In a bipolar junction transistor (BJT), what is the approximate barrier potential across the emitter–base junction for silicon devices at room temperature?

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Solve this multiple-choice question and choose the correct option.

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Introduction / Context:The barrier potential (also called built-in potential) is critical for understanding forward biasing of BJTs and diodes. Knowing its approximate value for silicon and germanium helps predict conduction onset voltages and biasing requirements. Given Data / Assumptions: Material: silicon. Temperature: approximately 300 K. Junction type: emitter–base junction of a BJT. Concept / Approach:For silicon junctions at room temperature, the built-in potential is about 0.7 V. This is the voltage required to overcome the depletion region barrier and allow significant current flow under forward bias. Germanium devices, by contrast, exhibit ~0.3 V. Step-by-Step Solution: Identify junction: emitter–base p–n junction.Recall built-in potential for Si ≈ 0.7 V, Ge ≈ 0.3 V.Therefore, total barrier potential = 0.7 V. Verification / Alternative check: Practical measurement: Si diode forward conduction starts around 0.6–0.7 V, matching theoretical barrier. Why Other Options Are Wrong: 0: unrealistic, ignores depletion region.0.7 V across each layer: misleading; the total across depletion is ~0.7 V, not per layer.0.35 V: corresponds to Ge approximations, not Si.1 V: too high for typical Si devices. Common Pitfalls: Confusing Ge with Si; misunderstanding that 0.7 V is approximate, not exact. Final Answer: a total of 0.7 V

In a bipolar junction transistor (BJT), what is the approximate barrier potential across the emitter–base junction for silicon devices at room temperature?

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