1. Nanoelectronics Part II Single-Electron and Few-Electron Phenomena and Devices Chapter 6 Tunnel Junctions and Applications of Tunneling 1Q.Li@Physics.WHU@2015.3

2. Consider a CNT is cut by AFM Q.Li@Physics.WHU@2015.32 AFM cut

3. Q.Li@Physics.WHU@2015.33 Creating a gap in CNTs

4. Q.Li@Physics.WHU@2015.34 In this chapter, we connect a quantum dot to wires via tunnel junctions, in order to form an electronic device such as a transistor

5. 6.1 Tunneling Through a Potential Barrier Q.Li@Physics.WHU@2015.35 123 From classical mechanics, for E > V 0, the particle will simply move past the potential barrier. (this is not the case for quantum mechanics.)

6. 6.1 Tunneling Through a Potential Barrier Q.Li@Physics.WHU@2015.36

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15. Q.Li@Physics.WHU@2015.315 This explains that, for gate leakage of MOSFET, as oxide thickness decreased, tunneling can become a significant problem.

16. Q.Li@Physics.WHU@2015.316 6.2 Potential Energy Profiles for Material Interfaces Modified work function of metal-SiO 2 Metal-Insulator

17. Metal-Semiconductor Q.Li@Physics.WHU@2015.317

18. Metal-Semiconductor Q.Li@Physics.WHU@2015.318 Schottky barrier

19. Metal-Semiconductor The depleted region is called a space charge layer, defined as W. This is called Schottky diode Ohmic contact: very little resistance in either direction (metal to semiconductor or semiconductor to metal.) Q.Li@Physics.WHU@2015.319

20. Metal-vacuum-metal junction Q.Li@Physics.WHU@2015.320

21. Metal-Insulator-Metal Q.Li@Physics.WHU@2015.321 Total potential energy

22. 6.3 Applications of Tunneling 6.3.1 Field Emission Q.Li@Physics.WHU@2015.322

23. 6.3.1 Field Emission Q.Li@Physics.WHU@2015.323 or (or called cold emission)

24. Q.Li@Physics.WHU@2015.324

25. 6.3.2 Gate-Oxide Tunneling and Hot Electron Effects in MOSFETs Q.Li@Physics.WHU@2015.325 In an ideal classical MOSFET, electrons do not travel between the channel and gate.

26. Hot Electrons and Fowler-Nordheim Tunneling Electrons is accelerated by the source-drain voltage. As they gain sufficient kinetic energy, they may tunnel through the oxide at the drain end. This is called hot-electron effect. Fowler-Nordheim Tunneling: if a strong gate voltage is applied, electrons will be energetic enough to tunnel through the oxide. Q.Li@Physics.WHU@2015.326

27. Hot Electrons Q.Li@Physics.WHU@2015.327

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29. Fowler-Nordheim Tunneling Q.Li@Physics.WHU@2015.329

30. Q.Li@Physics.WHU@2015.330 Direct tunneling vs. FN tunneling

31. 6.3.3 Scanning Tunneling Microscope Q.Li@Physics.WHU@2015.331 Gerd Binnig and Heinrich Rohrer (at IBM Zürich), the Nobel Prize in Physics in 1986. For an STM, good resolution is considered to be 0.1 nm lateral resolution and 0.01 nm depth resolution. (invented in 1981)

32. 6.3.3 Scanning Tunneling Microscope Q.Li@Physics.WHU@2015.332

33. 6.3.3 Scanning Tunneling Microscope Q.Li@Physics.WHU@2015.333

34. 6.3.3 Scanning Tunneling Microscope Q.Li@Physics.WHU@2015.334

35. 6.3.3 Scanning Tunneling Microscope Q.Li@Physics.WHU@2015.335 STM modes: (1) constant height, measure the tunneling current; (2) keep the current constant by varying the tip height. It can also be used to measure local DOS.

36. 6.3.4 Double Barrier Tunneling and the Resonant Tunneling Diode Q.Li@Physics.WHU@2015.336

37. Double Barrier Tunneling Q.Li@Physics.WHU@2015.337

38. Resonant Tunneling Q.Li@Physics.WHU@2015.338 0aa + L2a + L There are 8 unknowns: A, B, C, D, E, F, G and H There are 8 boundary conditions (4 boundary interface): ψ and dψ/dx are continuous across the boundary.

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41. Q.Li@Physics.WHU@2015.341 Resonant Tunneling

42. Q.Li@Physics.WHU@2015.342 1. Why we only see one peak at E 1, how about E 2 and E 3 ? 2. How to change E? Negative resistance

43. Resonant Tunneling Q.Li@Physics.WHU@2015.343

44. Resonant Tunneling Q.Li@Physics.WHU@2015.344

45. Resonant Tunneling The work of Leo Esaki, Ivar Giaever and Brian Josephson predicted the tunnelling of superconducting Cooper pairs, for which they received the Nobel Prize in Physics in 1973. While Dr. Esaki was involved in the development of a transistor with advanced high-frequency performance at Tokyo Telecommunications Engineering Corporation (currently Sony Corporation) in 1957, he discovered a phenomenon called a negative resistance: electric current decreases with the increase of voltage in a p-n junction for which a large amount of impurity is added. He proved that the phenomenon occurs by the jump of electrons from an n-type region to a p-type region, which is caused by a quantum-mechanical tunneling effect. The element developed by this phenomenon is called the Esaki-Diode and is applied to the microwave oscillation circuit. Q.Li@Physics.WHU@2015.345

46. Supperlattice Supperlattice is a periodic array of barriers. Q.Li@Physics.WHU@2015.346

47. Supperlattice In 1969, while working at the IBM Watson Research Center in the U.S., Dr. Esaki proposed an artificial material called semiconductor superlattice that has a periodic structure of layered semiconductors with different compositions. The concept of artificial superlattice proposed by Dr. Esaki opened up a new field in solid-state physics and made a major impact on the subsequent study. Q.Li@Physics.WHU@2015.347

48. 6.4 Main Points Quantum particle tunneling through a simple energy barrier Material junctions Field emission, applications to CNT Gate-oxide tunneling in MOSFETs: direct tunneling, FN tunneling, hot electron Principle of STM Tunneling through double barriers Idea of supperlattice Q.Li@Physics.WHU@2015.348 Try to work on all the problems: 6.1 – 6. 16. typical examples: 6.3, 6.11 and 6.12