Ch. 16 Electric Properties Flashcards
Ohms Law
I = V / R
Resistivity formula
P = R * A / L
Conductivity formula
σ = 1 / P
Valence band
Outermost filled band
Conduction band
Next available enrgy level
Imperfections increase…
Resistivity
Imperfection examples
Grain boundaries, Pores, Impurities, Dislocations, Vacancies
Metal resistivity increases w/:
T, %impurities, %cold work(causes dislocations)
Matthiesens rule
Ptotal = Pthermal + Pimpurity + Pdef
Pthermal =
P0 + aT (all constants exept T)
T in metals is directly proportional to: (why does T increase resistivity)
Vibrations = Electron scattering
%CW is directly proportional to
dislocations = P0
Pimpurity =
A * Ci * ( 1 - Ci) — Ci = impurity concentration)
Pimpurity for phased =
PaVa + PbVb
Charge carriers in insulators & instrinsic semiconductors
Free electrons and holes in valence bands
σ formula for insulators
σ = n *|e| * μe (electron mobility) + p * |e| * μh
for intrinsic semiconductors T is proportional to
σ (opposite to metals)
σ of undoped intrsinic semiconductors formula
σ proportional to exp ( - Egap / ( k * T ) )
Types of semiconductors
Intrinsic & Extrinsic
Relationbetween n and p in intrinsic semiconductors
n = #p
Extrinsic semiconductors
n != #p
N type
(n > p)
P type
(n < p)
Extrinsic semiconductors vs T
weird graph , extrinsic looks like “S”, intrinsic is exponential
P - N Rectifying Junction
P type and N type semiconductors together