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A pn junction diode has a concentration of ${10}^{16}$ acceptor atoms $c{m}^{-3}$ on the p $-$side and a concentration of ${10}^{17}$ donor atoms $c{m}^{-3}$ on the n $-$side. What will be the built$-$in potential for the semiconductor materials $Ge,Si,$InP and GaAs $?$

Consider a $p^{+}n$ junction, which has a heavily doped p $-$side relative to the n $-$side, that is $N_a>>N_d.$ Since the amount of charge Q on both sides of the metallurgical junction must be the same. What is the depletion width for a pn junction Si diode that has been doped with ${10}^{18}$ acceptor atoms $c{m}^{-3}$ on the p $-$side and ${10}^{16}$ atoms $c{m}^{-3}$ on the n $-$side?

For the bipolar junction transistor $($BJT$),$ please explain the working mechanism when it functions as an amplifier.

How to find the operation point of a solar cell with maximum power output?