hole density i.s calculated by assuming that the:density of carriers is determined by the impurities present in the silicon sample. The density of ionized acceptor impurities in p-type silicon is computed from the charge neutrality equation
- +
NA N0 = p -n (4.3)
This reduces to
p NA (4.4)
for the case of uncompensated material.
The density of ionized acceptors is [56]
NA
NA = (4.5)
1 + g exp[ kTFJ
where EA is the acceptor ionization energy, and g is the ground state degeneracy. Excited states have a very minor influence on the carrier concentration due to the large separation between the ground state and the 'excited states [1,56]. Letting
g = 4 + 2 exp[- k-J (4.6)
enables us to include the contribution of the split-off band [17]. The density of ionized acceptors is computed by iterating EF in equations (4.2) and (4.5) until equation (4.4) is fulfilled within a given level of accuracy.