Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/ Semiconductor Device Modeling and Characterization EE5342, Lecture 12 -Sp 2002 Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/ L12 21Feb02

Bipolar junction transistor (BJT) E B C VEB VCB Charge neutral Region Depletion Region The BJT is a “Si sandwich” Pnp (P=p+,p=p-) or Npn (N=n+, n=n-) BJT action: npn Forward Active when VBE > 0 and VBC < 0 L12 21Feb02

BJT coordinate systems z x”c x” WB WB+WC -WE xB x x’E x’ Charge neutral Region Depletion Region Base Collector Emitter L12 21Feb02

BJT boundary and injection cond (npn) L12 21Feb02

BJT boundary and injection cond (npn) L12 21Feb02

IC npn BJT (*Fig 9.2a) L12 21Feb02

npn BJT bands in FA region q(VbiE-VBE ) q(VbiC-VBC ) qVBE qVBC injection high field L12 21Feb02

Coordinate system - prototype npn BJT (Fig 9.8*) L12 21Feb02

Notation for npn & pnp BJTs NE, NB, NC E, B, and C doping (maj) xE, xB, xC E, B, and C CNR widths DE, DB, DC Dminority for E, B, and C LE, LB, LC Lminority for E, B, and C (L2min = Dmin tmin) tE0, tB0, tC0 minority carrier life- times for E, B, and C regions L12 21Feb02

Notation for npn BJTs only pEO, nBO, pCO: E, B, and C thermal equilibrium minority carrier conc pE(x’), nB(x), pC(x’’): positional mathe- matical function for the E, B, and C total minority carrier concentrations dpE(x’), dnB(x), dpC(x’’): positional ma- thematical function for the excess minority carriers in the E, B, and C L12 21Feb02

Notation for pnp BJTs only nEO, pBO, nCO: E, B, and C thermal equilibrium minority carrier conc nE(x’), pB(x), nC (x’’): positional mathe- matical function for the E, B, and C total minority carrier concentrations dnE(x’), dpB(x), dnC(x’’): positional ma- thematical function for the excess minority carriers in the E, B, and C L12 21Feb02

npn BJT boundary conditions L12 21Feb02

Emitter solution in npn BJT L12 21Feb02

Base solution in npn BJT L12 21Feb02

Collector solution in npn BJT L12 21Feb02

Hyperbolic sine function L12 21Feb02

npn BJT regions of operation VBC Reverse Active Saturation VBE Forward Active Cutoff L12 21Feb02

npn FA BJT minority carrier distribution (Fig 9.4*) L12 21Feb02

npn RA BJT minority carrier distribution (Fig 9.11a*) L12 21Feb02

npn cutoff BJT min carrier distribution (Fig 9.10a*) L12 21Feb02

npn sat BJT minority carrier distribution (Fig 9.10b*) L12 21Feb02

Defining currents in FA mode npn BJT (Fig 9.13*) L12 21Feb02

npn BJT currents (F A region, ©RLC) IC = JCAC IB=-(IE+IC ) JnE JnC IE = -JEAE JRB=JnE-JnC JpE JGC JRE JpC L12 21Feb02

npn BJT topology x x’ p-Base n-Collector N-Emitter z WB WB+WC -WE x”c Charge Neutral Region Depletion Region x x’ p-Base n-Collector N-Emitter z WB WB+WC -WE x”c x” xB x’E IE IC IB L12 21Feb02

E current equations in FA mode npn BJT L12 21Feb02

C current equations in FA mode npn BJT L12 21Feb02

FA npn figure of merit emitter eff L12 21Feb02

FA npn figure of merit base transp L12 21Feb02

FA npn figure of merit recomb fact L12 21Feb02

E current equations in FA mode npn BJT L12 21Feb02

C current equations in FA mode npn BJT L12 21Feb02

References * Semiconductor Physics & Devices, by Donald A. Neamen, Irwin, Chicago, 1997. L12 21Feb02