RUSSIAN-ARMENIAN STATE UNIVERSITY

PHYSICO-TECHNICAL DEPARTMENT

Ovsep Emin Str.123,Yerevan, Armenia

Prof. Stepan Petrosyan

email: spetrosyan@rau.am

Dr. Vladimir Gevorkyan

email: vgev@rau.am

Field of Scientific Activities

• 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)

Novel diode heterostructures on the base

of InAs alloys

Fields of applications

Methane Sensors:

for methane leakage in houses, along gas communications, in

mines

Systems of optical fibres

communicationFree-space optical

link

Mid IRPhotodiodes

Medical Diagnostics:glucose and other

substances in blood, in tissue

Medical Diagnostics:

Carbon Dioxide,Acetone and

gases in breath

Energy production and energy-saving applications

Thermophotovoltaic

Water Sensors:water in paper,water in grain,

water in oil products.

Ecologicalmonitoring of

different industrial

pollutants in air and water

Thermophotovoltaic converters

Source of

thermal or solar energy

Heated body

(emitter)1000-

2000ОС

Selective optical

filter/reflector

TPV cell(Eg)

Backside reflector

ħ ω<Eg

ħ ω<Eg

Focusing Lens system

Sun 60000C

TPV Energy

Converter

Sourc

es

of

Ene

rgy

Solar

Energ

y

Therm

al En

ergy

HYDROGEN

GAS

FUEL

ATOMIC ENERGY

INDUSTRIAL WASTE HEAT

Sources of solar and thermal energy for direct conversion to

electricity on the base of TPV cells

Frenel Lens

Mirror

Emitter T~12000C

TPV Cell

Back Surface Reflector

Vacuum

Optical Selective Filter

Secondary lens

Water (or forced air) Heat Exchanger

Engineering model of solar energy converter on the base of TPV cell

Relative spectral response of the n+-InAs / n0-InAs / p+- InAs0.27Sb0.23P0.5 TPV diode

heterostructure grown by non-equilibrium MOVPE growth

technique

1.0 1.5 2.0 2.5 3.0 3.5 4.00

10

20

30

40

50

60

70

80

90

100

=2.2-3.6 m

th=3.8 m

t = +22CSOS201

Spec

tral re

spon

se, a

rb.u.

Wavelength, , m

Smax = 1.4 - 1.6 A/W

= 0.4 - 0.5Flexibility of the heat source, which includes solar and other thermal sources of energyCompact in sizeLight weight Low Noise TPV converters can provide 24 hours of electricity due to combining solar energy and thermal energy (combustion flame, etc.).

Amplifier

Photo-diode Chip

Sapphire Window

Schematic view and photo of an engineering

model of infrared photo-diode.

Packaged Mid-IR

photo-diode.

Mid-Infrared photodiodes

Epitaxial film

ready 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.

E

g2

EC

E

F

ħω

EV

E

g1

n-InAsSubstrate

p-InAs1-x-

yPySbx emitter layer

Band diagram of the n-InAs/p-InAs1-

x-yPxSby TPV diode heterostructure

Quantum Dot Solar Cell:

Structure

(a) Schematic diagram of QDSC

(b) Corresponding energy band structure

Quantum Dot Solar Cell: Results

Theoretical results

Experimental results

1. Photocurrent density versus number of stacked layers compared with the photocurrent without QD’s.

2. 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

2D Shchottky contact

+ + +

+ + +

+ + +

+ + +

+ + +

+ + +

+ + +

+ + +

+ + +

+ + +

-

-

-

-

-

-

-

-

-

x

z

2ДЭГ2Д Металл

l

0

04bi A

s

V Ven

VA= 0

VА=-4 eV

VА=4 eV

(x)

2D electron gas field efect transistor

x

yL

2a

V(y)

+ + + +++

+ + +++ + +

VG

VG

VS

VD

W(y)

W(y)

2GV eV

3GV eV

1GV eV

4GV eV

GPbi

DVV

V

0DSAT

D

I

I0GV

• High channel conductivity

• Very high transconductance.

2DEG

Laser Synthesis of the Colloidal Nanoparticles

•Semiconductor Nanoparticles (Quantum Dots)

•Metal Nanoparticles

•Carbon Nanoparticles

•Polymer Nanoparticles

Laser ablation of materials in liquids

TechniqueApplied:

Blue -Ultraviolet LuminescenceUltrafine Sizes: 2-3nm

I ,L a .u .

W a v e le n g th , n m

C d S

4 00 4 20 4 40 4 60 4 80

I , L a .u .

W a v e le n g th , n m

G a A s

4 00 4 20 4 40 4 60

2

2 2

2MRE

Quantum Dots

In a frog embryo has been imaged using (a) organic-dye techniques (b) Quantum Dots

The capillary structure, is revealed with fluorescence microscopy as nanocrystal quantum dots circulate through the bloodstream.

Ultrafine nano[particles in biological imaging

An important aspect of QD labels is their extremely high photostability, which allows monitoring of intra-cellular processes over long periods of time

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 enoughto pass through the capillary systems of organs and tissues

• Their movement in the blood can be controlled with a magnetic field

The ability to engineer nanoassemblies promise for a new generation of electronics, and optoelectronics

•plasmonic subwavelength waveguiding•Plasmonicoptoelectronics

Nanofibers Carbon Micro/Nanofibers

Nanostructures

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 % .

2

4, 5

1

6

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

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).

Composition Weight ratio of ceramic and binder Ts,K Tf,

K

SHMPE + Y1Ba2Cu3O6,97 80 : 2085 : 1585 : 15

969696

848484

RPE+ Y1Ba2Cu3O6,97 80 : 20 94 80

F-40+ Y1Ba2Cu3O6,97 75 : 25 96 77

PB+ Y1Ba2Cu3O6,97 80 : 20 96 83

PVIF+ Y1Ba2Cu3O6,97 85 : 15 90 75

PF+ Y1Ba2Cu3O6,97 80 : 20 88 76

HMPE+irgonaks+ Y1Ba2Cu3O6,97 80 : 20 96 89

RPE+ irgonaks + Y1Ba2Cu3O6,97 80 : 20 94 85

PVA+ irganoks + Y1Ba2Cu3O6,97 85 : 15 90 80

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.

19

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%.

20

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).

21

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

22

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.

Periodically polled lithium niobate crystals

Scanning election microscope (SEM) micrograph of an etched surface of as-grown hafnium doped lithium niobate crystal.

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.

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)