Kapitoly z nanoelektroniky Nanoelectronic Chapters (koordinuje prof. E. Hulicius, FZÚ AV ČR, v.v.i.)

Transkript

1 Přednášky pro TU v Liberci Studijní program:nanotechnologie Nanomateriály Studijní obor: (organizuje prof. J. Šedlbauer, FPP TU v Liberci) Kapitoly z nanoelektroniky Nanoelectronic Chapters (koordinuje prof. E. Hulicius, FZÚ AV ČR, v.v.i.) Čtyřhodinové bloky. Letní semestr 2014/2015 (to jest od února 2015 do června 2015). Zkouška (hlavně podle kvality a prezentace semestrální práce a případně podle znalostí převážně z oboru přiléhajícího k práci).

2 Semestrální práce: Přednášející vypíší témata ze svého oboru, ze kterých si studenti vyberou a zpracují je pod dohledem dotyčného přednašeče formou seminární práce (5-15 str.) a přednesou svým kolegům během jedné či dvou posledních čtyřhodinovek a za to obdrží známku. Mělo by jít o aktuální "state of art" daného tématu (které by mělo jistým způsobem doplňovat příslušnou přednášku), zpracovaného tak, aby srozumitelně poskytl svým kolegům novou a zajímavou informaci. Témata prací jsou na konci sylabů této přednášky. Téma je možné domluvit si individuálně s přednášejícím podle zájmu. Zkouška předmětu Kapitoly z nanoelektroniky spočívá hlavně ve vypracování a přednesení a obhájení seminární práce a případně ještě v zodpovězení otázek z bloku, ze kterého je tato seminární práce (pochybnosti učitele o známce, student ji chce lepší,...).

3 Příklady témat semestrálních prací z Vybraných kapitol z nanomateriálů 2015 Blok E. Huliciuse (hulicius@fzu.cz) (a badatelů z Fyzikálního ústavu AV ČR, Praha 6, Cukrovarnická 10; je: jmeno.přímení@fzu.cz Aliaksei Vetushka: 1) Netradiční formy křemíku, zajímavé pro nanoelektroniku. Jiří J. Mareš a Pavel Hubík 2) Nekonvenční supravodivost ve vrstvách nanokrystalického diamantu. Eduard Hulicius: 3) Kvantové tečky v polovodičových laserech. 4) Termofotovoltaika - princip, aplikace. Sronání s fotovoltaikou. 5) Jaké jsou na českém trhu LEDky barva, výkon, cena, další 6) Jaké jsou na českém trhu LD (laserové diody) barva, výkon, cena, další Alice Hospodková: 7) Polovodičové nitridové nanostruktury pro LED. 8) Polovodičové nitridové nanostruktury pro HEMT. Dušan Nohavica nohavica@ufe.cz : 9) Antibakteriální působeni nanočástic kladné a záporné efekty. 10) Ekotoxicita vliv na životní prostředí. Antonín Fejfar + Martin Ledinský: 11) Nanostrukturované sluneční články. 12) Perovskitove vrstvy pro fotovoltaiku. Alexander Kromka: 13) Nanokrystalické diamantové tenké vrstvy pro biosensory a MEMS (micro electro mechanical systems). 14) Deposice vrstev a aplikační využiti nanodiamantů. Ivan Gregora: 15) Ramanova Spektroskopie pro nanomateriály. Stanislav Kamba: 16) Nanodielektrika. Jiří Oswald: 17) Ramanova a luminiscenční mikrospektroskopie nitridových nanostruktur. A kdo chce, může oslovit libovolného zajímavého přednašeče a domluvit se s ním. Kontaktní osoba poskytne podklady, konzultace a přečte elaborát. Každé téma lze případně rozvést do diplomové, v některých případech i do disertační (doktorské) práce.

4 Chapters on nanoelectronics E. Hulicius, FZÚ AV ČR, v.v.i.

5 Technology of nanostructure preparation, nano-heterostructures A III B V (quantum dots and wells) preparation, properties, applications E. Hulicius, FZÚ AV ČR, v. v. i. (hulicius@fzu.cz) 0. What does it means nano. Are current definitions correct? 1. Epitaxial growth of layers and structures - Principles, phases and types of growth. Sorts of epitaxy epitaxy from solid, liquid and gas phases. Epitaxial growth from the material point of view. 2. Epitaxial techniques for semiconductor nanostructures preparation The fundamental methods are Epiataxy from molecular beams (Molecular Beam Epitaxy - MBE) and gas epitaxy from organometalic compounds (MetalOrganic Vapour Phase Epitaxy - MOVPE). Detail descriptions of both techniques, comparison, differences, limits, fields of application, parameters of chosen structures. Growth of QW, QWr, QD and quantum cascade structures. Short history of both technologies development.

6 Technology of nanostructure preparation, nano-heterostructures A III B V (quantum dots and wells) preparation, properties, applications 3. Characterisation "in situ" techniques - Description of the electron, optical, structural methods. Implementation of these methods during epitaxial growth. Their limits due to using during growth in situ. Possible recommended literature (available at the lecturer): V.A. Schuskin, N.N. Ledentsov, D. Bimberg, Epitaxy of Nanostructures, Springer- Verlag, Berlin Heidelberg New York 2004, ISBN M.A. Herman, W. Richter, H. Sitter, Epitaxy, Springer-Verlag, Berlin Heidelberg New York 2004, ISBN Guozhong Gao, Nanostructures and Nanomaterials, Imperial College Press, London 2004, ISBN V.M. Ustinov, A.E. Zhukov, A.Y. Egorov, N.A. Maleev, Quantum dot lasers, Oxford University Press, 2003, ISBN

7 In general: NANO is not only because it is small! Quantum effect starts to be fundamental.

8

9

10 Well known Moor law (about exponential decreasing of size of electronic devices and subsequent increasing of memory and speed), its history and potential future scenarios. Context with NANO. Quantum effects.

