Question-1: Calculate the minority electron concentration at the junction edge (or depletion edge) of the p-type at forward bias volatage of V=0.4, 0.55, and 0.7. Assume that the minority electron concentration at equilibrium is np0 = 1000 electrons/cm3 and use the formula np = np0 exp(V/VT) where VT = 0.025 V at room temperature.

Answer:

V=0.4: np = np0 exp(V/VT) = 1E3 * exp(0.4/0.025) = 1E3 * 8.886E6= 8.886E9 electrons/cm3.

V=0.55: np = np0 exp(V/VT) = 1E3 * exp(0.55/0.025) = 1E3 * 3.585E9 = 3.585E12 electrons/cm3.

V=0.7: np = np0 exp(V/VT) = 1E3 * exp(0.7/0.025) = 1E3 * 1.446E12 = 1.446E15 electrons/cm3.

Note: In an NPN bipolar transistor, the forward-biased emitter-base NP junction has a typical voltage drop of 0.7 Volts. The injected minority electron concentration at the junction edge in the Base will be about 1.5E15 electrons/cm3 if the base doping is NA=1E17 cm-3.