The document discusses the four operation modes of a bipolar transistor: cutoff, forward active, inverse active, and saturation. It describes the characteristics of each mode, including the bias conditions and minority carrier distributions. Additionally, it covers two applications of bipolar transistors - as voltage amplifiers and for switching. It notes important switching parameters like current gain, base doping, switching time, and using gold doping to introduce recombination centers to reduce switching time.

1. ETE444 :: Lec15 Dr. MashiurRahman Copyright: Semiconductor Physics And Devices 3rd ed. - J. Neamen

2. Forward-active mode

4. Injection and collection of electrons

5. iE1= due to the flow of electrons injected into the base = ic α = Common-Base current gain β = Common-Emitter gain

7. Four operation mode of bipolar transistor n

8. Cuttoff mode VCB> 0 VBE < 0 B-E = reverse biased  Mejority carrier electrons from the emitter will not injected into the bias Minority carrier distribution

9. Forward active mode The B-E junction becomes forward biased, an emitter current will be generated and the injection of electrons into the base results in a collector current VCB> 0 VBE > 0 Minority carrier distribution

10. Inverse active The B-E forward biased and C-B VCB < 0 VBE < 0 Minority carrier distribution

11. Saturation mode Both B-E and B-C junctions are forward biased and the collector current no longer controlled by the B-E voltage. VCB< 0 VBE > 0 Minority carrier distribution

13. Application Voltage amplifier by Bipolar Transistors Switching

14. Voltage amplifier by Bipolar Transistors Input sinusoidal signal voltage Sinusoidal voltage across the Rc resistor Sinusoidal collector currents Sinusoidal base currents

15. Switching Storage time Raise time Fall time Circuit used for transistor switching Delay time

16. Switching :: Important parameter Current gain lower doping in the base region is used. Switching time The transistor can be doped with gold to introduce midgap recombination centers and thus reduce the switching time.