Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] Transparency

On 10/10/2008 06:51 AM, chuck britton wrote:

How does diamond fit into this 'insulator not= large gap

It is the canonical example of a large-gap semiconductor.

A rather large temperature would be required for diamond to carry
an 'injected' charge wouldn't it?


That's just the point. Temperature has got nothing to do with
the motion of /injected/ charge. Once an electron has been injected
into the conduction band, it moves as freely as it would move
through a vacuum.

Temperature has everything to do with the spontaneous production
of non-injected charge, but nothing to do with /injected/ charge.

The theory of this is discussed in Feynman volume III chapter 13
and especially chapter 14.

The relevant experiment can easily be done as an undergrad lab
assignment, since the relevant parameter is band gap divided
by temperature. Silicon at liquid-nitrogen temperature has
essentially the same physics as diamond at room temperature.
Hint: a bipolar transistor is a minority-carrier device, and
therefore doesn't work at all at nitrogen temperature ...
whereas a typical field-effect transistor is a majority-carrier
device and works just fine.