Category: Science > Physics
Asked by: joyce66-ga
List Price: $25.00
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?
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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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