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Why is BOTH the electron & hole drift velocity positive? 
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#1
Oct1512, 02:05 AM

P: 12

Good Morning,
The equations under investigation: Electrons: J = enμE + eD(dn/dx) Holes: J = epμE  eD(dp/dx) n or p = concentration of electrons or holes respectively D = diffusion constant μ = mobility The question in mind is as follows: If holes are traveling in the direction on conventional current, then shouldn't the drift velocity for holes be fully negative, i.e. epμE  eD(dp/dx)? I understand by definition that, μ = mobility, is the absolute value of drift velocity (speed) over the electric field hence the direction is lost in the process (or is the same for both a hole and an electron). Therefore, shouldn't the expression for holes written above also technically factor in a negative sign corresponding to the hole drift 'velocity' part of the equation? Please dispel my confusion lest more holes puncture brain. 


#2
Oct1512, 03:23 AM

Sci Advisor
P: 3,593

No, mobility is proportional to the inverse of the effective mass. However, at the top of the valence band, the effective mass of an electron is negative and they have a negative mobility. Hence the holes have a positive mobility.



#3
Oct1512, 08:44 AM

P: 315

Oz Alikhan,
Ratch 


#4
Oct1612, 09:31 AM

P: 661

Why is BOTH the electron & hole drift velocity positive?
It's because holes have a positive charge, so the same direction of electric field acts in the opposite direction than on electrons.



#5
Oct1612, 10:53 AM

P: 315

Enthalpy,
To whom are you addressing your comments, and what question are you answering? Ratch 


#6
Oct1612, 11:46 AM

P: 12




#7
Oct1612, 11:51 AM

P: 12




#8
Oct1612, 01:18 PM

P: 315

Oz Alikhan,
Ratch 


#9
Oct1812, 02:53 PM

P: 661




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