What is biasing?
When we connect diode with dc power supply or dc external source, it conducts as well as stops the flow of current. This process is called biasing. There are two types of biasing
- Forward Biasing
- Reverse Biasing
There are two conditions of forward biasing
- Connect positive terminal of battery with p-type area and negative terminal with n-type area
- The voltage provided must be greater than barrier potential
Fig-1: A forward bias diode
What does happen to diode in forward bias?
The negative terminal of the battery provides a consistent flow of electron. These electrons enter in the n-type area of diode. They push the free electrons of n-type area and provide them enough energy so they can break the barrier potential to move to the p-type area.
The positive side of the battery attract these electrons and provide a path way in terms of holes. These free electrons move from one hole to another.
The current produced by free electrons is called electronic current
As electrons move from one hole to another hole of the valence shell. It seems that holes are moving to opposite side of electron current. This is called hole current.
Unlike the forward bias ,there is only one condition for reverse bias operation of transistor
- Connect negative terminal of battery with p-type area and positive terminal of battery with n-type area
Fig-2: A reverse bias diode
What does happen to diode in reverse bias?
The positive side of the battery attract the free electrons of the n-type area. As a result they create more holes. On the other side the more electrons enter to p-type area from negative terminal of the battery. These electrons starts gathering near depletion region. So depletion region expands. (See Fig-3)
Fig-3: Effect of reverse bias on depletion region
Due to this process the majority carriers on both sides becomes depleted. A point reaches when barrier potential becomes equal to applied voltage. This condition stops the flow to current. A very small amount of current flow before this condition which is called leakage current.