Which transistor type is formed by placing a lightly doped N-type region between two P-type regions?

Which transistor type is formed by placing a lightly doped N-type region between two P-type regions?

• A. NPN Transistor
• B. PNP Transistor
• C. Photo Detector
• D. Insulated Gate FET

Answer: (B)

This arrangement describes a PNP transistor. In a PNP, the outer regions are P-type and the region in between is N-type serving as the base. The base is lightly doped and sandwiched between two P-type regions (emitter and collector), which is why the device operates with hole carriers mainly moving from the emitter to the collector when the emitter-base junction is forward biased. Understanding the structure helps: the base is the thin, lightly doped region that controls the flow of carriers between the two heavily doped outer regions. If you swapped the types so that the middle region were P-type and the outer regions N-type, you’d have an NPN transistor, not the described arrangement. A photo detector isn’t defined by this bipolar arrangement, and a MOSFET (insulated-gate FET) is a totally different device with a gate oxide insulator, not two junctions between alternating doped regions.

This arrangement describes a PNP transistor. In a PNP, the outer regions are P-type and the region in between is N-type serving as the base. The base is lightly doped and sandwiched between two P-type regions (emitter and collector), which is why the device operates with hole carriers mainly moving from the emitter to the collector when the emitter-base junction is forward biased.

Understanding the structure helps: the base is the thin, lightly doped region that controls the flow of carriers between the two heavily doped outer regions. If you swapped the types so that the middle region were P-type and the outer regions N-type, you’d have an NPN transistor, not the described arrangement. A photo detector isn’t defined by this bipolar arrangement, and a MOSFET (insulated-gate FET) is a totally different device with a gate oxide insulator, not two junctions between alternating doped regions.