BJT Device Physics Explorer — ICD, University of Twente

Bias

V_BE

V_CE

Device

Emitter doping N_DE

Base doping N_AB

Collector doping N_DC

Base width W_B0 (junction to junction)

Emitter depth W_E

Base lifetime τ_B

Emitter lifetime τ_E

Depletion-layer lifetime τ_SCR

Emitter area A_E

Temperature T

Physics switches

SRH recombination in the B–E depletion layer (non-ideal exp(V_BE/2V_T) base current → low-current β roll-off) Recombination in the neutral base (finite τ_B, base transport factor α_T < 1) Base-width modulation by the depletion layers (Early effect) High injection in the base (Webster effect: once n > N_AB the slope halves and I_C levels off — switch off to see the ideal exponential) Terminal series resistances R_E, R_B (the junction sees less than the pin, so the Gummel plot bends into an ohmic line at the top) Kirk effect / base push-out at high J_C

Collector epi thickness W_epi

Avalanche multiplication in the B–C junction

R_E

R_B

Emitter band-gap narrowing ΔE_g

Presets

Operating point

Where every electron and hole goes

electron flux hole flux recombination event collected current

Decomposition of the base current

Minority-carrier profiles

logarithmic concentration axis show profile at V_CE = 0.3 V (compare base widths)

Δn in base Δp in emitter same device at low V_CE tangent → J_C

Energy bands and quasi-Fermi levels

E_C, E_V E_Fn E_Fp depletion layer

Transfer characteristics I_C(V_BE) and I_B(V_BE)

compare three V_CE values wide V_BE range (whole turn-on) logarithmic current axes

I_C I_B other V_CE values

Current gain β_FE = I_C/I_B versus V_BE

Gummel plot — log I_C and log I_B vs V_BE

Current gain β vs collector current

β total β limit from depletion-layer recombination β limit from base recombination β limit from emitter back-injection

Output characteristics I_C(V_CE)

step I_B (constant base current) step V_BE show Early extrapolation

Neutral base width vs V_CE

Breakdown voltages of this device

actual limit mechanism not limiting here

Switch to Level 2 (top right) to add the f_T·BV trade-off plot, the mechanism-by-mechanism breakdown limits and the delay budget behind f_T.

The f_T · BV trade-off (Johnson limit)

sweep collector doping N_DC sweep epi thickness W_epi sweep base width W_B0 thin base (60 nm, 10¹⁸) + epi sweep Johnson limit f_T·BV = v_satE_c/2π