The diode is forward biased. The positive terminal of the battery is connected to the anode of a diode and negative terminal to the cathode.
When battery is not connected, there is a barrier potential of 0.3 V for Silicon and 0.7 V for Germanium across the across the P-N junction of a diode.
Due to majority charge carriers the external applied voltage of forward bias is opposed by the barrier voltage and the diode does not conduct the current.
The applied voltage is increased above the barrier potential, it overcome the opposition of barrier potential and diode conducts the current due to majority carriers.
This current is known as forward current and flows from anode to cathode through the diode.
The negative terminal of the battery is connected to the anode of a diode and positive terminal of battery is connected to cathode. Hence, the diode is reverse bias.
When diode is reverse biased, majority carriers are blocked and only a small current flows through the diode due to the minority charge carriers.
As the reverse voltage is increased from zero, the reverse current very quickly reaches its saturation value which is also called as leakage current or reverses saturation current.
It is of the order of nanoamperes (nA) for Silicon and microamperes (µA) for Germanium.
