RUSSIAN-ARMENIAN STATE UNIVERSITYPHYSICO-TECHNICAL DEPARTMENTOvsep Emin Str.123,Yerevan, ArmeniaProf. Stepan Petrosyanemail: firstname.lastname@example.orgDr. Vladimir Gevorkyan email: email@example.com
Growth and research of InAsSbP/InAs and Cu2O based heterostructures for photovoltaic and thermophotovoltaic applications Development of novel technological methods for the growth of III-V and ZnO nanowires for opto- and microelectronic device applications Theoretical and experimental study of high efficiency quantum dot solar cells Theory of nanoscale contacts and nanodevices (photodiodes, field-effect transistors, position-sensitive detector) Field of Scientific Activities
Novel diode heterostructures on the base of InAs alloys • Fields of applications Medical Diagnostics: glucose and other substances in blood, in tissue Water Sensors: water in paper, water in grain, water in oil products. Methane Sensors: for methane leakage in houses, along gas communications, in mines Medical Diagnostics: Carbon Dioxide, Acetone and gases in breath Mid IR Photodiodes Ecological monitoring of different industrial pollutants in air and water Systems of optical fibres communication Free-space optical link Energy production and energy-saving applications Thermophotovoltaic
ħ ω<Eg ħ ω<Eg Selective optical filter/reflector TPV cell (Eg) Heated body (emitter) 1000-2000ОС Source of thermal or solar energy Backside reflector Sources of solar and thermal energy for direct conversion to electricity on the base of TPV cells Engineering model of solar energy converter on the base of TPV cell • Thermophotovoltaic converters
Relative spectral response of the n+-InAs / n0-InAs / p+- InAs0.27Sb0.23P0.5 TPV diode heterostructure grown by non-equilibrium MOVPE growth technique Sl,max = 1.4 - 1.6 A/W h = 0.4 - 0.5 • Flexibility of the heat source, which includes solar and other thermal sources of energy • Compact in size • Light weight • Low Noise • TPV converters can provide 24 hours of electricity due to combining solar energy and thermal energy (combustion flame, etc.).
Band diagram of the n-InAs/p-InAs1-x-yPxSby TPV diode heterostructure EC Eg2 ħω EF EV Eg1 n-InAs Substrate p-InAs1-x-yPySbx emitter layer Sapphire Window Photo-diode Chip Amplifier • Mid-Infrared photodiodes Epitaxial filmready for Mid-IR device manufacturing Pilot model of Mid-IR Photodetector with parabolic reflector and amplifier as a final product. Maximum sensitivity without reflector ~1 nWatt. Packaged Mid-IR photo-diode. Schematic view and photo of an engineering model of infrared photo-diode.
Quantum Dot Solar Cell: Structure • Schematic diagram of QDSC • Corresponding energy band structure
Experimental results Theoretical results Quantum Dot Solar Cell: Results • Photocurrent density versus number of stacked layers compared with the photocurrent without QD’s. • Comparison of external quantum efficiency of the solar cells with different stacked layers and without dots
2D p-n JUNCTION • l ~ V • QW thickness dependent built-in potential • Small capacitance with log dependence on voltage • Very large breakdown voltage • High 2D electron mobility
VА=-4 eV (x) VA= 0 VА=4 eV z + + + 2ДЭГ - 2Д Металл + + + - + + - + - + + + + + + - l x + + + - - + + + - + + + + + + - + + + 2D Shchottky contact
x VG 2a + + + + + + + W(y) VS V(y) VD W(y) + + + + + + y L VG 2D electron gas field efect transistor 2DEG • High channel conductivity • Very high transconductance.
Laser Synthesis of the Colloidal Nanoparticles Laser ablation of materials in liquids Technique Applied: • Semiconductor Nanoparticles (Quantum Dots) • Metal Nanoparticles • Carbon Nanoparticles • Polymer Nanoparticles
Quantum Dots Blue-Ultraviolet Luminescence Ultrafine Sizes: 2-3nm
Ultrafine nano[particles in biological imaging • In a frog embryo has been imaged using • organic-dye techniques (b) Quantum Dots An important aspect of QD labels is their extremely high photostability, which allows monitoring of intra-cellular processes over long periods of time The capillary structure, is revealed with fluorescence microscopy as nanocrystal quantum dots circulate through the bloodstream.
