Preparation of semiconductor nanomaterials

Transkript

1 Studijní program:nanotechnologie Studijní obor: Nanomateriály (organizuje prof. J. Šedlbauer, FPP TU v Liberci) Preparation of semiconductor nanomaterials 2014/2015 (prof. E. Hulicius, FZÚ AV ČR, v.v.i.,)

2 9. a 10. Semiconductor (nano)hetero-structures and devices. Semiconductor heterostructures, exploitation of quantum-size properties of nanostructures, reasons of implementation, materials. Understanding of specifics of quantum-size structures and devices will be important for students pretending for better classification. Specifics of quantum-size device properties will be subject of questions.

3 Semiconductor heterostructures, using of quantum-size properties of nanostructures, reasons of implementation, materials, future improvements Semiconductors, monocrystals not only, but mainly Why does crystal exist? Crystal lattice and properties (electrical, optical, (mechanical not here)) Role of defects? Types of defects, their concentration, influence on devices. (point defects, dislocations, stacking faults, twins,...)

4 Bravais lattices It is possible to prove that only 14 different Bravais space lattices does exist. See table: Crystal system krystalová soustava Triclinical triklinická (trojklonná) Monoclinical monoklinická (jednoklonná) Orthorhombic ortorombická (rombická, kosočtverečná) Tetragonal tetragonální (čtverečná) Cubic kubická (izometrická) Hexagonal hexagonální (šesterečná) Trigonal trigonální (romboedrická, klencová) Minimal symmetry minimální symetrie No žádná One double foliate axe along c jedna 2četná osa podél c Three double foliate axes along a, b, c tři 2četné osy podél a, b, c One four foliate axe along c jedna 4četná osa podél c Four triple foliate axes along cube body diagonal čtyři 3četné osy podél tělesových úhlopříček krychle One six foliate axe along c jedna 6četná osa podél c One triple foliate axe along axe of hexagonal cell jedna 3četná osa podél osy hexagonalní buňky

5 Crystal lattice, electron and hole band energy structure High-school band structure, bands in k -space, (Brillouin zone, direct and indirect semiconductors, p-n junction, heterostructure, quantum well, density of electron states). Band structure of Si and GaAs

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7 Crystal lattice, electron and hole band energy structurer High-school band structure, bands in k -space, (Brillouin zone, direct and indirect semiconductors, p-n junction, heterostructure, quantum well, density of electron states). State exam questions at FEL-CVUT:

8 Principles of electronic devices Jevy v polovodičích: Pásová struktura polovodičů, hustota stavů, efektivní hmotnost, přímý a nepřímý polovodič. Statistika elektronů a děr ve vodivostním a valenčním pásu, Fermiho hladina, vliv příměsí. Poissonova rovnice, rovnice kontinuity, difúzní a vodivostní proud, pohyblivost. Boltzmanova kinetická rovnice, rozptylové mechanismy. Generační a rckombinační mechanismy, doba života, difúní rovnice. Přechod p-n: oblast prostorového náboje, rozložení koncentrace nositelů náboje, intenzity elektrického pole, potenciálu, difúzní napětí, Shockleyho rovnice VA charakteristiky, injekce a extrakce nositelů náboje, injekční účinnost. Bariérová a difúzní kapacita. Průraz tunelový, lavinový, jejich teplotní závislost. Heteropřechody, rozměrové kvantování, elektron v kvantové jámě, hustota stavů v 2D, 1D a OD polovodiči, rezonanční tunelování, transport elektronů v supermřížce. Dioda, výkonová dioda PIN, varikap, Zenerova dioda, tunelová dioda. Kontakt kov-polovodič - kvalitativní popis dějů v: usměrňující a neusměrňující kontakt, VA charaktcristika, Schottkyho dioda. Propustné a závěrné vlastnosti, porovnání s pn přechodem. Teplotní vlastnosti. Struktura MIS - kvalitativní popis dějů ve: slabá a silná inverze, pásový modely, reálná struktura MIS, vliv náboje v oxidu a na rozhraní. Bipolární tranzistor: funkce, zbytkové proudy, průrazné napětí, charakteristiky, zapojení SB, SC, SE a jejich vlastnosti, ss pracovní bod a jeho nastavení, parametry h a y, náhradní obvody, kmitočtové a teplotní vlastnosti. Spínací aplikace. Vliv povahy zátěže, první a druhý průraz. Unipolární tranzistor: JFET. MESFET, MOSFET, DMOS. Indukovaný a zabudovaný kanál. Vlastnosti, charakteristiky, parametry. Základní zapojení, ss pracovní bod a jeho nastavení, parametry, kmitočtové a teplotní vlastnosti. Jevy krátkého kanálu MOSFET.

