What is the current in the circuit shown below?

The energy of a photon in a monochromatic light of wavelength $621 \ nm$ matches with the band gap of a semiconducting material. Then the minimum energy required to create an electron-hole pair from the semiconductor is
[Take $hc = 1242 \ eV-nm$,where $h$ is Planck's constant and $c$ is speed of light in vacuum] (in $eV$)

The forward biased diode connection is:

Can we take one slab of $p-$type semiconductor and physically join it to another $n-$type semiconductor to get $p-n$ junction?

The magnitude of the diffusion current in a $p-n$ junction is smaller than the magnitude of the drift current:

To make a $PN$ junction conducting,