Draw V-I characteristics of a p-n junction diode. Explain why the current under reverse bias is almost independent of the applied voltage up to the critical voltage.
Explanation: The V-I characteristics of a p-n junction diode illustrate the relationship between current and voltage, showing how current varies with voltage. This relationship is non-linear, and the current is influenced by minority carriers in the junction.
Complete Answer:
The V-I characteristics of a p-n junction diode depict the connection between current and voltage, as illustrated below.
On the graph, the X-axis represents voltage (potential), while the Y-axis represents current through the diode.
When the p-n junction diode is reverse biased, the p-type semiconductor is connected to the negative terminal of the battery, and the n-type is connected to the positive terminal. In this configuration, holes in the p-type region are attracted to the negative terminal, while electrons in the n-type region are drawn to the positive terminal. This leads to an increase in the depletion layer width due to the barrier potential.
As a result, only a small current flows, primarily from minority charge carriers drifting across the junction. At normal temperatures, this reverse current remains very low, and any change in the applied voltage results in negligible changes in current. Thus, we can conclude that the current under reverse bias is nearly independent of the applied voltage.
Note: In reverse bias, the built-in electric field and the applied electric field are aligned in the same direction. When combined, they increase the effective electric field, resulting in higher resistance in the diode and a wider depletion layer.