9 Vícevrstvé součástky: diak, tyristor, charakteristiky a parametry. GTO. Optoelektronické součástky: Fotoelektrický jev, fotovodivost, spontánní a stimulovaná emise, absorpce. elektroluminiscence, katodoluminiscence. Optické vláknové a planární vlnovody: princip funkce, materiálově-technologické řešení, základní vlastnosti. Polovodičové zdroje záření a detektory: princip funkce, materiálové a konstrukční řešení, základní vlastnosti a parametry. Optické přenosové systémy: základní principy, konstrukční komponenty, dosahované parametry. Optické vláknové senzory: základní principy, vlastnosti. Vysokofrekvenční a kvantově vázané polovodičové součástky - principy činnosti, aplikace: RTD, MESFET, HEMT - modulační dotace, HBT, HET - překmitový jev, jednoelektronový tranzistor- Coulombovská blokáda, laser s kvantovou jámou, polovodičový fotonásobič. Šum (typy, š. pasivní součástky, přechodu PN, FET, BJT). Modely součástek statický, pro malý, velký signál, nf., vf. včetně základních modelů používaných v simulačních programech. Trendy technologie submikronových integrovaných obvodů na křemíku, pokroky ve zvyšování hustoty, integrace ULSI, GSI. Ultrafialová, rentgenová, elektronová, iontová litografie. Konstrukce submikronového tranzistoru - potlačení jevu krátkého kanálu a horkých elektronů. Technologie propojování a víceúrovňové metalizace. Multičipové moduly. Jazyky HDL. Prostředky syntézy: simulace a verifikace návrhu IO. Pasivní součástky diskrétní a integrované. Základní konstrukce a parametry. Frekvenční a teplotní vlastnosti. Mikrosystém, mikrosenzor a mikroaktuátor - charakteristické vlastnosti (citlivost, nelinearita, atd.), principy činnosti (elektrostatické, piezoelektrické, magnetické, tepelné, optické, mechanické. atd.).

10 Suitable and used elements, compounds and materials Elementary semiconductors: silicon, silicon, silicon, (also germanium, selenium, diamond), but... They have indirect junctions, forbidden gap (E g ) and refraction index (n) is changeable only small. Compounds semiconductors: A III B V - GaAs, InP, GaSb,... A II B VI - CdTe, CdSe,... A IV B IV -GeSi, A III X B III (1-X) C V -AlGaAs, A III X B III (1-X) C YV D V (1-Y) - GaInAsSb,

11 Elements and compounds

12 Compound semiconductors II.B III.A IV.A V.A VI.A 2 B C N O 3 Al Si P S 4 Zn Ga Ge As Se 5 Cd In Sn Sb Te 6 Hg Tl Pb Bi Po

13 Dependence of E g and absorption edge on the lattice constant:

14 Forbidden gap dependence on lattice constant for some other materials

15 Repetition general information about: Band structure: If you are familiar with this subject, you can jump over.

16 Creation of band structure

17 Band structure in k-space: První aproximace poruchového počtu, bez započtení spinorbitální interakce První aproximace poruchového počtu, se započtením spinorbitální interakce Druhá aproximace poruchovéh počtu, se započtením spinorbitální interakce

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19 Structures, heterostructures, nanostructures and peculiarities (material engineering) Homogenous structures P-N junctions: Electronics is based on them. Few interesting, simple, cheap, efficient device examples: - LEDs based on GaAs:Si amphoteric doping; - semiconductor solar cells (mainly Si); Semiinsulating on highly conductive layer and vice versa. Bulk crystal separation layer (epitaxial buffer) function epitaxial layer - (gradual improving crystallographic quality) Monocrystal - polycrystalline amorphous layer or vice versa.

