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Quantum wells,Quantum wires and Quantum Dots


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Effect of the quantum confinement

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Quantum wells,Quantum wires and Quantum Dots

  1. 1. Quantum wells,Quantum wires and Quantum dots Presented By_ To_ Sanjeeb Limbu(Reg.No:14305019) Dr.A.Subramania Sir M.Tech.-Nanoscience & Technology Associate Professor(CNST)
  2. 2. Introduction When the size or dimension of a material is continuously reduced from a large or macroscopic size, such as meter or centimetre to a very small size, the properties remain the same at first then small change begin to occur, until finally when the size drops below 100 nm. In this way formed a new structure of the material is called nanostructure. The wells, wires and dots are nothing but nanostructure of the material. The nanostructure are explain through the quantum mechanics so is called quantum wells, quantum wires and quantum dots. Its not a classical wells, wires and dots. Its also called low dimensional structure.
  3. 3. Classification of law dimensional materials 1.Three dimensional (3D) structure or bulk structure: No quantisation of the particle motion occurs i.e., the particle is free. Electron in conduction band and holes in valence band are free to move in all three dimensions of space. Eg.cube
  4. 4. 2.Two-dimensional (2D) structure or quantum well: Quantum confinement in nanostructure-Ifone dimension is confined or reduced to the nanometre ranges while other two dimensions remain large then we get a structurecalled quantum well. Eg.nano wires,nanorod,nanotube. Electrons confined in one direction Quantum wells (Thin films) : Electrons can easily move in 2 dimensions (One dimensional quantisation) kx ky nz
  5. 5. 3.One-dimensional (1D) structure or quantum wire: If two dimensions are reduced in to the nanometre range and remain large the structure to as a quantum wire. Eg.nanoseed (Graphene) Electron confined in 2 dimensions Quantum wires: Electron can freely easily move in 1 dimension. (2 dimensional quantisation) The semiconductor wires surrounded by a material with large band gap .Surrounding material confines electron and hole in two dimensions(carrierscan only move in one dimensions) due its larger bandgap.Radius of quantum wires,nanorods and nano tube, nano pillars (1D structures)1-100 nm range (Typical nano- scale dimension) kx nz ny
  6. 6. 4.Zero-dimensional (0D) structure or quantum dot: The extreme case of this process of size reduction in which all three dimensions reach the low nanometre range is called a quantum dot. Eg. Nano dot Electron confined in three dimensions Quantum dot: electron can easily moves in zero dimensions. (3 dimensional quantisation) Electron and holes are confined in all the three dimensions of space by a surrounding material with a larger band gap Discrete energy levels(artificial atoms) No quantum dots has a larger band gap like bulk semiconductor. Typical dimensions: 1-10 nm ny nz nx
  7. 7. Comparison of Nanostructure: Progressive generation of rectangular nanostructures. Progressive generation of curvilinear nanostructures.
  8. 8. Density of states: The density of states of a system describes the number of states per interval of energy of each energy level that are available to be occupied by electrons. Density of states moving from the bulk(3D) crystal to a quantum well(2D) ,there is a further change in the density of on moving quantum wires(1D) and quantum dots(0D), dE dk dk dN dE dN DoS  Structure Degree of Confinement Bulk Material 0D Quantum Well 1D 1 Quantum Wire 2D Quantum Dot 3D d(E) dE dN E E1/
  9. 9. Quantum wells are formed in semiconductors by having a material, like gallium arsenide sandwiched between two layers of a material with a wider band gap, like aluminium arsenide. (Other example: layer of indium gallium nitride sandwiched between two layers of gallium nitride ) These structures can be grown by molecular beam epitaxy or chemical vapor deposition with control of the layer thickness down to monolayer's. How to prepare a quantum well ???
  10. 10. Application of quantum wells: In optical devices such as laser diodes .Formed by semiconductor materials quartz and silica(Absorb/Emit light)efficiently). They are also used to make HEMTs (High Electron Mobility Transistors), which are used in low-noise electronics.(HeterostructureFET) Quantum well infrared photo detectors are also based on quantum wells, and are used for infrared imaging (Absorb photons)
  11. 11. How to prepare a quantum wire ???
  12. 12. How to prepare a quantum wire ??? a) The most important application of nanowires in nanoelectronics is using them as junctions or as multi-segment nanowires or crossed nanodevices. b) Quantum wire is used in energy storagedevices
  13. 13. How to prepare a quantum dot ???
  14. 14. Application of quantum dots: Photovoltaic devices: solar cells Biology : biosensors, imaging Light emitting diodes: LEDs Quantum computation Flat-panel displays Memory elements Photo detectors Lasers
  15. 15. References:  Introductionto Nanotechnology,ChgarlesP.Poole,Jr Quantumwells, Quantum wires and Quantum dots ,Paul Harrison Solid-State Electronics 44 (2000) 2207-2212 JACS Communications PHYSICALREVIEW LETTERS Quantum Wells, Quantum Wires, Quantum Dots, Quantum Limit of Conductance, Quantum Capacitance & Quantum HALL Effect,R. John BoscoBalaguru,B. G. Jeyaprakash