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Q: Physics ( No Answer,   1 Comment )
Subject: Physics
Category: Science > Physics
Asked by: joyce66-ga
List Price: $25.00
Posted: 11 Oct 2006 04:58 PDT
Expires: 10 Nov 2006 03:58 PST
Question ID: 772603
Which type of Doping (N or P type)would create flow with the greatest
velocity and Why
How does the addition of thermal energy affect the carrier?
There is no answer at this time.

Subject: Re: Physics
From: rawbmobile-ga on 13 Oct 2006 09:43 PDT
Assuming Silicon on 110 substrate; then N type doping will have the
greatest velocity because the effective mass of electrons in Si is
less that the effective mass of Holes in Silicon.  Mobility is related
inversely to the effective mass so a lower mass will have a higher
mobility.  In Si the ratio of mobilities between N and P materials is
roughly in the range of 2 -> 3 :1.  A caveat though, this will have
some dependence upon doping level, see fig 4.11 page 110 of Grove
(physics and technology of semiconductor devices).

The addition of thermal energy ionizes the impurities and allows the
carriers from the ionized impurities to become available in either the
conduction band (for n type) or in the valence band (for P type).  the
proximity of the dopant levels to the band edges in the band diagram
shows that for a dopant to be effective it must be close to the band
edges and thus requires very little energy (in the form of thermal
lattice vibrations) to liberate the electrons/holes.  Proof of this is
in a semiconductor conduction increases as the temperature increases
and the fact that at some temperature the semiconductor will "freeze
out" and not conduct any more.

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