11

12 Paradigma of the quantum dots Moving from atomic electron levels over electron (hole) energy band structures to again discrete electron (hole) energy levels. Fundamental role of NANO. Quantum effects.

13 Atom - Solid state - Quantum dot

14 Procedures: Bottom-up a Top-down and also something between Examples of preparation or creations of the nanostructures Top-down cutting Bottom-up building something between self made self-assembled

15

16 Nanostructure preparation can be very simple...

17

18 or very complicated, difficult and expensive:

19

20 EPITAXIAL TECHNOLOGY in general Eduard Hulicius Laboratoř MOVPE, Oddělení polovodičů, Fyzikální ústav AV ČR Praha 6, Cukrovarnická Web FZÚ AV ČR, v.v.i. Brána pro veřejnost

21 Epitaxial technology Name epitaxe origins from Greek epi-taxis which means arranged on" was introduced by L. Royer at It is monocrystalic growth on (usually) monocrystalic substrate (wafer). Growth is not (usually) epitaxial when lattice constant difference is bigger than 15%. Explanation of importance and principles and comparison with other monocrystal preparation methods Why so monstrous, expensive, danger and demanding technology equipments Preparation and properties of the bulk crystals. Epitaxial growth advantages, new possibilities, limits. Homo- and heteroepitaxy. Equation of minimum of energy. Principle of the epitaxial growth. Atoms or molecules of the compound, which we would like to deposit on suitable substrate, are transported to its surface, which have to be atomically clean cleaned from oxides and sorbants - and atomically smooth (only with atomic steps due to disorientation of the monocrystalic substrate). On the surface the atoms will be physysorbed, and after that chemisorbed to the crystal structure. By this way atomic layers and all structure are grown.

22 Preparation and properties of the bulk crystals:

23 Preparation and properties of the bulk crystals:

24 Growth of monocrystals by the Czochralsky method

25 Bulk monocrystals, have impresive parametres - (atomic periodicity of monocrystal lattice more than one meter!), but they are not crystalographicly perfect nad for majority of electronic, namely optoelectronic, applications are not suitable. The reason is high temperature during their creation from melted material. We have to prepare materials and structures using epitaxial technologies which work at lower temperatures.

26 Epitaxy technologies Name epitaxe origins from Greek epi-taxis which means arranged on" was introduced by L. Royer at It is monocrystalic growth on (usually) monocrystalic substrate (wafer). Growth is not (usually) epitaxial when lattice constant difference is bigger than 15%. Explanation of importance and principles and comparison with other monocrystal preparation methods Why so monstrous, expensive, danger and demanding technology equipments Preparation and properties of the bulk crystals. Epitaxial growth advantages, new possibilities, limits. Homo- and heteroepitaxy. Equation of minimum of energy. Principle of the epitaxial growth. Atoms or molecules of the compound, which we would like to deposit on suitable substrate, are transported to its surface, which have to be atomically clean cleaned from oxides and sorbants - and atomically smooth (only with atomic steps due to disorientation of the monocrystalic substrate). On the surface the atoms will be physysorbed, and after that chemisorbed to the crystal structure. By this way atomic layers and all structure are grown.

27 Epitaxy technologies Epitaxial growth of monocrystalic layers (on the bulk monocrystal wafers = substrates) is realised at lower temperature than growth of monocrystals from melted material, which is substantial for: Influence of the enthropy (native defects), lower solutibility of the unintentional impurities into the prepared layers. Nevertheless this lower temperature (usually around 500 C) is high enough for creation of atomically clean and flat surface and enable atoms jump over the energy barriers for physisorption and chemisorption.

28

29 Solid State Epitaxy - SPE The old method with new applications. Metastable amorphous phase of solid state material, which is in touch with monocrystal, gradually assume crystalline form starting from the junction, copy monocrystal lattice, but with much lower point defect concentration. Growth speed usually nm per second is controlled by activation energy SPE E a : v = v 0 exp (-E a /kt) Applications: Preparation of thick semiconductor epitaxial layers with high doping. Low temperature epitaxy (Ga(Mn)As spinotronics?). Growth of the buffer layers for improving of properties of heterostructures decreasing dislocation densities - Nitrides! Silicide layers for electric contacts and Schottky barriers for Si devices.

30 Steps of the Solid State Epitay:

31

32 Liquid Phase Epitaxy - LPE The most important epitaxial method during seventies and eighties of the last century. Still using in the industry (cheap LEDs and when tens of micrones are necessary). Important for thermodynamical equilibrium grown structures. Princip of the LPE: Saturated solution of suitable materials (e.g. As in Ga) is cooling (or the liquid part is evaporated this is not realistic for Ga (it has low vapour pessure)) and thus starts to be oversaturated, thus As is going out from solution and created GaAs on the reasonable bulk or epitaxial substrate.

33

34 Vapour phase Epitaxy - VPE Todayand at least next ten years it will be the most important semiconductor preparation technology not only for industry but also for research. In principle it is possible to describe it as physical (PVD - Physical Vapour Deposition) and chemical (CVD - Chemical Vapour Deposition), according the transport of material from the source to the substrate. At first PVD it is evaporation of atoms or molecules (using heat, sputtering, ablation, discharge, etc.) without their chemical changes. At second CVD it is transport of volatile chemical compounds (precursors) using some transport gases (H2, N2) to the heated substrate near of its surface their are decomposed. Epitaxial growth on atomically clean and flat surface of usually monocrystalical substrate (wafer) is then similar. Also parameters of prepared layers are similar. In both cases we need extreme semiconductor cleanness vacuum (10-10 torr) or transport gas H 2 či N 2 (at the level of fractions of ppb).

