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Linear Model for Diode; E L 7 6 D ELETRÔNICA APLICADA À ENGENHARIA MECÂNICA MICROELETRÔNICA: -Semicondutores; -Diodo Semicondutor. Aula 02 (10.mar.2020) MICROELETRÔNICA Dmitri Ivanovic MENDELEIEV (1834-1907) • CLASSIFICAÇÃO PERIÓDICA • SEMICONDUTORES • APLICAÇÃO NA ELETRÔNICA • ESTRUTURA CRISTALINA • PORTADORES DE CARGA • BANDAS DE ENERGIA • DOPAGEM MICROELETRÔNICA MICROELETRÔNICA Source: < https://www.coop.com.au/periodic-table-of-elements-reference-card-chm001/5555000095488 > MICROELETRÔNICA ELEMENTARY CONCEPTS • Atomic Models Philosophical → Democritus; Lavoiser; Dalton; Avogadro, Brown Subatomic particles → Thomson (“plum-pudding”), Rutherford; Bohr Quantum mechanics → Werner Heisenberg -19 • Elementary charge → qe = -1,6x10 [C] -31 • Electron mass → me = 9,1x10 [kg] • Electron radius → 10-15 [m] • Atom radius → 10-10 [m] MICROELETRÔNICA THE STRUCTURE OF MATTER - Dalton; - Thomson; - Rutherford-Bohr; - De Broglie (modelo quântico). MICROELETRÔNICA THE NATURE OF THE ATOM Dalton’s Atomic Theory Fonte: < https://www.youtube.com/watch?v=rxltY8HhQkA > DISCUSSIONS ABOUT DALTON´s ATOMIC THEORY • Innovatively: • Setbacks: MICROELETRÔNICA JOSEPH JOHN THOMSON´s ATOMIC THEORY Thomson's Model of an Atom - Class 9 Tutorial Fonte: < https://www.youtube.com/ watch?v=lLwnACfo7hY > DISCUSSIONS ABOUT THOMSON´s ATOMIC THEORY • Innovatively: • Setbacks: MICROELETRÔNICA ELECTRONIC STRUCTURE OF THE ELEMENTS (RUTHERFORD) Rutherford's Model of an Atom(US accent) Fonte: < https://www.youtube.com/watch?v=XLaeFUKd2Y4 > DISCUSSIONS ABOUT RUTHERFORD´s ATOMIC THEORY • Innovatively: • Setbacks: MICROELETRÔNICA THE ENERGY-BAND THEORY (BOHR) Bohr Model of the Hydrogen Atom, Electron Transitions, Atomic Energy Levels, Lyman & Balmer Series Fonte: < https://www.youtube.com/watch?v=mXxsT1ut35Q > DISCUSSIONS ABOUT BOHR´s ENERGY-BAND THEORY • Innovatively: • Setbacks: MICROELETRÔNICA DE BROGLIE AND THE QUANTUM MODEL Louis de Broglie's explanation of Bohr's atomic model Fonte: < https://www.youtube.com/watch?v=oLd-6UytkIU > DE BROGLIE AND THE QUANTUM MODEL everything is almost set, but nowadays… FURTHER DIVING IN THE ATOMIC SCIENCE (With Tyler DeWitt) Fonte: < https://www.youtube.com/watch?v=NSAgLvKOPLQ > Model of atoms timeline See more at < http://socratic.org/chemistry > Major discoveries about atom´s structure were performed with study of gases. But, what about the other states of matter? Let us take a look… HISTORY CURIOSITY 1.869 – CROOKES (William) and others, invented the Electrical Discharge Tube. Source: < https://en.wikipedia.org/wiki/File:Crookes_tube_two_views.jpg > HISTORY - CURIOSITY 1.897 – THOMSON (Joseph John) discovered the electron. Curiosity: in 1.906, Thomson was awarded with the Nobel Prize in Physics. Source: < https://en.wikipedia.org/wiki/Karl_Ferdinand_Braun > STATES OF MATTER (*) - Gases; - Liquids; - Solids; - Plasma. (*) Classical states – see next... FURTHER STATES OF MATTER (**) - BOSE-EINSTEIN Condensate (BEC); - Neutron-degenerate matter; - Quark-gluon plasma. (**) Non-classical states ... AND FURTHER MORE - Glass; - Plastic Crystal; - Liquid Crystal states; Also non-classical states - Magnetically ordered; - Microphase-separated; - Superfluid; - Fermionic condensate; - Rydberg molecule; Low-temperature states - Quantum Hall state; (VALIGRA, 2005; MINKEL, 2009) - Photonic matter; - Dropleton; - Degenerate matter; High-temperature states - Quark matter; (FOWLER, 1926; OPPENHEIMER, 1939) - Color glass condensate; - Superglass; - Supersolid; Proposed (MURTHY et. al., 1997) - String-net liquid. Don´t worry at which state you found the matter!!! See? It´s all about GASES Atoms are highly energized and therefore, much room is there for relative movement (i.e., vibration) between them. LIQUID At liquid state, atoms are at an intermediate energized point. There is a plenty room to their vibration, however, they are much more condensed than in gases. SOLID At solid state, atoms are very, very condensed. There is low enthalpy of the containment system. For all intents and purposes, one can say that only tiny limited atom vibration is allowed (*). PLASMA Maybe the plasma is the most abundant state of matter in universe although not so abundant in our planet. There is very high enthalpy allowing their atoms become ionized. ... fleetingly ELECTRICAL NATURE OF MATTER Early experiments: 1. Static electricity (ancient Greece); 2. FARADAY´s unveil (XIX b.C); 3. Conduction of electricity through gases (THOMSON and others). ELECTRICAL NATURE OF MATTER Although there are electrical charges at matter constituints, conventioned “positive” and “negative”, the matter itself is NEUTRAL. Even so, how can the electricity occur? ELECTRICAL NATURE OF MATTER The answer, my friend, is NOT