In a p-n junction, the width of the depletion layer changes depending on whether it is forward biased or reverse biased:

(i) Forward Biased:

• When a p-n junction is forward biased, the width of the depletion layer decreases.
• In forward bias, the positive terminal of the voltage source is connected to the p-type region, and the negative terminal is connected to the n-type region. This causes the majority carriers (holes in the p-type region and electrons in the n-type region) to move towards the junction.
• As the majority carriers move towards the junction, they neutralize some of the immobile ions in the depletion region, reducing the width of the depletion layer.
• The reduced width of the depletion layer allows for easier flow of current through the junction.

(ii) Reverse Biased:

• When a p-n junction is reverse biased, the width of the depletion layer increases.
• In reverse bias, the positive terminal of the voltage source is connected to the n-type region, and the negative terminal is connected to the p-type region. This creates an electric field that repels majority carriers away from the junction.
• As majority carriers are pushed away from the junction, the immobile ions in the depletion region create a larger electric field, widening the depletion layer.
• The widened depletion layer restricts the flow of current through the junction, resulting in very little current flow under reverse bias conditions.

In summary, forward biasing reduces the width of the depletion layer, facilitating current flow, while reverse biasing increases the width of the depletion layer, limiting current flow.

Explanation:

During the positive half-cycle of the AC input signal, the p-terminal of the diode becomes positive and the n-terminal becomes negative. This forward-biases the diode, allowing current to flow through it and the load resistor, completing the circuit. As a result, current flows through the load resistor and we get an output voltage across the load resistor.

During the negative half-cycle of the AC input signal, the p-terminal of the diode becomes negative and the n-terminal becomes positive. This reverse-biases the diode, blocking current flow through it, and thus no current flows through the load resistor. As a result, there is no output voltage across the load resistor during the negative half-cycle.

So, at the output, we get a pulsating DC signal which is the positive half-cycles of the AC input signal. This is why it's called a half-wave rectifier, as it rectifies only one half of the input AC waveform.

A photodiode is a semiconductor device that converts light into an electrical current. It is commonly operated under reverse bias for several reasons:

1. Increased Depletion Region: When a photodiode is reverse biased, the width of the depletion region increases. This widening of the depletion region allows for more efficient absorption of photons, enhancing the device's sensitivity to light.

2. Reduced Dark Current: Reverse biasing reduces the dark current of the photodiode. Dark current refers to the current that flows through the photodiode even when there is no light present. By operating under reverse bias, dark current is minimized, leading to better signal-to-noise ratio and improved performance in low-light conditions.

3. Faster Response Time: Reverse biasing can improve the response time of the photodiode. It reduces the capacitance of the photodiode, which in turn decreases the time it takes for the photodiode to respond to changes in incident light intensity.

4. Lower Noise: Reverse biasing helps in reducing the noise generated by the photodiode. This noise reduction contributes to better overall performance, especially in applications where precise measurements are required.

5. Linear Response: Reverse biasing allows for a more linear response of the photodiode to changes in incident light intensity over a wider range, making it suitable for applications requiring accurate light detection and measurement.

Overall, operating a photodiode under reverse bias enhances its performance in terms of sensitivity, response time, noise reduction, and linearity, making it suitable for various light detection applications such as in optical communication, light sensing, and imaging.