35 Examples: Halide epitaxy Metals or elementary semiconductors - (WF 6 W +..., SiCl 4 Si +...) Compound semiconductors - (GaCl + AsH 3 GaAs +...) Granits of rare earths - (YCl 3 + FeCl 2 + O 2 Y 3 Fe 5 O ) Oxide epitaxy Compound semiconductors - (GaO 2 + PH 4 GaP +...) Hydride epitaxy Elementary semiconductors, very important silicon - (SiH 4 Si +...) Izolating layers: oxides, nitrides - (SiH 4 + H 2 O SiO ; SiH 4 + NH 3 Si 3 N ) Organometalic epitaxy Compound semiconductors - (Ga(CH 3 ) 3 + AsH 3 GaAs +...) Metals - (Al(C 4 H 9 ) 3 Al +...) High-temperature supraconductors YBaCuO

36 Main types of VPE growths Molecular epitaxy - MBE (Molecular beam epitaxy) SSMBE = SolidSource MBE, CBE = ChemicalBeamEpitaxy, GSMBE = GasSource MBE (HydrideSource MOMBE, MetalOrganic MBE), UHV ALE = UltraHighVacuum AtomicLayerEpitaxy Vapour epitaxy from organometalic compounds - MOVPE (MetalOrganic Vapour Phase Epitaxy) MOCVD (MetalOrganic Chemical Vapour Deposition) Photo-MOVPE (Nonthermal, light activated) Plasma-MOVPE (Nonthermal, plasma activated)

37 The most important for nanotechnology are MBE and MOVPE Molecular beam epitaxy - MBE We can sort it according the sources o the molecular beams: Solid Source MBE, Gas Source MBE (or Chemical Beam Epitaxy) Hydride Source MBE, MetalOrganic MBE, Schema and photos of different equipments produced by some producers:

38 Zdroj:

39

40

41

42 Molecular beam epitaxy Principle of method: Substrate(s) is heated in the high vacuum (10 -(9-10) torr) up to so high temperature when native oxides and surface impurities are desorbed and surface of the substrate is atomically clean. Then preheated Knudsen (effusion) cell will be open and atoms or molecules fly several tens centimetres without collisions through growth chamber on the substrate (they are also evaporated at the vicinity of substrate). Atoms of future epitaxial layer sit on the surface (physisorption) moving to the proper crystallographic sites where they are bounded (chemisorption). By this way the epitaxil layer is created. Substrate is monocrystallic semiconductor wafer with diameter from 2 to 8 inches, which is μm thick. Questions?

43 Expected questions: Why this substrate size? How input and také out substrate? What is maximal size of substrate(s)? Substrate(s) is heated in the high vacuum (10-(9-10) torr) up to so high temperature when native oxides and surface impurities are desorbed and surface of the substrate is atomically clean. Then preheated Knudsen (effusion) cell will be open and atoms or molecules fly several tens centimetres without collisions through growth chamber on the substrate (they are also evaporated at the vicinity of substrate). Atoms of future epitaxial layer sit on the surface (physisorption) moving to the proper crystallographic sites where they are bounded (chemisorption). By this way the epitaxil layer is created. Substrate is monocrystallic semiconductor wafer with diameter from 2 to 8 inches, which is μm thick.

44 Expected questions: Why this substrate size? How input and také out substrate? What is maximal size of substrate(s)? Why substrate rotates? Substrate(s) is heated in the high vacuum (10-(9-10) torr) up to so high temperature when native oxides and surface impurities are desorbed and surface of the substrate is atomically clean. Then preheated Knudsen (effusion) cell will be open and atoms or molecules fly several tens centimetres without collisions through growth chamber on the substrate (they are also evaporated at the vicinity of substrate). Atoms of future epitaxial layer sit on the surface (physisorption) moving to the proper crystallographic sites where they are bounded (chemisorption). By this way the epitaxil layer is created. Substrate is monocrystallic semiconductor wafer with diameter from 2 to 8 inches, which is μm thick.

45 Expected questions: Why this substrate size? How input and také out substrate? What is maximal size of substrate(s)? Why substrate rotates? Why so high vacuum is necessary? Substrate(s) is heated in the high vacuum (10-(9-10) torr) up to so high temperature when native oxides and surface impurities are desorbed and surface of the substrate is atomically clean. Then preheated Knudsen (effusion) cell will be open and atoms or molecules fly several tens centimetres without collisions through growth chamber on the substrate (they are also evaporated at the vicinity of substrate). Atoms of future epitaxial layer sit on the surface (physisorption) moving to the proper crystallographic sites where they are bounded (chemisorption). By this way the epitaxil layer is created. Substrate is monocrystallic semiconductor wafer with diameter from 2 to 8 inches, which is μm thick.

46 Expected questions: Why tihis substrate size? How input and také out substrate? What is maximal size of substrate(s)? Why substrate rotates? Why so high vacuum is necesary? How open and close effusion cells? Influence on vacuum? Substrate(s) is heated in the high vacuum (10-(9-10) torr) up to so high temperature when native oxides and surface impurities are desorbed and surface of the substrate is atomically clean. Then preheated Knudsen (effusion) cell will be open and atoms or molecules fly several tens centimetres without collisions through growth chamber on the substrate (they are also evaporated at the vicinity of substrate). Atoms of future epitaxial layer sit on the surface (physisorption) moving to the proper crystallographic sites where they are bounded (chemisorption). By this way the epitaxil layer is created. Substrate is monocrystallic semiconductor wafer with diameter from 2 to 8 inches, which is μm thick.

