The $I-V$ characteristics for a junction diode are shown. The device is

$LED$ is constructed from $GaAsP$ semiconducting material. The energy gap of this $LED$ is $1.9\, eV$. Calculate the wavelength of light emitted and its colour.
$[h = 6.63 \times 10^{-34} \, Js$ and $c = 3 \times 10^{8} \, ms^{-1}]$

Why are $Si$ and $GaAs$ preferred materials for solar cells?

The semiconductor used for the fabrication of visible LEDs must at least have a band gap of (in $eV$)

Three photodiodes $D_1, D_2,$ and $D_3$ are made of semiconductors having band gaps of $2.5 \ eV, 2 \ eV,$ and $3 \ eV,$ respectively. Which ones will be able to detect light of wavelength $6000 \ \mathring{A}$?

The symbolic representation of a photodiode is: