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In an unbiased pnp transistor, the barrier voltages are ___________ on the base and ___________ on the emitter and collector.
negative; negative
positive; positive
negative; positive
positive; negative
positive; negative
In an unbiased pnp transistor, the electrostatic potential is higher in the p-type regions (emitter and collector) compared to the n-type base region. The potential difference creates a barrier, resulting in a positive potential relative to the base at the emitter and collector junctions, or conversely, the base acts as a positive barrier relative to the emitter and collector regions.
In an unbiased pnp transistor, the electrostatic potential is higher in the p-type regions (emitter and collector) compared to the n-type base region. The potential difference creates a barrier, resulting in a positive potential relative to the base at the emitter and collector junctions, or conversely, the base acts as a positive barrier relative to the emitter and collector regions.
╧ХbтАЛ=qkTтАЛln(ni2тАЛNAтАЛNDтАЛтАЛ) тАФ The built-in potential barrier voltage across the junction.
In thermal equilibrium, the Fermi levels of the p-type and n-type materials align, causing band bending at the junction. For a pnp transistor, the p-regions have a lower potential compared to the base region's n-type potential, or more precisely, the base possesses a positive built-in potential barrier ╧ХbтАЛ to prevent majority carrier diffusion. Conventionally, this manifests as a positive barrier voltage on the base relative to the emitter and collector regions.
A pnp transistor consists of two p-n junctions back-to-back.
The n-type base acts as a potential barrier for holes moving from the emitter to the collector.
The barrier voltage is defined by the difference in Fermi levels and doping concentrations.
In equilibrium, no net current flows due to the balance of drift and diffusion currents.
Provides inherent isolation between regions in equilibrium.
Allows controlled switching when external bias is applied.
Requires external biasing to overcome the barrier for active operation.
Barrier height is temperature dependent.
BJT amplifier circuits.
Digital logic switching elements.
The barrier voltage is synonymous with the built-in potential ╧ХbiтАЛ.
Option A is incorrect as potential cannot be negative for both sides in the standard equilibrium model.
Option C suggests negative for base, which contradicts the physics of p-n junction potential alignment.
D is correct тАФ In an unbiased pnp transistor, the base region is at a higher potential relative to the emitter and collector, creating a positive potential barrier at the base and a negative potential barrier at the emitter/collector regions.
Remember that the built-in potential always opposes the majority carrier flow, and the base region in a pnp transistor is n-type, which inherently sits at a higher potential than the p-type regions in equilibrium.
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