47 Expected questions: Why this substrate size? How input and take out substrate? What is maximal size of substrate(s)? Why substrate rotates? Why so high vacuum is necessary? How high substrate temperature is necessary? How recharge, heat, open and close effusion cells? Influence on vacuum? Substrate(s) is heated in the high vacuum (10-(9-10) torr) up to so high temperature when native oxides and surface impurities are desorbed and surface of the substrate is atomically clean. Then preheated Knudsen (effusion) cell will be open and atoms or molecules fly several tens centimetres without collisions through growth chamber on the substrate (they are also evaporated at the vicinity of substrate). Atoms of future epitaxial layer sit on the surface (physisorption) moving to the proper crystallographic sites where they are bounded (chemisorption). By this way the epitaxil layer is created

48 Expected questions: Why this substrate size? How input and take out substrate? What is maximal size of substrate(s)? Why substrate rotates? Why so high vacuum is necessary? How high substrate temperature is necessary? How recharge, heat, open and close effusion cells? Influence on vacuum? Are there difference between atomic and molecular beam? Substrate(s) is heated in the high vacuum (10-(9-10) torr) up to so high temperature when native oxides and surface impurities are desorbed and surface of the substrate is atomically clean. Then preheated Knudsen (effusion) cell will be open and atoms or molecules fly several tens centimetres without collisions through growth chamber on the substrate (they are also evaporated at the vicinity of substrate).

49 Expected questions: Why this substrate size? How input and take out substrate? What is maximal size of substrate(s)? Why substrate rotates? Why so high vacuum is necessary? How high substrate temperature is necessary? How recharge, heat, open and close effusion cells? Influence on vacuum? Are there difference between atomic and molecular beam? How is MBE influence by growth chamber size? Substrate(s) is heated in the high vacuum (10-(9-10) torr) up to so high temperature when native oxides and surface impurities are desorbed and surface of the substrate is atomically clean. Then preheated Knudsen (effusion) cell will be open and atoms or molecules fly several tens centimetres without collisions through growth chamber on the substrate (they are also evaporated at the vicinity of substrate).

50 Expected questions: Why this substrate size? How input and take out substrate? What is maximal size of substrate(s)? Why substrate rotates? Why so high vacuum is necessary? How high substrate temperature is necessary? How recharge, heat, open and close effusion cells? Influence on vacuum? Are there difference between atomic and molecular beam? How is MBE influence by growth chamber size? What influenced growth speed? Substrate(s) is heated in the high vacuum (10-(9-10) torr) up to so high temperature when native oxides and surface impurities are desorbed and surface of the substrate is atomically clean. Then preheated Knudsen (effusion) cell will be open and atoms or molecules fly several tens centimetres without collisions through growth chamber on the substrate (they are also evaporated at the vicinity of substrate).

51 Expected questions: Why this substrate size? How input and take out substrate? What is maximal size of substrate(s)? Why substrate rotates? Why so high vacuum is necessary? How high substrate temperature is necessary? How recharge, heat, open and close effusion cells? Influence on vacuum? Are there difference between atomic and molecular beam? How is MBE influence by growth chamber size? What influenced growth speed? Why epitaxial layer is only on the substrate?

52 Expected questions: Why this substrate size? How input and take out substrate? What is maximal size of substrate(s)? Why substrate rotates? Why so high vacuum is necessary? How high substrate temperature is necessary? How recharge, heat, open and close effusion cells? Influence on vacuum? Are there difference between atomic and molecular beam? How is MBE influence by growth chamber size? What influenced growth speed? Why epitaxial layer is only on the substrate? How stop the growth?

53 Expected questions: Why this substrate size? How input and take out substrate? What is maximal size of substrate(s)? Why substrate rotates? Why so high vacuum is necessary? How high substrate temperature is necessary? How recharge, heat, open and close effusion cells? Influence on vacuum? Are there difference between atomic and molecular beam? How is MBE influence by growth chamber size? What influenced growth speed? Why epitaxial layer is only on the substrate? How stop the growth? Financial tasks? Cost of one growth, structure, chip, equipment?

54 Expected questions: Why this substrate size? How input and take out substrate? What is maximal size of substrate(s)? Why substrate rotates? Why so high vacuum is necessary? How high substrate temperature is necessary? How recharge, heat, open and close effusion cells? Influence on vacuum? Are there difference between atomic and molecular beam? How is MBE influence by growth chamber size? What influenced growth speed? Why epitaxial layer is only on the substrate? How stop the growth? Financial tasks? Cost of one growth, structure, chip, equipment? Main troubles of growths?

55 Expected questions: Why this substrate size? How input and take out substrate? What is maximal size of substrate(s)? Why substrate rotates? Why so high vacuum is necessary? How high substrate temperature is necessary? How recharge, heat, open and close effusion cells? Influence on vacuum? Are there difference between atomic and molecular beam? How is MBE influence by growing chamber size? What influenced growth speed? Why epitaxial layer is only on the substrate? How stop the growth? Financial tasks? Cost of one growth, structure, chip, equipment? Main troubles of growths? In-situ diagnostics?

56 The most important for nanotechnology are MBE and MOVPE Molecular beam epitaxy - MBE MBE is vacuum (exactly highvacuum ) method, so we can use majority of the electron characterisation techniques. Scheme of in-situ measuring technique RHEED, picture on the screen is created by electron reflected by the crystal surface. Dependence of signal on the growth time is shown. Size of electrons (probability of their position in the space = de Broglieho wavelength) is comparable with the crystal (= with size of atoms).

57 Zdroj:

58 The most important for nanotechnology are MBE and MOVPE: Organometalic Vapour Phase Epitaxy MOVPE (MetalOrganic Vapour Phase Epitaxy) This technology is not so controllable and exact for research as MBE, (which has better control of growth driving, it is able to prepare sharper hetero-boundaries and lower growth temperatures), but it is fundamental for industry, mainly for optoelectronic devices. MOVPE is cheaper, with higher productivity and it is more suitable for nitrides.

