Explanation: A heavily doped n+ region is sandwiched between the n-type epitaxial collector and p-type substrate. This buried n+ region provide a low resistivity current path from active collector region (n-type layer) to the collector contact (n+ contact layer). In effect, the n+ layer shunt n-layer of collector region with respect to flow of current, thus effectively reduces the collector resistance. 7. At what potential, the substrate of a vertical pnp transistor should be kept to attain good isolation?
A. Same potential
B. Positive potential
C. Different potential
D. Negative potential
Answer:A
Explanation: A heavily doped n+ region is sandwiched between the n-type epitaxial collector and p-type substrate. This buried n+ region provide a low resistivity current path from active collector region (n-type layer) to the collector contact (n+ contact layer). In effect, the n+ layer shunt n-layer of collector region with respect to flow of current, thus effectively reduces the collector resistance. 7. At what potential, the substrate of a vertical pnp transistor should be kept to attain good isolation?
A. Same potential B. Positive potential C. Different potential D. Negative potential
Explanation: The limitation of vertical pnp transistor is that, collector has to be held at a fixed negative potential, as substrate is to be held at the most negative potential in the circuit for providing good isolation. 8. Which method is used in the fabrication of pnp transistor?