In the fabrication of a PNP transistor, what is the primary reason for using a buried layer of heavily doped P+ material beneath the N-type base region?

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In the fabrication of a PNP transistor, what is the primary reason for using a buried layer of heavily doped P+ material beneath the N-type base region?

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RRB JE EE 22 Apr 2025 Shift 2 CBT 2 Official Paper

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To increase the emitter injection efficiency
To reduce the base-emitter voltage
To reduce the collector-emitter saturation voltage
To prevent latchup and improve transistor stability

Answer 1

PNP Transistor

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This bipolar PNP junction transistor is formed with three layers of semiconductor material, with two P-type regions and one N-type region. It includes three terminals: Emitter; Collector; and Base.

In the fabrication of a PNP transistor, a buried layer of heavily doped P+ material beneath the N-type base is introduced primarily to:

Prevent latchup, which is an unwanted triggering of a parasitic thyristor structure (common in CMOS technology).
Improve transistor performance and isolation by reducing substrate resistance and minimizing unwanted parasitic interactions.
Enhance collector conductivity, which also helps in maintaining stability under high-frequency and high-current conditions.

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In the fabrication of a PNP transistor, what is the primary reason for using a buried layer of heavily doped P+ material beneath the N-type base region?

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