59 Organometalic Vapour Phase Epitaxy - MOVPE The most important industrial and very importatnt research technology Principle of method: Substrate(s) is heated in the ultra clean gas (hydrogen, nitrogen) up to so high temperature when native oxides and surface impurities are desorbed and surface of the substrate is atomically clean. Then we will send to the quartz reactor suitable precursors (organometals, hydrides) they will be thermally decomposed at the vicinity of preheated substrate. Atoms of future epitaxial layer sit on the surface (physisorption) moving to the proper crystallographic sites where they are bounded (chemisorption). By this way the epitaxial layer is created. Qestions?? Basic summary equation for GaAs growth from trimethylgallium (TMGa) and arsine Ga(CH 3 ) 3 + AsH 3 GaAs + 3CH 4 and similar for ternary semiconductor compounds xga(ch 3 ) 3 + (1-x)Al(CH 3 ) 3 + AsH 3 Ga x Al (1-x) As + 3CH 4

60 Examples of organometalic molecules:

61

62 Equiations for growth of GaAs are not so simple:

63 2Ga(CH 3 ) 3 3CH 3 + Ga(CH 3 ) 2 + Ga(CH 3 ) CH 3 + AsH 3 AsH 2 + CH 4 Ga(CH 3 ) + AsH 2 GaAs + CH 4 + H

64 Detail description is more komplex (Stringfellow):

65

66 Organometalic Vapour Phase Epitaxy - MOVPE Brief History: Ruhrwein US patent (1968) Manasevit first experiments (1968) Hall, Stringfellow importatnt developement of method Dupois, Dapkus clean organometals (1977/78) The most important industrial semiconductor technology ( )

67 Photo of equipment Schema Examples of organometalic molecules Bubler botle for organometals

68 Zdroj:

69 Epitaxial specialities Growth out of thermodynamical equilibrium: SPE and LPE no, MBE a MOVPE yes. It can be usefull for preparation of the strained layers. Lattice not-matched strained layers nanostructures OK, thicker layers relax dislocations are created no luminescence. Strained layers (nanostructures) can have new desired properties - change of material type (direct indirect semiconductor), - separation of light and heavy holes (fundamental increase of limit frequency), - moving of levels in quantum wells (laser wavelength tuning). Epitaxial transverse overgrowth (ELO Epitaxial Lateral Overgrowth) Very successful for nitride growth! (blue LEDs, lasers,...)

70 For MOVPE is not able to use electron diagnostic techniques (the growth is running close to atmospheric preasure of hydrogen or nitrogen). Photons are much bigger than crystal lattice constant, but when the light is polarised and can interag with larger part of surface which is changed during the growth, we can use them. RAS and its explanation:

71 In situ growth monitoring and controling I In situ monitoring RAS (Reflection Anisotropy Spectroscopy) allows to monitor and control processes taking part during the epitaxial growth, such as the formation of QDs during the InAs deposition and during the waiting time or the 3D object dissolution during the QD overgrowth. It is therefore easier to optimise the amount of deposited InAs and the waiting time or even other technological parameters (V/III ratio, growth temperature, growth rate, SRL composition). Using these data it is possible to control parameters of the prepared structures through the technological parameters during the growth.

72 In situ growth monitoring and controling II In situ monitoring RAS (Reflection Anisotropy Spectroscopy) Linearly polarised light is shone on a sample under perpendicular incidence. The elliptically polarised reflected light runs through a photoelastic modulator and a second polarising prism. The modulated intensity is analysed by a monochromator and a detector

73 In situ growth monitoring and controling III Quantum dot growth

74 In situ growth monitoring and controling I In situ monitoring RAS (Reflection Anisotropy Spectroscopy) Types of imagine. Spectroscopic Colorplot Time resolved

75 Exact and full complex understanding of the epitaxial growths needs quantum mechanical approach. This is rather difficult. Thank you for your attention

76 Questions and answers Heterostructures: Semiconductor heterostructures in some of devices (you can choose one)? New effects tunnel diode, quantum cascade laser, Ohm normal (quantum Hall effect),... Fundamental improvement of parameters LD (CW at room temperature), LED (high efficiency, colours), planar waveguides,...localisation of electrons and holes and light,... Technology in general: Name three main reasons for using of epitaxial technologies! It is possible to prepare material of better quality than from melted material the lower temperature the lower entropy and the lower solubility of undesired impurities. Higher reproducibility of the heterostructure preparation more controlled structure= better devices Possibility of nanostructure preparation new effects. Possibility of separation of photons and electrons in the device structure LD, LED. Possibility of separation of electrons and their donors high mobility = HF devices. In-situ Nanocharacterization a diagnostics: Describe difference between RAS a RHEED! RAS = Reflectance Anisotropy Spectroscopy, is optical non vacuum method, which is suitable despite much bigger size of photons than lattice constant. It is working because of full surface atom arrangement during different stages of layer or structure growth and polarized photons can see surface arrangement of atoms. RAS can monitor growth of individual monolayers via ML oscillation. It can give information about QD and QW growth. But it has lower resolution than vacuum RHEED. RHEED = electron vacuum method of the surface study, it cam work only in the ultrahigh vacuum, there are possibility of surface study by electron methods, possibility of monitoring of growth of individual monolayers via ML oscillation. It is possible to prepare sharp and define heterojunctions layer thickness is controlled with accuracy of fractions of ML, because the electron size (= de Broglie wavelength space of probability of electron location) is comparable with crystal lattice constant.

