Which semiconductor device converts electrical energy into light?

Consider the following statements $A$ and $B$ and identify the correct answer:
$A$. For a solar-cell,the $I-V$ characteristics lies in the $IV$ quadrant of the given graph.
$B$. In a reverse biased $pn$ junction diode,the current measured in $(\mu A)$ is due to majority charge carriers.

In optical fiber communication, an $APD$ semiconductor is used for:

What kind of diode is used as a photo detector?

Why is the $I-V$ characteristic of a solar cell drawn in the fourth quadrant of the coordinate system?

$A$ photodiode is a device