ETE411 :: Lec14<br />Dr. MashiurRahman<br />
Contact<br />Rectifying contacts<br />Nonrectifying contacts (Ohmic contact)<br />
Nonrectifying contacts (Ohmic contact)<br />Before contact<br />After contact<br />Metal-n-semiconductor junction for Фm &...
Ohmic contact<br />Schotkey  Barrier<br />
Tunneling barrier<br />Energy-band diagram of a heavily doped n-semiconductor-to-metal junction<br />The space charge widt...
Voltage applied<br />Positive voltage applied to the metal<br />Positive voltage applied to the semiconductor<br />
Ohmic contact :: metal –p -semiconductor<br />(not included in the course)<br />
Example 9.7 (page 347)<br />
Transport mechanisms<br />Forward bias<br />S. M. Sze : Physics of semiconductor Devices  (page 254)<br />Transport mechan...
Transport of electrons from the semiconductor over the potential barrier into the metal.  Dominent process for Schottky d...
tunneling (‘through’ the barrier)<br />Quantum-mechanical tunneling of electrons through the barrier (important for heavil...
recombination in the depletion layer<br />Recombination in the space-charge region <br /> identical to the recombination ...
hole injection from metal<br />Hole injection from the metal to the semiconductor <br /> Recombination in the neutral reg...
Various metal-semiconductor device structure<br />
S. M. Sze : Physics of semiconductor Devices  (page 297)<br />
Chapter 10The Bipolar Transistor<br />
History<br />Bardeen, Brattain & Shockley<br />1948 : Invented the transistor<br />1956 : Received Nobel<br />Post war eff...
Block diagrams and circuit symbols<br />Bipolar: its operation involves both type of mobile carriers – electrons & holes.<...
Doping profile<br />n<br />n++<br />
Conventional ICs<br />An oxide-isolated npn bipolar transistor<br />Conventional npn transistor<br />From Muller and Kamin...
Forward active operating mode<br />n++<br />n<br />Electron injected: E -> B<br />Create excess concentration of minority ...
Minority carrier distribution <br />
Energy band diagram<br />
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Ete411 Lec14

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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

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Ete411 Lec14

  1. 1. ETE411 :: Lec14<br />Dr. MashiurRahman<br />
  2. 2. Contact<br />Rectifying contacts<br />Nonrectifying contacts (Ohmic contact)<br />
  3. 3. Nonrectifying contacts (Ohmic contact)<br />Before contact<br />After contact<br />Metal-n-semiconductor junction for Фm &lt; Фs<br />
  4. 4. Ohmic contact<br />Schotkey Barrier<br />
  5. 5. Tunneling barrier<br />Energy-band diagram of a heavily doped n-semiconductor-to-metal junction<br />The space charge width in a rectifying metal semiconductor contact is universally proportional to the square root of the semiconductor doping. <br />The width of the depletion region decrease as the doping concentration in the semiconductor increases.<br />
  6. 6. Voltage applied<br />Positive voltage applied to the metal<br />Positive voltage applied to the semiconductor<br />
  7. 7. Ohmic contact :: metal –p -semiconductor<br />(not included in the course)<br />
  8. 8. Example 9.7 (page 347)<br />
  9. 9. Transport mechanisms<br />Forward bias<br />S. M. Sze : Physics of semiconductor Devices (page 254)<br />Transport mechanisms at metal–semiconductor junctions. (1) Thermionic emission (‘above’ the barrier) (2) tunneling (‘through’ the barrier), (3) recombination in the depletion layer, (4) hole injection from metal<br />
  10. 10. Transport of electrons from the semiconductor over the potential barrier into the metal.  Dominent process for Schottky diodes with moderately doped semicondutor (Si with ND ≤1017cm-3) operated at moderate temperature (room temp.). <br />Thermionic emission<br />
  11. 11. tunneling (‘through’ the barrier)<br />Quantum-mechanical tunneling of electrons through the barrier (important for heavily doped semiconductors and responsible for most ohmic contacts).<br />
  12. 12. recombination in the depletion layer<br />Recombination in the space-charge region <br /> identical to the recombination process in a p-n junction. <br />
  13. 13. hole injection from metal<br />Hole injection from the metal to the semiconductor <br /> Recombination in the neutral region. <br />
  14. 14. Various metal-semiconductor device structure<br />
  15. 15.
  16. 16. S. M. Sze : Physics of semiconductor Devices (page 297)<br />
  17. 17. Chapter 10The Bipolar Transistor<br />
  18. 18. History<br />Bardeen, Brattain & Shockley<br />1948 : Invented the transistor<br />1956 : Received Nobel<br />Post war effort to replace vacuum tube.<br />They used Germanium: it was possible to obtain high purity material.<br />
  19. 19. Block diagrams and circuit symbols<br />Bipolar: its operation involves both type of mobile carriers – electrons & holes.<br />pnp<br />npn<br />n++<br />n<br />n<br />++ = Heavily doped<br />+= moderately doped<br />
  20. 20. Doping profile<br />n<br />n++<br />
  21. 21. Conventional ICs<br />An oxide-isolated npn bipolar transistor<br />Conventional npn transistor<br />From Muller and Kamins<br />
  22. 22. Forward active operating mode<br />n++<br />n<br />Electron injected: E -> B<br />Create excess concentration of minority carrier<br />Diffuse across the base region: B -> C<br />Electric field will swap the electrons into the collector.<br />
  23. 23. Minority carrier distribution <br />
  24. 24. Energy band diagram<br />

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