Nano physics for semiconductors, great challenge

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1 Nano physics for semiconductors, great challenge Oleksandr Voskoboynikov 霍斯科 Phone: ext Office: 646 ED bld.4 Web:

2 In collaboration with: OUTLINE C.P. Lee NCTU, Taiwan C.M.J. Wijers TU, The Netherlands T. Chakraborty MU, Canada P. Pietilainen UO, Finland O. Tretyak KU, Ukraine and our students Semiconductor s in nano-physics. Why? Semiconductor nano-structures Nano for Semicondactor Spintronics Nano for Semiconductors Metamaterials Conclusions

3 BUT! Something to present myself: Originally I m from UKRAINE Ukraine is the second largest country in Europe after Russia. The total area of Ukraine is 603,700 sq. km (compare the area of France - 551,000 sq. km; Germany - 356,000; Great Britain - 244,000; Italy - 301,000; Spain - 505,000). The area spanned in a west-east direction is 1300 km; from north to south km. The population of Ukraine is 49,5 million (Germany - 78 million; France - 56 million; Great Britain - 58 million; Italy - 59 million; Spain - 40 million). Language - Ukrainian The average monthly temperature: in winter ranges from -8 to 2 C (17.6 to 35.6 F), while summer temperatures average 17 to 25 C (62.6 to 77 F).

4 Religion: Russian Orthodox Church and Ukrainian Orthodox Church in western Ukraine - Ukrainian Catholic (Uniate) Church The largest city in Ukraine is Kiev (Kyiv) the capital of Ukraine. Population more than 3 million people.

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8 Principal Academic Build Kiev University is named after Taras Shevchenko, a major figure in Ukrainian arts. Its reputation transcends the boundaries of Ukraine. Since the time of its foundation, 170 years ago, the University has been generating progressive ideas, shaping Ukrainian intellect, and providing champions of upheld national liberation activity in Ukraine. At present the student body of Kiev University totals about students

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11 Semiconductor s in nano-physics. Why? To provide with next generation of highly advanced semiconductor devices devices of the 21st century: Multi-Diapason LED s and Lasers, Nano-Photonics Devices, Single and Few Electron Devices, Nano-Magnets, Nano-sensors, Non-Volatile Massive Memory, Quantum CPU, New Spintronics Devices, etc.

12 Semiconductor s in nano-physics. Why?

13 Semiconductor s in nano-physics. Why?

14 Semiconductor s in nano-physics. Why?

15 Semiconductor s in nano-physics. Why?

16 Semiconductor s in nano-physics. Why? Future You decide and develop. Nano- is the interdisciplinary science and technology of the 21st Century. Combination of our present day knowledge and development in technology. is very promising. In this combination nano-physics plays indispensable role

17 NNI Budget Semiconductor s in nano-physics. Why? $1,600 $1,400 $1,200 $1,000 $800 $600 $400 $200 $ Year Total NSF

18 Semiconductor s in nano-physics. Why? trying to find a computer simulation of physics, seems to me to be an excellent program to follow out and I m not happy with all the analyses that go with just the classical theory, because NATURE ISN T CLASSICAL, dammit, and if you want to make a simulation of nature, you d better MAKE IT QUANTUM MECHANICAL, and golly it s a wonderful problem because it doesn t look so easy. (International Journal of Theoretical Physics, Vol.21, p. 486, 1981) computers with wires no wider than 100 atoms, a microscope that could view individual atoms, machines that could manipulate atoms 1 by 1, and circuits involving quantized energy levels or the interactions of quantized spins. There s Plenty of Room at the Bottom 1959 Annual Meeting of the American Physical Society

19 Semiconductor nano-structures Semiconductor Nano-Structures: nano scale 10-9 m ~10 nm Quantum Wells and wires Quantum Dots Quantum dot molecule Nano Rins

20 Semiconductor nano-structures Conduction band Valence band en n ~ Const( T ) as T 0 T Metals and semimetals n ~ e T0 T as T 0 T E Semiconductors and dielectrics g Ge Si GaAs GaN ev

21 Semiconductor nano-structures For instance: Doping is adding atoms to a material to change its electronic properties N-type silicon (phosphorous doped) contains free electrons P-type silicon (boron doped) contains free holes

22 Semiconductor nano-structures nano means quantum 1 mm mean free path in the quantum Hall regime 100 m mean free path in high mobility semiconductors at T< 4K 0.2 m commercial semiconductor devises nm de Broglie wavelength in semiconductors nm de Broglie wavelength in metals, inter-atomic distance From solid semiconductors to semiconductor nano-structures: Effects of size quantization : when the carrier motion in a solid is limited in a direction of a thickness of the order of the carrier de Broglie wavelength (or mean free pass, if this number is smaller) de Broglie wavelength : Room temperature operation requires a characteristic energy larger than the thermal energy kt = 25 mev ~l < 10 nm In semiconductors: at ten to hundred times larger than the lattice constant h p h 1.22 nm 3m kt E /[ ev] eff kin

23 Semiconductor nano-structures Confining the electron motion in at least one spatial dimension affects the energy levels and the density of states

24 Semiconductor nano-structures Quantum objects for the future of electronics: Quantum Wells/Wires/Dots/Dot-Molecules/Rings/Nano-Tubes. Usually use semiconductor material. Electron position is narrowly confined in 1, 2, or 3 dimensions, respectively. E between distinct energy states becomes large In quantum dots, total # of mobile electrons may be as small as 1!

