Forward Bias:

A diode is forward biased whenever the positive terminal of a voltage source is connected to its anode, and the negative terminal is linked to the cathode Figure. The power source's positive side will tend to repel the holes in the p-type material toward the p-n junction by the negative side. Hole is a vacancy in the electron structure of a material. It behaves as positive charges. The holes and the electrons reach the p-n junction, a few of them break by it Figure. Holes merge along with electrons in the n-type material and electrons merge within holes in the p-type material.

Figure: Forward-Biased Diode

When a hole merges along within an electron or an electron combines with a hole near the p-n junction, an electron from an electron-pair bond in the p-type material breaks its bond and enters the positive side of the source. Concurrently, an electron from the negative side of the source enters the n-type material Figure.  This generates a flow of electrons in the circuit.