77 Otázky a odpovědi - průběžné Heterostruktury: Jaký je rozdíl mezi klasickou polovodičovou heterostrukturou a nano(hetero)strukturou? Klasická heterostruktura přináší podstatné zlepšení parametrů LD (CW při pokojové teplotě), LED (vysoká účinnost), planární vlnovody,...lokalizace nosičů náboje a světelného pole,..., ale materiál zůstává bulk-like. Nanostruktura přináší nové jevy tunelová dioda, kaskádové lasery, normál ohmu (kvantový Hallův jev),.., neboť se začínají projevovat kvantové jevy. Technologie obecně: Proč je MOVPE vhodnější pro průmysl než MBE uveďte alespoň tři důvody. Větší plochy substrátů, lepší homogenita, kontinuální možnost výměny prekursorů, větší materiálová diverzita,větší výtěžnost, In-situ Nanocharakterizace a diagnostika: Jsou možné i jiné in-situ metody než RAS a RHEED? 1) Jako je optické měření teploty, zakřivení struktury při růstu, homogenity složení: 2) Co úplně jiné metody jako je STM, epipsometrie, RTG záření a pod. 1) Ano s velkou výhodou, hlavně průmyslově: a) optické měření teploty na principu termovize b) zakřivení vzorku (struktury) při růstu odrazem laserového paprsku na různých místech od povrchu struktury dává informaci nejen o topologii, ale i o pnutí ve struktuře a může se srovnávat stejnost, což je pro průmyslové růsty velmi důležité. 2) Ano, ale velmi omezeně, hlavně pro výzkum.

78 Druhá část pro pokročilejší zájemce Kvantové jámy, tečky a podobné nanostruktury Detaily a vysvětlení najdete v citované literatuře.

79 Kvantové jámy Kvantování elektronových (děrových) energetických (energiových?) stavů ve vrstvě s příčným rozměrem srovnatelným s vlnovou délkou (pravděpodobností výskytu) elektronu, vytvořenou potenciálovými bariérami (příklad je polovodičová heterostruktura). Umíte?

80 Výhody QD Hustota stavů ve tvaru delta funkcí snížení nezářivé rekombinace (Auger a IVBA). Nižší prahová proudová hustota v laserech s KT. Lepší teplotní stabilita prahového proudu. Snížení nezářivé rekombinace na zrcadlech. KT umožňují emisi na vlnových délkách 1.3 m i 1.55 m také v systémech InAs/GaAs, tedy na GaAs substrátu.

81 InAs QD

82 Atom - Pevná látka - Kvantová tečka

83 Proč jsou QD tak intenzivně studovány? KJ KT Hustota stavů v objemovém polovodiči, kvantové jámě a kvantové tečce (E) 3D 2D 0D E 1 E 2 E 3 E 4 E

84 Hustoty stavů

85 Stranského-Krastanowův mód růstu Vysoce napnuté struktury: rozdíl v mřížkových konstantách kolem 7% InAs GaAs

86 Kvantová tečka v řezu

87 Naše výsledky

88 Growth and properties of InAs/In x Ga 1-x As/GaAs quantum dot structures E. Hulicius 1, J. Oswald 1, J. Pangrác 1, J. Vyskočil 1,3, A. Hospodková 1, K. Kuldová 1, K. Melichar 1, T. Šimeček 1, T. Mates 1, V. Křápek 4, J.Humlíček 4, J. Walachová 2, J. Vaniš 2, P. Hazdra 3, and M. Atef 3 MOVPE laboratory 1 Institute of Physics AS CR, v. v. i., Cukrovarnická 10, , Prague 6, Czech Republic 2 Institute of Photonics and Electronics AS CR, v. v. i., Chaberská 57, Prague 8, Czech Republic 3 CTU - FEE, Technická 2, , Prague 6, Czech Republic 4 MU - PřF, Kotlářská 2, Brno, Czech Republic

89 Possible solutions, access and approaches To increase QD size quantum levels in QDs will be lower (electron and hole levels are more closely). To change strain inside QDs. But it is necessary to keep distance between QD ground state and excited states high enough (for better laser emission). Types of structures: Vertically correlated; with Strain reducing layer; Elongated QDs. In-situ measurement: Reflectance anisotropy spectroscopy. Ex-situ direct measurement: ballistic electron emission microscopy and spectroscopy, Photomodulated Reflectance, (Magneto)Photoluminescence. Modeling and Simulations.

90 Vertically correlated structures Lateral shape of InAs/GaAs quantum dots in vertically correlated structures We found ways to control the energy difference between PL transitions by adjusting properly the spacer thickness, the number of QD layers, and the growth conditions (e.g. V/III ratio). We also found an efficient way to control the emission wavelength by changing the number of QD layers. A. Hospodková, E. Hulicius. J. Oswald, J. Pangrác, T. Mates, K. Kuldová, K. Melichar, and T. Šimeček, Properties of MOVPE InAs/GaAs quantum dots overgrown by InGaAs, J. Cryst. Growth, 298 (2007),

91 Spacer thickness Vertically correlated structures 1.8 QD elongation a/b circular QD [-110] b [110] a Blue = InAs Yellow = GaAs Spacer thickness [nm] Energy difference [mev] 70 E PL intensity [a.u.] Energy [ev] Spacer thickness [nm] J. Cryst. Growth 298 (2007)

92 Magnetophotoluminescence, elongation Elongation of InAs/GaAs QD determined from magnetophotoluminescence measurements We use magnetophotoluminescence for determination of the lateral anisotropy of buried quantum dots. While the calculated shifts of the energies of higher radiative transitions in magnetic field are found to be sensitive to the lateral elongation, the shift of the lowest transition is determined mainly by the exciton effective mass. This behavior can be used for determining both the effective mass and the elongation fairly reliably from spectra displaying at least two resolved bands. V. Křápek, K. Kuldová, J. Oswald, A. Hospodková, E. Hulicius, J. Humlíček, Elongation of InAs/GaAs quantum dots from magnetophotoluminescence measurements, Appl. Phys. Lett. 89 (2006)