20 Heterogenous structures (heterostructures) - clasical" Not only heterosturctures with P-N junctions, there are use homo-heterostructures with Eg junctions or fluent changes of forbidden gaps, refraction index with strong improvement of device parameters. Figures from Scientific American at 1971!! Obr Junctions type I., II. (a III.). Obr Strained junctions. Obr

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23 Heterogenous structures (heterostructures) - clasical" Not only heterostructures with P-N junctions, there are use homo-heterostructures with Eg junctions or fluent changes of forbidden gaps, refraction index with strong improvement of device parameters. Figures from Scientific American at 1971!! Junctions type I., II. (a III.). Obr Strained junctions. Obr

24 Heterojunctions: (a) = b the first type (b) = a the second type (c) - the thirt type

25 Examples of the first type heterostructures can be different

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28 Heterogenous structures (heterostructures) - clasical" Not only heterosturctures with P-N junctions, there are use homo-heterostructures with Eg junctions or fluent changes of forbidden gaps, refraction index with strong improvement of device parameters. Figures from Scientific American at 1971!! Junctions type I., II. (a III.). Strained junctions. Obr

29 Strained and relaxed lattice

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32 Quantum- size structures Nano(hetero)structures - quantum" Decreasing of one or more dimension spaces in the structure to the level comparable with wavelength of electron (from tenths (0.1s) to tens (10s) nanometres (nm)) Quantum wells Quantum wires Quantum dots Figs We can create new artificial types of band structures - superlattices (explanation difference between superlattice and multiple quantum well), quantum cascade lasers.

33 Density of electron energy states

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37 Peculiarities" - Solving of troubles of Type II heterojunctions - QD InAs in GaAs on Si - Fullerenes (also buckyballs C 60, 90, 80 (According architect R. Buckminstera Fullera who proposed and created similar dome buildings.) - Quantum cascade lasers - Nanocoils - Spinotronics

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39 Peculiarities" - Solving of troubles of Type II heterojunctions - QD InAs in GaAs on Si - Fullerenes (also buckyballs C 60, 90, 80 ) (According architect R. Buckminstera Fullera who proposed and created similar dome buildings.) - Quantum cascade lasers - Nanocoils - Spinotronics

40 QD InAs/GaAs na Si

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46 Základní způsoby generace záření ve (střední) infračervené oblasti

47 Tunable Emission Over a Wide Spectral Range Conduction band schematic of GaInAs/ AlInAs quantum cascade laser lattice matched to InP. Cross sectional schematic of laser waveguide structure. Photograph of a self-contained prototype quantum cascade laser pointer realised at CQD. Demonstrated single mode emission from quantum cascade lasers spanning both atmospheric windows.

48 M. Razeghi, Center for Quantum Devices, Northwestern Univ., Evanston Uncooled Infrared (5-12 m) Quantum Cascade Lasers Lasers operating in the mid- and far-infrared (5-12 m) spectral region are desirable for many applications. Up until recently, the only such laser technologies available were based on bulky gas or solid-state lasers as well as cryogenically cooled semiconductor lasers. One of the most exciting projects at the Center for Quantum Devices (CQD) is uncooled infrared quantum cascade lasers (QCLs), which, being a semiconductor laser, is inherently compact and will help eliminate the need for bulky and unreliable cryogenic cooling. This translates to a smaller, cheaper, system with a longer lifetime and less maintenance. Besides our current records with respect to threshold current density and high peak power, we have recently demonstrated the highest power continuous wave QCLs at room temperature.

49 Distributed Feedback (DFB) Quantum Cascade Lasers

50 High Performance Lasers Operating at Room Temperature 75 period waveguide core Cavity: 3 mm x 25 m Cross section image of a buried-ridge QCL laser. Cross section image of a Au electroplated QCL. Electrical and optical characteristics of a typical 9 m quantum cascade laser operating in pulsed mode at room temperature. Peak output power of 2.5 W is the highest power for a quantum cascade laser in these conditions.

