Semiconductor

The diode is reverse biased.

Step 1: In the given circuit, the negative terminal ( ) is connected to the -side, and the positive terminal ( ) is connected to the -side.

Step 2: Since the -side is at a lower potential, the junction is reverse biased.

Step 1: Forward Biasing In forward biasing, the external voltage applied reduces the potential barrier of the depletion region, allowing current to flow easily through the junction.

• The positive terminal of the battery is connected to the -side, and the negative terminal to the -side.
• As the barrier potential decreases, more charge carriers (electrons and holes) cross the junction.
• The current increases exponentially with applied voltage.

Example: Forward biasing is used in rectifiers and LEDs. Current in forward bias }  

Step 2: Reverse Biasing In reverse biasing, the external voltage increases the potential barrier, preventing the flow of majority carriers and widening the depletion region.

• The positive terminal is connected to the -side, and the negative terminal to the -side.
• Only a small leakage current flows due to minority carriers.
• Beyond a certain voltage, breakdown occurs, causing a large current to flow.

Example: Reverse biasing is used in Zener diodes and photodiodes.  

Step 3: Difference Between Forward and Reverse Current

Step 1: An n-type semiconductor is created by doping a pure semiconductor with elements having more electrons.

Step 2: Despite having free electrons, the overall charge of the semiconductor remains neutral because the number of positive protons in the nuclei balances the charge.

Step 1: Circuit Diagram for Forward Bias of p-n Junction Diode.
To obtain the characteristic curve of a p-n junction diode in forward bias, we need to connect the diode in a circuit with a variable power supply. The positive terminal of the power supply is connected to the p-type side (anode) of the diode, and the negative terminal is connected to the n-type side (cathode).
Step 2: Explanation of Circuit Diagram.
- A power supply provides a varying voltage across the diode.
- The anode of the diode is connected to the positive terminal, and the cathode to the negative terminal of the power supply.
- A milliammeter is connected in series with the diode to measure the current that flows through the circuit.
Step 3: Characteristic Curve.
When the diode is forward biased, the current increases as the applied voltage increases beyond a threshold (typically around 0.7V for silicon diodes). At lower voltages, the current is almost zero, but as the voltage increases, the current increases exponentially. The characteristic curve of a p-n junction diode in forward bias shows this exponential increase.
Step 4: Effect of Forward Bias on the Depletion Region.
- In forward bias, the external voltage decreases the width of the depletion region, allowing more charge carriers to recombine at the junction.
- As the forward voltage increases, the potential barrier decreases, and more charge carriers can cross the junction, leading to an increase in current.
Final Answer: In forward bias, the depletion region becomes narrower, and the current increases exponentially with the applied voltage after a certain threshold.