Cancer Therapy&Diagnostics Specific labeling of live cells with Quantum Dots Breast cancer cells (A) and mouse mammary tumor tissue section (B) were stained with QDs
Magnetic Liquids • Magnetic nanoparticles with particle sizes small enough • to pass through the capillary systems of organs and tissues • Their movement in the blood can be controlled • with a magnetic field Nanostructures The ability to engineer nanoassemblies promise for a new generation of electronics, and optoelectronics Carbon Micro/Nanofibers Nanofibers • plasmonic subwavelength waveguiding • Plasmonic • optoelectronics
6 1 4, 5 3 2 Actually, as it follows from Fig. 1, NMR response precipitately changes upon the variation of the binder’s content. These data speak about the of the copper’s valence state increase from 2 to 2+Δ. Presumably, this is the underlying reason of Ts increase by 1 to 3 degrees. Fig.1. Cu2+(I) of the super conducting Y1Ba2Cu3O6.97 ceramics (curve 1); and composites with HMPE. Curve 2 – 1% ; Curve 3 – 3% ; Curve 4 – 5% ; Curve 5 – 10 % ; Curve 6 – 20 % .
Superconducting polymer-ceramic nanocomposites are obtained with various binders (superhighmolecular polyethylene, SHMPE; ramified polyethyelene, RPE; copolymerfluorine with polyethyelene, F-40; polyvinylidene fluoride, PVIF, etc.). From the data in table it follows that the critical transition temperature (Ts) is higher by 1–3 degrees vs. the initial ceramic (93 K). SC properties of polymer-ceramic nanocomposites based on Y1Ba2Cu3O6,97 ceramic ( Тpressing=140 оC, pressing=30 min.). Intercalation of the macromolecules or their fragments into the ceramic grain’s interstitial layer is confirmed by NMR tool method (Fig. 1), as well as by studying the dynamical-mechanical properties (Fig. 2) and the morphology of the obtained nanocomposites (Fig. 3). Actually, as it follows from Fig. 1, NMR response precipitately changes upon the variation of the binder’s content. These data speak about the of the copper’s valence state increase from 2 to 2+Δ. Presumably, this is the underlying reason of Ts increase by 1 to 3 degrees. 18
Temperature-to- mechanical-losses’-dissipation-factor interrelation is affected by the presence of Y1Ba2Cu3O6,97 ceramic. This is another confirmation of intercalation that holds true. From Fig. 2 it follows that both the low-temperature (T is ca –130 0C; -100 0C) and high-temperature transition (T is ca 130 0C; 140 0C) Fig2. Temperature dependence of tg for the pure HMPE and for the HMPE ceramic composite. Ceramic content (weight %): curve 1- 0%; 2 – 15%. 19
Intercalation of the macromolecules or their fragments into the ceramic grain’s interstitial layer, obviously, must have an impact on the binder’s morphological structure. Indeed, as it could be seen in Fig. 3, fibrillar structures are formed in the ceramic-binder interface. This is unlike to polyolefin binders. Fig3. Microphotography of polymer-ceramic nano composites at different polymer to ceramic ratio: Y1Ba2Cu3O 6,97 : HMPE =50:50 (a), 70:30 (b) 85:15 (с) 90:10(d). 20
One wanders if it is possible to obtain polymer-ceramic nanocomposites with Meissner effect permitting high load of currents to pass? Addition of nanosized aluminum (30 nm) or silver (40 nm) into the polymer-ceramic composite produces nanocomposites with zero value resistance (Fig. 4). Fig4. Resistance change of the SC polymer ceramic nano composite Y1Ba2Cu3O6,97 with nano aluminum depended on HMPE content 21
Upon the change of binder’s content one could obtain nanaocomposites with 1.6·103 A cm–2 current density loads. Deagglomeration and uniform spatial distribution of nanoparticles increases current density up to 3·103 A cm–2. Fig.5. Dependence of the current density on the binder’s content. It is to be stressed that current-carrying polymer-ceramic nanocomposites have rather good physical-mechanical properties. For example, the following characteristics (ultimate strength is 0.73 kg cm–2; modulus of elasticity is 7.5 kg cm–2; elongation is 2–3%) exhibited a nanocomposite of the formula: Y1Ba2Cu3O 6,97 : binder : nano aluminium = 95 : 3.5 : 1.5. 22
