When a BJT is operating in the normal active mode, the C-B junction is reverse-biased. The collector voltage, which determines the depletion layer width of the C-B junction, can thereby affect the actual base width.
a) Plot the minority carrier charge (i.e., holes) in the base region of a p-n-p transistor for two values of VCB, assuming that IE is kept constant. How is the base transport factor affected by this base width modulation (i.e., by the change of VCB)?
(b) Derive an expression of the output resistance for the transistor given in (a).
(c) For a planar silicon p+-n-p transistor with Lpb = 12 Âµm, Wb = 1 Âµm, VCB = 10 V, IC = 1 mA, ND = 1016 cmâˆ’3, and NA = 5 Ã— 1015 cmâˆ’3, calculate the output resistance for this transistor using the result derived in (b).