Concepts in Device Physics [Level 4] - Workspace

Concepts in Device Physics 2012 Course Syllabus and Recommended Resources 26 Lectures, Term 1 Aims This course was called “Device Physics” until 2010 has been extended since then to cover devices which utilise the magnetic properties of solids as well as optical and electrical devices which rely on semiconductors. The emphasis is not to cover variants of particular devices but rather to understand generic devices at a fundamental level. Each topic will be allocated six lectures, prefaced by eight lectures covering the relevant background material/themes and linking to the year three Solid State Physics (SSP) course.

Fundamentals (8 lectures) Karl Sandeman [email protected] This element of the course will revisit key concepts from the 3rd year solid state physics course as well as introducing some of the underlying themes relevant to the later part of the course. Electronic properties of matter including semiconductors Bandstructure, intrinsic and extrinsic semiconductors, electrons, holes and excitons. Direct and indirect gap materials; crystalline and amorphous materials. Drift, diffusion current and Einstein relation, Carrier generation/recombination, continuity equation. pn junction diode. Microscopic description of absorption Hamiltonian in the presence of electromagnetic radiation. Dipole approximation, dipole matrix element, quantum mechanical transition rate and absorption. Factors controlling absorption Quantum semiconductor heterostructures; quantum wells, tunnel junctions and superlattices Lattice constant and band gaps of common semiconductors; Type I, II and III heterostructures; Optical communication wavelengths and those available from heterostructures; Effective mass equation applied to QW; Density of states of a finite QW; Polarisation and selection rules; Magnetic properties of matter What is magnetism? The B-H or M-H hysteresis loop, coercivity, remanence and energy product. Magnetostatic energy and domains. Exchange: beyond Amperian currents: the origin of “J”. From Langevin to Weiss; paramagnetism and ferromagnetism in a mean field model. Ferromagnetism, antiferromagnetism, ferrimagnetism. Magnetic anisotropy: “Hard” and “soft” magnets.

Electronic Devices (6 lectures) Thomas Anthopoulos [email protected] This element of the course will cover the building blocks of microelectronics (metal-semiconductor contacts, transistors and logic gates), and materials and device concepts for future electronics. Metal-semiconductor contacts Surface properties of solids; clean and real surfaces; electron states in solids and at surfaces; the work function of a solid; types of metal-semiconductor contacts; contact interface states. Metal-oxide-semiconductor (MOS) capacitor Device structure; MOS equilibrium energy band diagram and voltage drop in MOS system, flat-band and nonflat-band conditions; accumulation layer and charge density; depletion, depletion width and voltage drop. Field-Effect Transistors (FETs) and the Bipolar junction transistor (BJT) The FET family tree; metal-oxide-semiconductor FET (MOSFET); MOSFET operation; gradual channel approximation and current-voltage characteristics; AC behaviour of MOSFET; thin-film transistors and their applications; History of BJT; device architecture and energy band diagram; basic operation of homo-junction pn-p and current gain; operating regimes and circuit configuration. Future transistor technologies Organic thin-film transistors (OTFTs); application of OTFTs in integrated circuits and optical displays; oxide semiconductors and their application in transparent electronics. Physics and technology of electronics manufacturing Manufacturing of integrated circuits and state-of-the-art applications.

Magnetic Devices (6 lectures) Will Branford [email protected] This element of the course will introduce students to the use of magnetic materials in information storage, data retrieval and concepts associated integrating storage and logic. Why magnetic devices? Most materials properties are functions of state: Composition and external forces acting on a material exactly describe it. To describe the polarization (magnetization) of a ferromagnetic material also requires knowledge of its history. History dependence allows data storage, enabling modern electronic products and multi-billion dollar industries. Control of properties with structure Ferromagnetism is spontaneous magnetization (usually) with a preferred direction (anisotropy). Magnetic Anisotropy has bulk, surface, interface and shape terms. Competition between external field and self-field energy terms leads to Hysteresis in M vs H. Stray and Demagnetizing fields result in “fictitious” magnetic charge. Domain behaviour and bits of information. Domain walls, single domain particles and superparamagnetism. Magnetic Data Storage Historic trends and the state of the art. Read and write mechanisms. Hard disks: scaling and the superparamagnetic limit. Perpendicular recording and patterned magnetic media. Integrating storage and logic: MRAM. Sensing Magnetism Magnetometers and magnetic imaging techniques. Electrical magnetic field detection. Magnetoresistance and Hall effect in non-magnetic materials. The Lorentz force and measurement geometry. Measurement sensitivity and carrier mobility. Inhomogeneity and nanostructured inclusions (EMR). Magnetoresistance in Ferromagnets Anisotropic, giant, colossal and tunnelling magnetoresistance. Intrinsic effects in FM materials, the Mott model of two independent spin currents. Transmission of spin currents across interfaces: heterostructures and superlattices. Applications in hard disk read heads: GMR and TMR spin valves. Current and Future Research in Magnetic Devices Magnetic nanoparticles for biomedical applications. Racetrack memory. Ferromagnetic semiconductors. Magnetic cooling. Frustrated magnets and monopoles. Photonic Devices (6 lectures) Amanda Chatten [email protected] This element of the course will cover the devices that involve the creation or detection of light and photovoltaics (including light emitting diodes, photodetectors, diode lasers and solar cells). Organic semiconductors Bonding in π conjugated molecules; Types of π conjugated molecule; Electronic states of π conjugated molecules; Absorption and emission spectra; Optoelectronic processes in molecular semiconductors Photodetectors Photodetector applications; p-n junction: regime of operation as a photodetector; Photodetector performance characteristics; Photodetector materials; p-n vs p-i-n photodetectors Solar Cells p-n junction: regime of operation as a solar cell ;solar cell characteristics; solar spectrum; short circuit current: limiting factors; open circuit voltage: limiting factors; Fill factor: l;imiting factors; solar cell design; PV materials; Limiting efficiency calculations; Multijunction cells; Organic solar cells Light emitting diodes and Organic LEDs p-n junction: regime of operation as a light emitting diode; radiative recombination; measures of LED efficiency; LED structure; LED materials. Organic LEDs: Factors controlling LED efficiency; Charge injection; Charge transport; Recombination; Exciton decay Lasers Factors affecting laser performance; QW laser profiles; Bulk heterostructure and quantum well lasers; In-plane versus surface emitting lasers; VCSEL structure and arrays; Laser structures: quantum dot lasers

Recommend resources General th C. Kittel, Introduction to Solid State Physics, 8 edn. (Wiley 2005) N. Ashcroft and N.D. Mermin, Solid State Physics (Saunders College Publishing) B. Tanner, Introduction to the Physics of Electrons in Solids (CUP) H.M. Rosenberg, The Solid State (OUP) More particular M.J. Cooke, Semiconductor Devices (Prentice Hall) S. Blundell , Magnetism in Condensed Matter (OUP 2001) M. Fox, Optical properties of solids (Oxford University Press, 2001, 13 copies in Central library) P. Yu and M. Cardona, Fundamentals of semiconductors: Physics and Materials properties (Springer, 1996, 1999, 2001, >10 copies) L. Solymar, Electrical properties of materials (Oxford University Press,1998, 11 copies) K. Barnham and D. Vvedensky (Eds.), Low-dimensional semiconductor structures : fundamentals and device applications (Cambridge University Press) J. Nelson, Physics of Solar Cells (Imperial College Press 2003).