93 Magnetophotoluminescence, elongation Fig. 1 MPL energies calculated for a) circular and b), c) elongated QDs. Parameters used in the calculations: m* = 0:045m 0, ħ x = 100 mev, a) ħ y = 100meV (L = 1:0), b) ħ y = 150meV (L = 1:5), c) ħ y = 200meV (L = 2:0). The energies of the lowest transition at zero field were set to 1.1 ev (corresponding to the vertical confinement energy). Appl. Phys. Lett. 89 (2006)

94 Magnetophotoluminescence, elongation Fig. 2 Energy of the lowest MPL transition against magnetic field for elongated QDs. The experimental values (squares) and calculated energies with parameters ħ x = 100 mev, ħ y going from 100meV (thinner lines) to 200meV (thicker lines), and effective masses 0:03m 0 (dashed), 0.04m 0 (dotted), 0.05m 0 (dash dotted), 0.06m 0 (dash dot dotted), indicated by the arrows. The best agreement with the experimental data has been obtained for ħ y = 160meV and m* = 0.045m 0 (thick solid line). Appl. Phys. Lett. 89 (2006),

95 Magnetophotoluminescence, elongation Fig. 3 Energy of the first higher MPL transition against magnetic field for elongated QDs. The experimental values (squares) and calculated energies with parameters ħ x = 100 mev, m* going from 0.045m 0 (thinner lines) to 0.05m 0 (thicker lines), and ħ y values of 100meV (dashed), 120meV (dotted), 140meV (dash dotted), 160meV (dash dot dotted), 180meV (short dashed), 200meV (short dotted). The best agreement with the experimental data has been obtained for ħ y = 160meV and m* = 0.045m 0 (thick solid line). Appl. Phys. Lett. 89 (2006),

96 Study of InAs quantum dots in AlGaAs/GaAs heterostructure by ballistic electron emission microscopy/spectroscopy BEEM / BEES J. Walachová, J. Zelinka, V. Malina, J. Vaniš, F. Šroubek, J. Pangrác, K. Melichar, and E. Hulicius, Study of InAs quantum dots in AlGaAs/GaAs heterostructure by ballistic electron emission microscopy/spectroscopy, Appl. Phys. Lett. 91 (2007) and Appl. Phys. Lett (2008) (different QD sizes)

97 BEEM (microscopy) AFM topography ballistic current (in pa at Itun = 2.5 na, V tun = 1.5 V)

98 BEES (spectroscopy), derivated from V-A characteristics of QD structure Appl. Phys. Lett. 91 (2007)

99 TEM AFM 7 vrstev KT, oddělovací vrstvy 7.5 nm 3 vrstvy KT, oddělovací vrstvy 3.7 nm

100 AFM obr. kvantových teček, pohled shora, několik vrstev

101 Technologie přípravy: MOVPE 7. GaAs krycí vrstva 6. GaAs oddělovací vrstva 5. Přerušení růstu 30 s 4. InAs napnutá vtstva (1.4 ML) 3. GaAs podklad. vrstva 500 o C 2. GaAs podklad. vrstva 650 o C 1. GaAs substrát GaAs vrstvy: Prekursory TMGa a AsH 3, celk. tlak 70 hpa, celk. průtok 8 l/min, teplota 650 o C a 500 o C, poměr V/III 150 a 43. InAs vrstvy: 50 ml/min H 2 /TMIn, poměr V/III 85, čas růstu 9 s, přerušení růstu 30 s.

102 QD překryté InGaAs Původní QD QD překrytá GaAs QD překrytá InGaAs

103 Dosažená vlnová délka FL InAs/InGaAs QD

104 FL InAs/GaAs QD překrytých InGaAs I PL (arb.u.) E PL (ev) 1508B bez ternaru 1524B 13%In I* B 23%In 1526B 6%In I*35 InGaAs 23% In InAs GaAs Základní stav: 0.86 ev 1.44 m 1. excitovaný stav: 0.93 ev 1.3 m

105 2 QD Samples SL thickness [nm] scheme Without GaAs capping layer (for AFM) A1 A2 A3 A4 A5 A6 With GaAs capping layer (for PL) Ac1 Ac2 Ac3 Ac4 Ac5 Ac6 PL: Pumped by semiconductor laser (808 or 980 nm line), Ge detector, standard lock-in technique. AFM: Veeco Dimension 3100, tapping mode, tip radius 10 nm.

106 Relation between GaAs SL thickness and QD lateral shape in VCQDs QD lateral ratio a/b 1.8 A circular 1.0 A2 0.8 A1 [-110] b [110] a Spacer thickness [nm] AFM, 500 x 500 nm : A1 [-110] A2 [-110] A4 [-110]

107 Reason of the lateral QD elongation The growth rate of GaAs in the [110] direction is strongly dependent on AsH 3, partial pressure, [1], [2]. Growth rate [ m/hour] lateraral growth [110] lateral growth [-110] vertical growth [001] AsH 3 partial pressure [1] G.B. Stringfellow: Organometalic Vapor-Phase Epitaxy: Theory and Practice, Academic Press, inc, San Diego, 1989; [2] H. Asai: Anisotropical lateral growth in GaAs MOCVD layers on (001) substrates, Journal of Crystal Growth 80 (1987).

