Semiconductor Devices: Match Device Type to Its Defining Description List I A. BJT B. SCR C. UJT D. PUT List II 1. Current-controlled current source (three-layer, bipolar junction transistor) 2. Four-layer PNPN thyristor with latching behavior 3. Unijunction device exhibiting negative resistance, used for triggering/relaxation 4. Programmable unijunction transistor (thyristor-type) with adjustable triggering via gate

Introduction / Context:
Power electronics and analog circuits use a variety of semiconductor devices, each with distinct structures and operating principles. Correctly identifying device types and their defining characteristics is fundamental for selecting components and analyzing circuits.

Given Data / Assumptions:

• BJT: bipolar junction transistor.
• SCR: silicon controlled rectifier.
• UJT: unijunction transistor.
• PUT: programmable unijunction transistor.

Concept / Approach:

Map each device to its canonical description. BJTs behave as current-controlled current sources in amplifier regions. SCRs are four-layer PNPN devices with latching and controlled turn-on via gate. UJTs are two-layer, three-terminal devices with a negative resistance region used in oscillators and triggering. PUTs are thyristor-type devices functionally similar to UJTs but with programmable triggering via a gate-coupled reference junction.

Step-by-Step Solution:

Verification / Alternative check:

Datasheets and textbooks align with these archetypal definitions and application notes (e.g., UJT relaxation oscillators, SCR phase control, PUT waveform generators).

Why Other Options Are Wrong:

Swapping any two descriptions assigns incorrect physics (e.g., calling a UJT a PNPN device), which would mislead design choices.

Common Pitfalls:

Confusing UJT and PUT; while similar in use, PUT is a thyristor structure and offers programmable threshold via gate bias.

Final Answer:

A-1, B-2, C-3, D-4