25 Semiconductor nano-structures

26 Semiconductor nano-structures MBE technology Self-organization effects: Self-ordering or self-assembly During growth of strained heterostructures Compatible with present optoelectronic device technology III-V systems - InGaAs/AlGaAs, InP/InGaP Sb-containing systems - (In,Ga)Sb/GaAs Group III nitrides - (In,Ga,Al)N Ge/Si, SiO 2 /Si II-VI heterostructures

27 Semiconductor nano-structures InAs Quantum Dots on GaAs

28 Semiconductor nano-structures Applications Light emitting diodes Photovoltaics High density electronic memories High density optical memories Solid-state microcavity lasers Sensor protection elements Opto-electronic devices MEMS Photonic band gap devices Catalysis Waveguides & waveguide devices..

29 Nano for Semicondactor Spintronics a revolutionary new class of electronics based on the spin degree of freedom of the electron in addition to, or in place of the charge Conventional Electronics: Agent Electronic Charge Based on number of charges and their energy Performance limited in speed and dissipation Spintronics: Agent Electronic Spin Based on direction of spin and spin coupling Capable of much higher speed at very low power

30 Nano for Semicondactor Spintronics Main Agent Electronic Spin 1 In addition to their mass and electric charge, electrons have an intrinsic quantity of angular momentum called spin, almost as if they were tiny spinning balls. 2 Associated with the spin is a magnetic field like that of a tiny bar magnet lined up with the spin axis. 3 Scientists represent the spin with a vector. For a sphere spinning "west to east" the vector points "north" or "up. It points "down" for the opposite spin. 4 In a magnetic field, electrons with "spin up" and "spin down have different energies. 5 In an ordinary electric circuit the spins are oriented at random and have no effect on current flow. 6 Spintronic devices create spin-polarized currents and use the spin to control current flow.

31 Nano for Semicondactor Spintronics Main Agent Electronic Spin 1 In a conventional computer every bit has a definite value of 0 or 1. A series of eight bits can represent any number from 0 to 255, but only one number at a time. 2 Electron spins restricted to spin up and spin down could be used as bits. 3 Quantum bits, or qubits, can also exist as superposition of 0 and 1, in effect being both numbers at once. Eight qubits can represent every number from 0 to 255 simultaneously. 4 Electron spins are natural qubits: a tilted electron is a coherent superposition of spin up and spin down and is less fragile than other quantum electronic states. 5 Qubits are extremely delicate: stray interactions with their surroundings degrade the superposition extremely quickly, typically converting them into random ordinary bits.

32 Nano for Semicondactor Spintronics Classical bit 0 1 Quantum bit... n 2 0 1

33 Nano for Semicondactor Spintronics Magnetics Ferromagnets Photonics Electronics Optical Communication Information Storage Semiconductor Computation Logic

34 Nano for Semicondactor Spintronics Schematic diagram of the quantum computer based on the array of quantum dots. The spins of electrons confined in dots (quantum bits) are controlled by DC and AC electro-magnetic fields (after Loss and DiVincenzo )

35 Nano for Semicondactor Spintronics will lead to revolutionary advances in 21st Century photonics and electronics such as: Very high performance opto-electronic devices Very fast, very dense memory and logic at extremely low power Spin quantum devices like Spin-FETs, Spin LEDs and Spin RTDs Quantum computing in conventional semiconductors at room temperature Many other applications that we can t even envision now and..great Challenge for scientists

36 Nano for Semiconductors Metamaterials A meta material (or metamaterial) is an object that gains its material properties from its structure rather than inheriting them directly from the materials it is composed of. This term is particularly used when the resulting material has properties not found in naturally-formed substances. (Wilkepidia) In order for its structure to affect electromagnetic waves, a metamaterial must have structural features at least as small as (or smaller than) the wavelength of the electromagnetic radiation it interacts with. The nano-structured metamaterials are of a particular interest because they are promising for implementation of: Negative refractive index media in optical range Quantum computer with massive optical parallelism

37 Nano for Semiconductors Metamaterials From natural atoms to semiconductor nano-objects (artificial atoms) and from a bulk conventional material to a bulk metamaterial made from nano-objects Atoms Bulk conventional material Bulk metamaterial made from embedded nano-objects Quantum well Quantum nano-object (artificial atoms) Quantum wire Nano rings Quantum dots Quantum dot molecule

38 Nano for Semiconductors Metamaterials Left Handed Materials - negative refractive index --- V. Veselago (1968) n 0 0, 0 Recently we have demonstrated theoretically an opportunity to obtain simultaneously effective negative permittivity and permeability in optical range using metamaterials made from semiconductor nano-rings Schematic diagram of a composite material built from InAs/GaAs nanorings. a,,l << r ()/ r (0), r () (a) i (), i () (b) (10 15 Hz) (10 15 Hz) Effective permittivity and permeability of the system (a) Real parts of () and (); (b) normalized imaginary parts of () and () (Microelectronics Journal, 2005)

39 Nano for Semiconductors Metamaterials Nano-Photonics: Controlling the Electromagnetic Field Photonic crystal fabricated by the e-beam writer of the nano center in NCTU. Line defect waveguide

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41 Nano for Semiconductors Metamaterials Nano-based metamaterials operate at the interface of classical and quantum mechanical descriptions and require full knowledge of both to be developed. Great Challenge for scientists: - Multidisciplinary investigations to understand and control electrical, magnetic and magneto-optical properties of systems of semiconductor nano-objects combined in semiconductor nanostructured metamaterials.

42 Conclusions Semiconductor spintronics Optoelectronics based on semiconductor metamaterilas Semiconductor Spin-optronics (?)

43 Conclusions Nano physics operates with new (quantum) possibilities for information processing and storing Semiconductor spin electronics is the subject of increasingly intense study which to become an important research topic for 21 st century Semiconductor based metamaterials are promising for implementation of principally new media Much to be done. And this is a Great Challenge!