Electronic Devices

In semiconductors, the charge carrier density $n$ increases exponentially with temperature:

Since resistivity is inversely proportional to carrier density:

As temperature $T$ increases, resistivity $\rho$ decreases rapidly (exponential decay).

Graph 3 correctly represents this non-linear exponential decrease of resistivity with temperature.

In forward bias, the positive terminal of the battery is connected to the p-side and the negative terminal to the n-side:

• The applied forward voltage opposes the built-in junction barrier potential: $V_{\text{eff}} = V_0 - V$.
• This opposition weakens the junction electric field and pushes majority carriers (holes from p-side and electrons from n-side) toward each other across the junction.
• Consequently, the width of the depletion layer reduces and junction resistance drops dramatically, enabling significant forward current.

Matching electronic devices with their primary applications:

• Photodiode: Operated in reverse bias to detect optical signals as a Photo detector (Matches IV).
• Zener diode: Operates in reverse breakdown region to provide constant output voltage as a Voltage regulator (Matches III).
• Light Emitting Diode (LED): Emits spontaneous radiation in forward bias, widely used in optical displays and infrared Remote controls (Matches I).
• Transistor: Used in active region to amplify small alternating signals as an Amplifier (Matches II).

Correct matching is (A)-(IV), (B)-(III), (C)-(I), (D)-(II). Hence, option 2 is the correct answer.