In the illustrated amplifiers in all three figures, in terms of doping, the base of the silicon semiconductor transistor is what type of material? See illustration EL-0022.
• Identify whether the illustrated transistor symbol is NPN or PNP by looking at the arrow on the emitter • Remember the basic physical structure of a bipolar junction transistor (BJT): emitter–base–collector layers • Think about majority carriers in N‑type vs P‑type material (free electrons vs holes)
• From the arrow direction on the emitter, what type of transistor is shown, and therefore what must the base region be? • In a standard silicon transistor, is the base region heavily or lightly doped compared with the emitter, and what does that do to the number of free electrons? • For the base material you identified, are holes or electrons the majority carriers, and how does that relate to the phrase decreased free electrons ?
• Confirm from the symbol that all three figures use the same transistor type (NPN or PNP) • Make sure the base region in that transistor type is the opposite conductivity type from the emitter and collector on either side • Match the correct option to a base that has holes as majority carriers and therefore fewer free electrons than N‑type material
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