- #1
CoolDude420
- 201
- 9
Homework Statement
I'm taking a module in Solid State Electronics and in the first chapter we went through energy band diagrams, conduction band, valence band, fermi energy level, forbidden gap, etc. Now in the notes it starts to derive some formulae for electron and hole current densities
Jn = q.n.vn
Jn = electron current density
q = electron charge
n = average number of CB electrons per unit volume, basically the electron concentration
vn = speed with each electron in CB moves in response an applied electric field.
Jp = q.p.vp
Jn = hole current density
q = electron charge, same as hole charge
p= average number of VB holes per unit volume, basically the hole concentration
vp = speed with each hole in CB moves in response an applied electric field.
We were explained EHPs. Basically if a substance gets heated enough so that an electron in the VB has enough energy to cross into the CB and contribute to current flow. Now there is an empty state in the VB, another electron in the VB fills this and contributes to current flow. Now my notes say that "holes also contribute to current flow." I don't understand that. Isn't it the electron that was promoted that is going to contribute to current flow? The hole isn't a particle, its just an empty state. If this is true then shouldn't vp = vn, since electron are the carriers of charge in both cases?