APPENDIX A. LIST OF SYMBOLS 515
VSB source to body (substrate) potential
Vr(Vf) reverse (forward) bias voltage in a diode
VBE,VBC base to emitter, base to collector bias in a bipolar transistor
Vpt punchthrough voltage
Wn(Wp) depletion region edge on then-side (p-side) of ap-njunction
W depletion region width
Wb,Wbn base width, neutral base width of a bipolar transistor
α optical absorption coefficient
α current transfer ratio in a bipolar transistor
αR reflection loss coefficient in an optical cavity
αimp impact ionization coefficient for electrons
β base to collector current amplification factor in a BJT
βimp impact ionization coefficient for holes
γe emitter efficienty of a bipolar transistor
γinj injection efficiency of ap-ndiode for electron (hole) current
ΔEg bandgap difference between two materials
ΔEc,ΔEv band discontinuity in the conduction, valence band in a
heterostructure
o free space permittivity
product of the relative dielectric constant ando
ψ electron wavefunction
σn(σp) electron (hole) capture cross-section for an impurity
σ conductivity of a material
μ mobility of a material
μn(μp) electron (hole) mobility
τsc scattering time between successive collisions. Also called relaxation
time
ω frequency
τo rate at which an electron recombines radiatively with a hole at the
same momentum value
τr radiative recombination time fore-hpair
τnr non-radiative recombination time for ae-hpair
τn lifetime of an electron to recombine with a hole
τp lifetime of a hole to recombine with an electron
τsd storagedelaytimeinadiode
δn excess electron density in a region. This is the density above the
equilibrium density
δp excess hole density in a region
φm metal work function