ALTERA
> >Office: (408) 544-8100
> >Fax: (408) 544-7602
> >Email: dchow@xxxxxxxxxx=3D20
> ------------------------------------------------------------------
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