Problem set of report 4
1. For a uniformly doped n++p+n BJT in thermal equilibrium, a) sketch the energy band diagram, b)
sketch the electric field through the device, and c) repeat parts a) and b) for the BJT biased in the
forward active region.
2. A BJT is biased in the forward-active region. a) For a base current of IB = 4.2 uA and a collector
current of IC = 0.625 mA, determine , , and IE. b) For a collector current of IC = 1.254 mA and
emitter current of IE = 1.273 mA, determine , , and IB. c) For a base current of IB = 0.65 uA and
a common-emitter current gain  = 150, determine , IC, and IE.
3. Assume that an npn BJT has a common emitter current gain of  = 100. a) Sketch the ideal
current-voltage characteristics (IC versus VCE) as IB varies from zero to 0.1 mA in 0.01 mA
increments. Let VCE vary over the range 0<VCE<10V. b) Assuming VCC = 10V and RL = 1k in the
circuit below, superimpose the load line on the transistor characteristics in part a). c) Plot, on the
resulting graph, the value of IC and VCE corresponding to IB = 0.05 mA.
4. A uniformly doped Si npn BJT at T = 300K is biased in the forward-active mode. The doping
concentrations are NE = 8x1017 cm-3, NB = 2x1016 cm-3, and NC = 1015 cm-3. a) Determine the
thermal equilibrium values pEO, nBO, pCO. b) For VBE = 0.640 V, calculate the values of nB at x = 0
and pE at x” = 0”. c) Determine the B-E voltage such that the minority electron concentration, nB,
at x = 0 is 10 percent of the majority hole concentration. d) At this bias, determine the minority
hole concentration at x” = 0”. e) Sketch the minority carrier concentrations through the device and
label each curve.
5. An npn Si BJT at T = 300K has uniform dopings of NE = 1019 cm-3, NB = 1017 cm-3, and NC =
7x1015 cm-3. The BJT is operating in the inverted-active mode with VBE = -2V and VBC = 0.565 V. a)
Sketch the minority carrier distribution through the device. b) Determine the minority carrier
concentration at x = WB and x’ = 0’. c) If the metallurgical base width is W = 1.2 um, determine
the neutral base width WB.