Periodically polled lithium niobate crystals A new technique for creation of periodically polled domain structure in lithium niobate (PPLN) crystals directly during the growth process was developed by the group of Dr.E.Kokanyan at the IPR NASA. The mentioned method was successfully used for the growth of pure as well as doped with various transitional metal and rare-earth impurity ions PPLN crystals. The controlled formation of 4-50m wide domains along the a-axis of the crystals in lengths of 20mm without interruptions or modulations in domain size and with more than 3mm of the domain inversion depth was possible. Scanning election microscope (SEM) micrograph of an etched surface of as-grown hafnium doped lithium niobate crystal. • E.Kokanyan, V.Babajanyan, G.Demirkhanyan, J.Gruber, S.Erdei. J. of Appl. Phys., 92, 1544 (2002). • E.P.Kokanyan, L.Razzari, I.Cristiani, V.Degiorgio and J.B.Gruber. Appl. Phys. Lett., 84, 1880 (2004)
Wavelength converters based on PPLN • Another aspect is a strong limitation to the industrial utilization of wavelength converters based on PPLN crystals, which comes from the so called ‘photorefractive effect’, which induces semi-permanent changes in the refractive index under the light illumination. To redress this problem, at present 5mol% magnesium oxide should be incorporated into lithium niobate. But because of the required very high concentration it makes very difficult to grow good optical quality crystal. • The data obtained by Dr.Kokanyan with co-authors show that tetravalent hafnium ions can be successfully utilized to reduce the photorefractive effect in lithium niobate crystals. Hafnium doping is effective at concentrations much lower than those used with Mg-doping (more than 2 times), potentially allowing crystals with good optical quality and more reproducibly. The micro-Raman results allow assessing a good crystalline quality and a remarkable homogeneity of the Hf-doped lithium niobate crystals. • L.Razzari, P.Minzioni, I.Cristiani, V.Degiorgio, E.P.Kokanyan. Appl. Phys. Lett., 86, 131914 (2005) • E.P.Kokanyan. Ferroelectrics, 341, 119 (2006). • P. Minzioni, I. Cristiani, V. Degiorgio, and E.P. Kokanyan, J. of Appl. Phys., 101, 116105 (2007).
Laser systems and applications in quantum technologies based on periodically-polled nonlinear crystals Periodically-polled nonlinear crystals are very promising for designing of many-line laser systems as well as in areas of applied quantum technologies, including Communication, and Quantum Computation. New laser systems for these goals were theoretically elaborated at Lab. of Quantum Informatics IPR NASA (Prof. Kryuchkyan). This activity also includes investigations of new quasi-periodic structures of nonlinear crystals that realize simultaneous frequency-conversion processes within the same crystal. • H.H. Adamyan, G.Yu. Kryuchkyan, Physical Review A69, 053814 (2004); ibid. A74, 023810 (2006). • N.H. Adamyan, H.H. Adamyan, G.Yu. Kryuchkyan, Physical Review A73, 033810, (2006); ibid A 77, 023820 (2008). International projects:Principal Investigator – E.Kokanyan • INTAS - 94-1080 (1995-1997), 96- 0599 (1998-2000); NFSAT/CRDF- BGP-7431 (2000-2002), AR2-3235 (2006-2008); CRDF-CGP- AP2-2556 (2004-2006); ISTC – A-1033 (2005-2007) Principal Investigator- G..Kryuchkyan • INTAS- 97-1672 (1997-1999), 04-77-7289 (2005-2007); ISTC A-823 (2002-2005), A-1451 (2007-2009), (Submanager); NFSAT PH 098-02 / CRDF 12052 (2002-2004); NFSAT-UCEP 02/07 (2007-2009)