An $LED$ is constructed from a $p-n$ junction diode using $GaAsP$. The energy gap is $1.9\; eV$. The wavelength of the light emitted will be equal to

Consider the following statements $:$
$A.$ The junction area of a solar cell is made very large compared to a photodiode.
$B.$ Solar cells are not connected with any external bias.
$C.$ $\text{LED}$ is made of heavily doped $p-n$ junction.
$D.$ Increase of forward current results in continuous increase of $\text{LED}$ light intensity up to a saturation point.
$E.$ $\text{LED}$ must be connected in forward bias for the emission of light.
Which of the following statements are correct?

Explain why elemental semiconductors cannot be used to make visible $LEDs$.

$A$ solar cell is to be fabricated for efficient conversion of solar radiation to emf using material $A$. The solar cell is to be mechanically protected with the help of a coating using material $B$. If the band gap energy of materials $A$ and $B$ are $E_{A}$ and $E_{B}$ respectively,then which of the following choices is optimum for better performance of the solar cell?

An $LED$ is a $p-n$ junction diode which is

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