108 Schema of the lateral QD elongation Smaller surface curvature Strain is less relaxed QDs are less elongated Greater surface curvature Higher elastic strain relaxation QDs are more elongated

109 Photoluminescence PL intensity [a.u.] x QD with capping layer Energy [ev] SL thickness: Ac1 2 nm Ac2 3.7 nm Ac3 5 nm Ac4 7.5 nm Ac5 10 nm Ac6 15 nm PL intensity [a.u.] x QD without capping layer A1 2 nm A2 3.7 nm A3 5 nm A4 7.5 nm A5 10 nm A6 15 nm Energy [ev] Maximum PL [ev] Maximum of PL [ev] on SL thickness 0,99 Ac4 A5 A6 0,98 Ac1 Ac5 0,97 A4 Ac6 0,96 0,95 0,94 Ac2 Ac3 0, SL thickness [nm] Energy difference E 1 [mev] Ac2 Ac3 PL intensity [a.u.] 6 E ,8 0,9 1,0 1,1 Emission energy [ev] Ac SL thickness [nm]

110 Kvantové jámy (QW) a mnohonásobné QW Heteropřechody druhého typu. Struktury s napnutými vrstvami. Kvantové tečky (QD).

111 Laserová struktura s dvanáctinásobnou kvantovou GaAs: buffer 230 nm jámou v aktivní oblasti AlGaAs-n typ 570 nm AlGaAs 400 nm GaAs 150 nm AlGaAs 320 nm AlGaAs-p typ 570 nm GaAs 700 nm GaAs:Te substrate SPSLS 12x (InAs / GaAs) STM Obr.

112 Srovnání laserů s ternární a supermřížkovou (nebo MQW) aktivní oblastí Ternární InGaAs QW laser InAs/GaAs laser se supermřížkou Optical Power [a.u.] Intensity EL I ex =2 A I ex =2.25 A I ex =2.5 A I ex =3 A T=300 K Emission Energy [ev] T 0 = 109 K Current Density [A/cm 2 ] laser A 25 o C 40 o C 50 o C 60 o C 70 o C 80 o C 85 o C Optical Power [ W] Intensity PL EL I ex =0.46A T=300K Emission Energy [ev] T 0 = 126 K Current Density [A/cm 2 ] laser B 25 C 35 C 45 C 55 C 65 C 75 C 85 C

113 Vlastnosti laserů s MQW v aktivní oblasti

114 Kvantové jámy (QW) Heteropřechody druhého typu Struktury s napnutými vrstvami Kvantové tečky (QD)

115 Heteropřechody: (a) = b - prvního typu (b) = a - druhého typu (c) - třetího typu D:\Storage\Eda\NSE\pr_1.jpg

116

117

118 Cizí výsledky

119 Příklady součástek, které jsou založeny na neklasických (neintuitivních) kvantových fyzikálních jevech Nebezpečná konkurence: Kaskádové lasery Obr 3 x Příklady a heterodimensionální struktury pro součástky Obr. + (3) Snad nejstarší příklad je tunelová dioda: Rezonanční tunelování. Obr. Tranzistory HEMT a další, například jednoelektronové tranzistory Obr. Kvantový etalon ohmu na základě kvantového Hallova jevu. Projekt MÚ, FEL a FZÚ (P. Svoboda) Polovodičové lasery, (ty s QW a QD dvojnásobně). Povídání o postupném i skokovém zlepšování parametrů se zaváděním nových struktur. Obr B 1.4.

120

121 Různé koncepce aktivní oblasti kaskádových laserů J.Faist, F.Capasso, C.Sirtori at al. (A.Y.Cho), a) 1994, b) 1998, c) 2001

122 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.

123 Příklady součástek, které jsou založeny na neklasických (neintuitivních) kvantových fyzikálních jevech Příklady a heterodimensionální struktury pro součástky Obr. + (3) Snad nejstarší příklad je tunelová dioda: Rezonanční tunelování. Obr. Tranzistory HEMT a další, například jednoelektronové tranzistory Obr. Kvantový etalon ohmu na základě kvantového Hallova jevu. Projekt MÚ, FEL a FZÚ (P. Svoboda) Polovodičové lasery, (ty s QW a QD dvojnásobně). Povídání o postupném i skokovém zlepšování parametrů se zaváděním nových struktur. Obr B 1.4.

124

125 Heterodimensional Device Technologies

126 Příklady součástek, které jsou založeny na neklasických (neintuitivních) kvantových fyzikálních jevech Snad nejstarší příklad je tunelová dioda. Rezonanční tunelování. Obr. Tranzistory HEMT a další, například jednoelektronové tranzistory Obr. Kvantový etalon ohmu na základě kvantového Hallova jevu. Projekt MÚ, FEL a FZÚ (P. Svoboda) Polovodičové lasery, (ty s QW a QD dvojnásobně). Povídání o postupném i skokovém zlepšování parametrů se zaváděním nových struktur.

127

128

129 Příklady součástek, které jsou založeny na neklasických (neintuitivních) kvantových fyzikálních jevech Tranzistory HEMT a další, například jednoelektronové tranzistory Obr. Kvantový etalon ohmu na základě kvantového Hallova jevu. Projekt MÚ, FEL a FZÚ (P. Svoboda) Polovodičové lasery, (ty s QW a QD dvojnásobně). Povídání o postupném i skokovém zlepšování parametrů se zaváděním nových struktur.

130

131

132 Příklady součástek, které jsou založeny na neklasických (neintuitivních) kvantových fyzikálních jevech Kvantový etalon ohmu na základě kvantového Hallova jevu. Projekt MÚ, FEL a FZÚ (P. Svoboda) Polovodičové lasery, (ty s QW a QD dvojnásobně). Povídání o postupném i skokovém zlepšování parametrů se zaváděním nových struktur.

133 Kvantový normál odporu

134 Kvantový normál odporu

135 Příklady součástek, které jsou založeny na neklasických (neintuitivních) kvantových fyzikálních jevech Polovodičové lasery a LEDky, (ty s QW a QD dvojnásobně). Povídání o postupném i skokovém zlepšování parametrů se zaváděním nových struktur. Obr B 1.4.

136 Děkuji za pozornost