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Solid State Devices

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Solid State Devices. Avik Ghosh Electrical and Computer Engineering University of Virginia Fall 2010. Outline. 1) Course Information 2) Motivation – why study semiconductor devices? 3) Types of material systems 4) Classification and geometry of crystals 5) Miller Indices.

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  1. Solid State Devices Avik Ghosh Electrical and Computer Engineering University of Virginia Fall 2010

  2. Outline 1) Course Information 2) Motivation – why study semiconductor devices? 3) Types of material systems 4) Classification and geometry of crystals 5) Miller Indices Ref: Ch1, ASF

  3. Course information Books Advanced Semiconductor Fundamentals (Pierret) Semiconductor Device Fundamentals (Pierret) Course Website: http://people.virginia.edu/~ag7rq/663/Fall10/ courseweb.html Grader:Dincer Unluer (dincer@virginia.edu)

  4. Distance Learning Info CoordinatorRita Kostoff, rfk2u@virginia.edu, Phone: 434-924-4051. CGEP/Collab Websites: https://collab.itc.virginia.edu/portal http://cgep.virginia.edu (UVa) http://cgep.virginia.gov (Off-site) http://ipvcr.scps.virginia.edu (Streaming Video) Notes: • Please press buzzer before asking questions in class • Email HW PDFs to dincer@virginia.edu or hand in class

  5. Texts

  6. References

  7. Grading info

  8. Grading Info • Homework - weekly assignments on website, no late homework accepted but lowest score dropped • Exams - three exams • Mathcad, Matlab, etc. necessary for some HWs/exams • Grade weighting: • Exam 1 ~20% • Exam 2 ~30% • Final ~30% • Homework ~20%

  9. ECE 663 Class Topics • Crystals and Semiconductor Materials • Introduction to Quantum Mechanics (QM101) • Application to Semiconductor Crystals – Energy Bands • Carriers and Statistics • Recombination-Generation Processes • Carrier Transport Mechanisms • P-N Junctions • Non-Ideal Diodes • Metal-Semiconductor Contacts – Schottky Diodes • Bipolar Junction Transistors (BJT) • MOSFET Operation • MOSFET Scaling • Photonic Devices (photodetectors, LEDs, lasers) Soft Cover Semiconductors Where can the electrons sit? How are they distributed? How do they move? Midterm1 Hard Cover Basic Devices Midterm2 Final

  10. Why do we need this course?

  11. Transistor Switches 1947 2003 A voltage-controlled resistor

  12. Biological incentives Transistors in Biology: Ion channels in axons involve Voltage dependent Conductances Modeled using circuits (Hodgkin-Huxley, ’52)

  13. Economic Incentives From Ralph Cavin, NSF-Grantees’ Meeting, Dec 3 2008

  14. A crisis of epic proportions: Power dissipation ! New physics needed – new kinds of computation

  15. We stand at a threshold in electronics !!

  16. How can we push technology forward?

  17. Better Design/architecture Multiple Gates for superior field control

  18. INSULATOR Silicon Nanowires Channel VG Organic Molecules VD Bottom Gate I Strained Si, SiGe Carbon Nanotubes Top Gate Drain Source Better Materials?

  19. SPINTRONICS Encode bits in electron’s Spin -- Computation by rotating spins GMR (Nobel, 2007) MRAMs STT-RAMs New Principles? QUANTUM CELLULAR AUTOMATA Encode bits in quantum dot dipoles BIO-INSPIRED COMPUTING Exploit 3-D architecture and massive parallelism

  20. Where do we stand today?

  21. Vd 20 µm 2 nm Vd Molecular Electronics Solid State Electronics/ Mesoscopic Physics “Top Down” … (ECE6163)

  22. Photolithography Top Down fabrication Top down architecture “Al-Khazneh”, Petra, Jordan (6th century BC)

  23. Bulk Solid (“macro”) (Classical Drift-Diffusion) Drain ~ 1023 atoms 80s ~ 106 atoms Clusters (“meso”) (Semiclassical Boltzmann Transport) Source Channel Bottom Gate Today ~ 10-100 atoms Molecules (“nano”) (Quantum Transport) Modeling device electronics ECE 663 (“Traditional Engg”) ECE 687 (“Nano Engg”)

