The photocurrent in a photodiode depends on

What kind of diode is used as a photo detector?

$(i)$ Name the type of diode whose characteristics are shown in figure $(a)$ and figure $(b)$.
$(ii)$ What does the point $P$ in figure $(a)$ represent?
$(iii)$ What do the points $P$ and $Q$ in figure $(b)$ represent?

Which of the following statements is not correct in the case of light emitting diodes?

The material used for a solar cell should have a band gap:

Assertion $(A)$: $Si$ and $GaAs$ are the preferred materials for solar cells.
Reason $(R)$: Both these materials have energy band gaps much below the energy level corresponding to the maximum solar irradiance in the solar spectrum.