The energy band gap of a semiconducting material required to produce a violet (wavelength $= 4000 \, \mathring{A}$) $LED$ is $....... \, \text{eV}$. (Round off to the nearest integer).

What kind of diode is used as a photo detector?

The bandgap of the material of a photodiode is $2.0 \ eV$. What is the minimum frequency of radiation that this material can absorb?

In an $LED$,when forward bias is increased (starting from zero),the intensity of emitted light will:

$A$ $p-n$ junction is fabricated from a semiconductor with a band gap of $2.8 \ eV$. What approximate wavelength can it $NOT$ detect (in $nm$)?
[Use $h = 6 \times 10^{-34} \ J \cdot s$ and $c = 3 \times 10^8 \ m/s$]

Explain the construction and working of a photodiode.