51 Highest average power QCL. Comparison of groups >4 m

52 M. Razeghi, Center for Quantum Devices, Northwestern Univ., Evanston Uncooled Infrared (5-12 m) Quantum Cascade Lasers Lasers operating in the mid- and far-infrared (5-12 m) spectral region are desirable for many applications. Up until recently, the only such laser technologies available were based on bulky gas or solid-state lasers as well as cryogenically cooled semiconductor lasers. One of the most exciting projects at the Center for Quantum Devices (CQD) is uncooled infrared quantum cascade lasers (QCLs), which, being a semiconductor laser, is inherently compact and will help eliminate the need for bulky and unreliable cryogenic cooling. This translates to a smaller, cheaper, system with a longer lifetime and less maintenance. Besides our current records with respect to threshold current density and high peak power, we have recently demonstrated the highest power continuous wave QCLs at room temperature.

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57 Using a combination of different materials to prepare useful functional devices (transistors, LEDs and lasers, detectors and photovoltaic cells,...) with better parameters. It is possible to prepare new materials desirable properties like complicated ternaries or quaternaries non existing in the nature. It is possible to use combination of thin binaries instead of chemistry of non existing ternaries with better properties. We can construct structures and devices (mainly on nanostructure base) with new properties (superlattices, quantum cascade lasers (QCL), molecular electronics, nanorobots, devices with quantum wells, wires, dots, with photonic crystals, with photo-electrochemical cells, etc). (In this lectures there were not described nonsemiconductor structures, biological nanostructures, Au, Ag, Fe, TiO, ZnO nanoparticles with huge application fields, nanofibres, nanomechanics, nanocolours, nanotextile also with great application potential.)

58 Structures for devices based on nonclasical (nonintuitive) quantum physical effects Examples of nano-hetero-structures and heterodimensional structures for later described devices.

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60 Heterodimensional Device Technologies Interfaces between differentdimensional structures.

61 Examples of devices based on nonclasical (nonintuitive) quantum physical effects May be the oldest one is tunnel diode. It is based on resonant tunnelling. Obr. HEMT transistors and other, e.g. one electron transistors. Obr. Quantum etalon of resistivity (ohm normal) is based on quantum Hall effect. Project MÚ, FEL a FZÚ (P. Svoboda) Semiconductor lasers and LEDs in general (and with QW and QD especially). Next lecture on gradual and abrupt improving of their parameters when nanostructures are used.

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68 Kvantový normál odporu

69 Quantum etalon of resistivity (ohm normal)

70 Quantum normal of resistivity (ohm unit)

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73 Thank you for your attention

74 Next: LED Light Emitting Diode

75 1907(!) The first electroluminescent diode - SiC, H.J. Round (c) (Rediscovered by Losevem at 1928) Destriau - LEDs from ZnS Welker introduction of A III B V (GaAs) Lasers (RCA, GE, IBM, MIT) th- Expansion of epitaxial technologies th Implementation of heterostructures and quantum wells Solving of the laser degradation and diodes (dislocation free substrates).

76 LD Laser Diode and Semiconductor lasers it is nearly the same, but not quite (there are also semiconductor lasers without P-N junction pumped by light).

77 Laser jako prvek se zpětnou vazbou. Pásová struktura jednoduchý p-n přechod, injekce elektronů. Laserový čip hetrorostruktura, vlnovod, rezonátor. Vlnovod.

78 Resume LED relatively cheap, efficient, notdegrading light sources Further increasing of efficiency (to 90%) and power (up 10 W per chip). Cheap white colour, (tuneability of the colour temperature from blue to yellow); fundamental energy savings. Wavelength expansion to UV and MIR. Multicolour chips for white colour. LD versus classical lasers = analogy vacuum electronics versus transistors? Wavelength expansion to UV and MIR (we are engaged in it),... Further increasing of efficiency (more than 90%) and power (over 20W per chip). Multicolour chip; parallel optical communication. Controlling of colour; laser spectroscopy. One photon sources for quantum communications,... ; Lifetime, cost,