blowing in the wind: Faraday´s studies of electrolysis. Faraday was an excellent experimentalist. Doing so, he early realized that, in particular conditions, external energy could be applied to an environment of electrolysis, causing changes in the distribution of electrical charges. Todays´authors (MILMANN, 1972, p.5) use the terms: “Nature of the atom”. ELECTRICAL NATURE OF MATTER Since the matter can exist in any state, it is reasonably state that: Convenient energy exciting an atom can turn possible the movement of electron (negative charge) leading it to that an orbit that allows electricity to flow. Doing so, Regard this view, elements can be stated as: CONDUCTORS NON-CONDUCTORS (“insulators”) ELECTRICAL NATURE OF MATTER For example: Carbon, Silicon, Germanium, Tin and Lead Although these 5 materials are classified at IVA-Group on Periodic Table of Elements, one can notice that: • Carbon in its allotropic form “diamond” is non-conductor; • Tin and Lead are both electricity conductors; • Silicon and Germanium are not as good conductors as Sn and Pb. However, they are not electricity insulators. ELECTRICAL NATURE OF MATTER CHALLENGE: Acting like your predecessors in scientific experiment, state the properties of “stibium”, Te and Po. THE ENERGY-BAND THEORY Elements like Silicon, Germanium and Arsenic are called “metalloids”, since they occur in environment like crystals(*) and at solid state like majority of metals. Despite this property, they are not as good conductors of electricity and termal energy as metals are. (*) CRYSTAL is a term used in chemistry to designate a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions (ASHCROFT; MERMIN, 1976). THE ENERGY-BAND THEORY Contrary to that seemed at gases, where the atoms are sufficiently far apart not to exert any influence on one another, the electric potencial for a crystal is a periodic function in space, whose value at any point is the result of contributions from every atom in a crystal structure. (graphite) (diamond) (steel) (glass) THE MILLER INDEX When studying crystals, the crystallographic directions are fictitious lines linking nodes (atoms, ions or molecules) of a crystal. Similarly, the crystallographic planes are fictitious planes linking nodes. Some directions and planes have a higher density of nodes. These planes have an influence on the behaviour of the crystal: 1. optical properties; 2. adsorption and reactivity; 3. surface tension; 4. dislocations (plastic deformation). (ASHCROFT; MERMIN, 1976, p.135-44) THE MILLER INDEX Silicon and Germanium tetrahedral crystal structure (BOYLESTAD, NASHELSKY; 1999) THE ENERGY-BAND THEORY In consequence of this observation, when atoms form crystals, the inner-electronic shell (see BOHR atomic model) are poorly affected. However, the outter-shell electrons are dramatically affected, since they are shared by multiple atoms in a crystal. So, there are new values energy associated in comparision to same electron in a gas. (MILMANN, 1972, p.15) METALS, METALLOIDS, CONDUCTORS, INSULATORS AND SEMICONDUCTORS An excellent conductor of electricity is called a METAL. A very poor conductor of electricity is called an INSULATOR. Finally, a substance whose conductivity lies between these extremes materials is called a SEMICONDUCTOR(*). Depending upon its energy-band structure, the materials used in this subject can be placed in one of these three classes (see below). (BOYLESTAD, NASHELSKY; 1999, p.16) SEMICONDUCTORS According to MILMANN, a SEMICONDUCTOR is a substance which -19 EG (band gap) has at magnitude of about 1 [eV] (i.e., 1,6x10 [J]) at stated temperature. As a matter of fact, according BOYLESTAD: OBS.: MILMANN considers graphite as a semiconductor. However, band gap for this allotropic form of Carbon is about 0,03 [eV] at room temperature. Hence one must assume that graphite is a conductor!!! (MILMANN, 1972, p.17) SEMICONDUCTORS Some semiconductors are most commonly used in construction of electonic devices (BOYLESTAD, 2013). Singular crystal: i. Ge: in 1939, just after the invention of semiconductor diode, germanium was the first material applied. It occurs in nature bonded to oxygen and it is the 50th element in the Earth´s crost. ii. Si: it is very abundant in nature but only was applied in construct electronic devices after its refine was developed. SEMICONDUCTORS Compound crystal: i. GaAs ii. CdS iii. GaN iv. GaAsP All of above are made by two or more semiconductor materials of diferent atomic structures. SEMICONDUCTORS LET US NOW TAKE A LOOK AT SOME DEFINITIONS... SEMICONDUCTORS COVALENT BOND It is stated that a covalent bond occurs when atoms share their electrons at valence layer. Silicon singular crystal GaAs compound crystal (BOYLESTAD, NASHELSKY;
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