Explain V-I characteristics of a PN junction diode and show that PN diode works as a Rectifier.

V-I Characteristics of a PN Junction Diode:

A PN junction diode is a fundamental electronic component consisting of two semiconductor regions, namely the P-type region and the N-type region, joined together to form a rectifying junction. The electrical behavior of a PN junction diode can be described by its current-voltage (I-V) characteristics, which exhibit distinct regions depending on the applied voltage.

1. Forward Bias:

When a positive voltage is applied to the P-side and a negative voltage to the N-side of the diode, the diode is said to be forward biased. In this bias condition, the potential barrier at the junction is reduced, allowing majority carriers (electrons in N-type and holes in P-type) to cross the junction more easily. This leads to a significant increase in current flow.

The I-V characteristic in the forward bias region is nonlinear and exponential. The forward current (I_F) increases rapidly with increasing forward voltage (V_F) according to the Shockley equation:

   I_F = I_S (e^(V_F / (n * V_T)) - 1)

where:

• I_S is the reverse saturation current
• n is the ideality factor
• V_T is the thermal voltage (approximately 26 mV at room temperature)

1. Reverse Bias:

When a negative voltage is applied to the P-side and a positive voltage to the N-side of the diode, the diode is said to be reverse biased. In this bias condition, the potential barrier at the junction is increased, hindering the movement of majority carriers across the junction. As a result, the reverse current (I_R) remains very small and is typically in the nanoampere range.

The I-V characteristic in the reverse bias region is nearly flat, indicating that the reverse current is relatively independent of the reverse voltage (V_R) up to a certain voltage limit known as the breakdown voltage (V_BR). Beyond this voltage, the reverse current increases sharply due to mechanisms such as avalanche breakdown or Zener breakdown, potentially damaging the diode.

PN Diode as a Rectifier:

The rectifying property of a PN junction diode arises from its asymmetric I-V characteristics. When an alternating current (AC) signal is applied to the diode, it allows current to flow in one direction (forward bias) while blocking current in the opposite direction (reverse bias). This behavior enables the diode to convert AC into direct current (DC).

In a basic rectifier circuit, an AC input signal is connected to the diode in series with a load resistor. During the positive half-cycle of the AC signal, the diode is forward biased, allowing current to flow through the circuit and the load resistor. This results in a positive voltage across the load.

During the negative half-cycle, the diode is reverse biased, blocking current flow. Therefore, no current flows through the circuit, and the voltage across the load is zero. As a result, the output waveform is rectified, removing the negative half-cycles and producing a pulsating DC waveform.

The efficiency of the rectification process depends on the diode's forward voltage drop, switching speed, and power handling capability. PN junction diodes are widely used in rectifier circuits due to their low forward voltage drop, fast switching speed, and ability to handle high currents.