  24. Vd 20 µm 2 nm Vd Molecular Electronics Solid State Electronics/ Mesoscopic Physics “Bottom Up” ... (ECE 687)

  25. Bottom up architecture Chepren Pyramid, Giza (2530 BC) ECE 587/687 (Spring) Full quantum theory of nanodevices • Carbon nanotubes, Graphene • Atomic wires, nanowires, • Point contacts, quantum dots, • thermoelectrics, • molecular electronics • Single electron Transistors (SETs) • Spintronics Build pyramidal quantum dots from InAs atoms (Gerhard Klimeck, Purdue) Bottom Up fabrication

  26. How can we model and design today’s devices?

  27. Need rigorous mathematical formalisms

  28. Calculating current in semiconductors I V Nonequilibrium stat mech (transport) • Drift-diffusion with Generation/ Recombination (Ch 5-6, Pierret) I = q A nv Quantum mech + stat mech • Effective mass, Occupation factors (Ch 1-4, Pierret)

  29. Calculating Electrons and Velocity • What are atoms made of? (Si, Ga, As, ..) • How are they arranged? (crystal structure) • How can we quantify crystal structures? • Where are electronic energy levels?

  30. Solids Metals: Gates, Interconnects

  31. Solids tend to form ordered crystals Natural History Museum, DC (Rock salt, NaCl)

  32. Describing the periodic lattices

  33. Bravais Lattices Courtesy: Ashraf Alam, Purdue Univ Each atom has the same environment

  34. 2D Bravais Lattices Courtesy: Ashraf Alam, Purdue Univ Only angles 2p/n, n=1,2,3,4,6 (Pentagons not allowed!)

  35. Epitaxial growth by vapor deposition of CO/hydroC on metals (Rutter et al, NIST) Chemical Exfoliation of HOPG on SiO2 (Kim/Avouris) 2D non-Bravais Lattice – e.g. Graphene • Missing atom  not all atoms have the same environment • Can reduce to Bravais lattice with a basis

  36. Irreducible Non-Bravais Lattices MC Escher “Quasi-periodic” (Lower-D Projections of Higher-D periodic systems) Early Islamic art Penrose Tilings

  37. Not just on paper... 5-fold diffraction patterns Pentagons ! (5-fold symmetry not possible in a perfect Xal) MoAl6 FeAl6 (Pauling, PRL ’87)

  38. Pentagons allowed in 3D Buckyball/Fullerene/C60

  39. 3D Bravais Lattices 14 types

  40. Describing the unit cells

  41. Simple Cubic Structure Coordination Number (# of nearest nbs. = ?) # of atoms/cell = ? Packing fraction = ?

  42. Body Centered Cubic (BCC) Mo, Ta, W CN = ? # atoms/lattice = ? Packing fraction?

  43. Face Centered Cubic (FCC) Al,Ag, Au, Pt, Pd, Ni, Cu CN = ? #atoms/cell = ? Packing fraction = ?

  44. Diamond Lattice C, Si, Ge a=5.43Å for Si CN = ? Packing fraction = ? Two FCC offset by a/4 in each direction or FCC lattice with 2 atoms/site

  45. Web Sites That may be helpful http://jas.eng.buffalo.edu/education/solid/unitCell/home.html http://jas.eng.buffalo.edu/education/solid/genUnitCell

  46. Zincblende Structure III-V semiconductors GaAs, InP, InGaAs, InGaAsP,…….. For GaAs: Each Ga surrounded By 4 As, Each As Surrounded by 4 Ga

  47. Only other type common in ICs Hexagonal Lattice Al2O3, Ti, other metals Hexagonal

  48. Crystal Packing: FCC vs HCP X X X X X X

  49. Semiconductors: 4 valence electrons • Group IV elements: Si, Ge, C • Compound Semiconductors : III-V (GaAs, InP, AlAs) II-VI (ZnSe, CdS) • Tertiary (InGaAs,AlGaAs) • Quaternary (InGaAsP)