Lecture on Introduction of Semiconductor at North South University as the undergraduate course (ETE411) ======================= Dr. Mashiur Rahman Assistant Professor Dept. of Electrical Engineering and Computer Science North South University, Dhaka, Bangladesh http://mashiur.biggani.org

1. ETE444 :: Lec15
Dr. Mashiur Rahman
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
ic

iE
ic

iB
α = Common-Base current gain
β = Common-Emitter gain

8. Four operation mode of bipolar transistor
n

9. 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

10. 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

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

12. 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

14. Application
• Voltage amplifier by Bipolar Transistors
• Switching

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

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

17. 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.