What kind of $p-n$ junction diode does not require any kind of bias?

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.

An $LED$ is constructed from a $pn$ junction based on a certain semiconducting material whose energy gap is $1.9 \ eV$. The wavelength of the emitted light is:

Photodiodes are mostly operated in reverse biased condition because

The $I-V$ characteristic of an $LED$ is represented by which of the following graphs?

The photodiode is made of a material with a band gap of $2.0\, eV$. The minimum frequency of the radiation that can be absorbed by the material is nearly