Three-element semiconductor formed by placing a lightly doped, very thin region of N-type silicon or germanium between two regions of P-type material

Three-element semiconductor formed by placing a lightly doped, very thin region of N-type silicon or germanium between two regions of P-type material

• A. PNP Transistor
• B. NPN Transistor
• C. Photo Detector
• D. P-Channel MOSFET

Answer: (A)

The structure described is a bipolar junction transistor, which contains three regions arranged as emitter, base, and collector. The outer regions are of one type (P-type) and sandwich a very thin, lightly doped region of the opposite type (N-type) in the middle. When the central region is N-type and unusually thin while the outer regions are P-type, that middle layer acts as the base, and the device is a PNP transistor. This arrangement is chosen because the thin, lightly doped base allows holes from the P-type emitter to be injected into the base and then swept into the collector with only a small base current, producing current gain. In a PNP transistor, the majority carriers are holes, and current flow is from emitter to collector under the proper biasing. A photodetector is typically based on a PN junction and doesn’t form the same emitter-base-collector arrangement with gain, and a P-channel MOSFET operates with a gate-controlled channel and isn’t formed by three doped regions in the same sandwich configuration.

The structure described is a bipolar junction transistor, which contains three regions arranged as emitter, base, and collector. The outer regions are of one type (P-type) and sandwich a very thin, lightly doped region of the opposite type (N-type) in the middle. When the central region is N-type and unusually thin while the outer regions are P-type, that middle layer acts as the base, and the device is a PNP transistor.

This arrangement is chosen because the thin, lightly doped base allows holes from the P-type emitter to be injected into the base and then swept into the collector with only a small base current, producing current gain. In a PNP transistor, the majority carriers are holes, and current flow is from emitter to collector under the proper biasing. A photodetector is typically based on a PN junction and doesn’t form the same emitter-base-collector arrangement with gain, and a P-channel MOSFET operates with a gate-controlled channel and isn’t formed by three doped regions in the same sandwich configuration.