What is a diode?

The electrical resistance of the depletion layer is large because

For a $p-n$ junction,the intensity of the electric field is $1 \times 10^{6} \text{ V/m}$ and the width of the depletion region is $5000 \text{ Å}$. The value of the potential barrier is $\dots \text{ V}$.

Which of the following statements concerning the depletion zone of an unbiased $PN$ junction is (are) true?
$(A)$ The width of the zone is independent of the densities of the dopants (impurities).
$(B)$ The width of the zone is dependent on the densities of the dopants.
$(C)$ The electric field in the zone is produced by the ionized dopant atoms.
$(D)$ The electric field in the zone is provided by the electrons in the conduction band and the holes in the valence band.

The band gap in a semiconductor is $0.6 eV$. The maximum wavelength of electromagnetic radiation which can create a hole-electron pair in this semiconductor is equal to [Use $hc = 1242 eV-nm$]. (in $nm$)

If the two ends $P$ and $N$ of a $P-N$ junction diode are joined by a wire,what happens?