Semiconductors and Semiconducting Devices — Practice Quiz

4.9 mA

Step 1: The fundamental current relationship in a transistor is: I_E = I_C + I_B. Step 2: Rearranging: I_C = I_E - I_B. Step 3: Substituting values: I_C = 5 mA - 0.1 mA. Step 4: I_C = 4.9 mA. Wrong options: 5.1 mA results from adding instead of subtracting. 5.0 mA ignores the base current. 0.5 mA is a random incorrect calculation.

Conduction band

Step 1: In the energy band model of solids, electrons occupy different energy bands. Step 2: The valence band contains electrons that are tightly bound and involved in covalent bonding. Step 3: When electrons gain sufficient energy (more than the band gap), they jump to the conduction band. Step 4: Electrons in the conduction band are free to move and contribute to electrical conduction. Wrong options: The valence band electrons are bound and do not freely conduct. The forbidden energy gap has no allowed energy states. 'Core band' is not a standard term in this context.

Current is negligibly small (almost zero)

Step 1: Knee voltage (also called threshold voltage) is the minimum forward bias voltage required to overcome the barrier potential and allow significant current to flow. Step 2: For Silicon, the knee voltage is about 0.7 V. Step 3: Below this voltage, the applied potential is not sufficient to overcome the depletion layer barrier. Step 4: Hence, the current is negligibly small or almost zero below the knee voltage. Wrong options: Large current flows only after the knee voltage is exceeded. Reverse current occurs in reverse bias, not forward bias. Breakdown occurs only in reverse bias at high

Base

Step 1: A transistor has three regions: Emitter, Base, and Collector. Step 2: The emitter is the most heavily doped region as it must inject a large number of charge carriers. Step 3: The collector is the largest region as it must collect most of the charge carriers and dissipate heat. Step 4: The base is the thinnest and most lightly doped region. This is crucial so that most of the charge carriers injected by the emitter pass through the base and reach the collector without recombining. Wrong options: Emitter is most heavily doped. Collector is largest in size. Depletion region is not one of