Week 11 Electrons, Holes & Effective Mass

Question 1

how does mass change from the Free Electron Model to the NFEM/TBM

Answer 1

the energy is modified by lattice interactions and the mass is no longer well defined

Question 2

what is the effective mass equation

Answer 2

m* = ħ^2/[d^2E/dk^2]

Question 3

what is effective mass

Answer 3

measure of interactions with the lattice

Question 4

define a hole

Answer 4

empty state near the top of a valence band with positive effective mass and positive charge

Question 5

what is the Hall field equation

Answer 5

EH = RHjxBz
j is current density
RH is the hall coefficient

Question 6

what is the Hall coefficient equation and its special case for holes

Answer 6

RH = -1/ne
RH = 1/ρe
ρ is the hole concentration

Question 7

what can happen to electrons and holes at room temp

Answer 7

some electrons are excited from top of valence band to bottom of the conduction band
electrons at top of conduction band and holes at bottom of valence band are treated as charge carriers

Question 8

define an intrinsic semi conductor

Answer 8

conductor where conductivity is due to the intrinsic properties of the material itself so contains no impurities

Question 9

what is the condition for intrinsic semi conductors

Answer 9

n = p

number of conduction electrons = number of holes in valence band

Question 10

what is the probability of excitation for a charge carrier in an intrinsic semi conductor equation

Answer 10

P = n/N0 = exp[-EG/2kT]

Question 11

what is the ntype doping equation

Answer 11

ΔED = EC - ED = m*/m ER/ε^2

Question 12

what is the ptype doping equation

Answer 12

ΔEV = EA - EV