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Papers by Ruben Hovsepyan

The advantages of producing a periodically poled lithium niobate (PPLN) structure during crystal ... more The advantages of producing a periodically poled lithium niobate (PPLN) structure during crystal growth process are the possibility to get thicker and wider structures that leads to greater useful surfaces in addition to the elimination of the subsequent poling process. We report in this paper a new technology of creating bulk periodically poled LiNbO 3 single crystals with antiparallel ferroelectric domains, by direct electric field poling during growth processes. Growth system configuration, crystal composition and geometry selection are explored to allow successful control of the direction of spontaneous polarisation using external electric field. PPLN crystal samples with periodicity 10-200 µm were grown using this electric field modulated growth technique. The photoelectric and photorefractive properties of PPLN crystals were investigated.

Applied Physics B, 2013

A novel combined interferometric-mask method for the formation of micro-and nanometric scale thre... more A novel combined interferometric-mask method for the formation of micro-and nanometric scale three-dimensional (3D) rotational symmetry quasi-crystalline refractive lattice structures in photorefractive materials is demonstrated experimentally. The method is based on micrometric scale spatial modulation of the light by amplitude mask in the radial directions and along the azimuthal angle and the use of counter-propagating beam geometry building up Gaussian standing wave, which defines the light modulation in the axial direction with halfwavelength periodicity. 3D intensity pattern can be represented as numerous mask-generated 2D quasi-periodic structures located in each anti-node of the standing wave. The formed 3D intensity distributions of the optical beams can be imparted into the photorefractive medium thus creating the micro-and sub-micrometric scale 3D refractive index volume lattices. The used optical scheme allows also the formation of 2D lattices by removing the backreflecting mirror. 2D and 3D refractive lattices were recorded with the use of 532 nm laser beam and rotational symmetry mask in doped lithium niobate crystals and were tested by the probe beam far-field diffraction pattern imaging and direct observation by phase microscope. The formed rotational symmetry 3D refractive structures have the periods of 20-60 lm in the radial directions, 60 lm along the azimuthal angle and half-wavelength 266 nm in the axial direction.

Ferroelectrics Letters Section, 2003

... reported. EXPERIMENTAL PROCEDURE Using the traditional growth methods for lithium niobate cry... more ... reported. EXPERIMENTAL PROCEDURE Using the traditional growth methods for lithium niobate crystals, without applying an electrical current through the crystallization front, the direction Page 4. 62 IA GHAMBARYAN et al. of ...

Journal of Applied Physics, 2006

(Pb,La)(Zr,Ti)O3 (PLZT) thin films were grown on Pt/Ti/SiO2/Si and fused quartz substrates by rad... more (Pb,La)(Zr,Ti)O3 (PLZT) thin films were grown on Pt/Ti/SiO2/Si and fused quartz substrates by radio-frequency magnetron sputtering at 650 °C. X-ray diffraction analysis shows that the PLZT films are polycrystalline with (100)-preferential orientation. The Al/PLZT/Pt capacitors have been fabricated and show good ferroelectric properties with the remanent polarization of 24.3 muC/cm2 and coercive field of 142 kV/cm. The leakage current density

SPIE Proceedings, 2010

ABSTRACT Very important advantage of ZnO thin films is an opportunity of use in the composite het... more ABSTRACT Very important advantage of ZnO thin films is an opportunity of use in the composite heterostructures opening opportunities for development of ZnO-based optoelectronics devices. In this work we report the preparation of ferroelectric crystal - ZnO thin film heterostructures by vacuum deposition method and creation of new type of pyroelectric photodetector. The ferroelectric field effect transistor has been prepared using ZnO:Li films as transistor channel and LiNbO(3) and TGS crystals as pyroelectric sensitive element. The photoelectric properties (currents ratio, charge carriers mobility, ampere-watt sensitivity in IR diapason, NEP sensitivity, and photocurrent kinetics) of prepared heterostructures were investigated and first samples of novel pyroelectric photodetector with high sensitivity and detectability were prepared.

Applied Physics A: Materials Science & Processing, 2002

High HfO 2 was deposited on n-type GaN ͑0001͒ using atomic layer deposition with Hf͑NCH 3 C 2 H 5... more High HfO 2 was deposited on n-type GaN ͑0001͒ using atomic layer deposition with Hf͑NCH 3 C 2 H 5 ͒ 4 and H 2 O as the precursors. Excellent electrical properties of TiN / HfO 2 / GaN metal-oxide-semiconductor diode with the oxide thickness of 8.8 nm were obtained, in terms of low electrical leakage current density ͑ϳ10 −6 A/cm 2 at V FB +1 V͒, well behaved capacitance-voltage ͑C-V͒ curves having a low interfacial density of states of 2 ϫ 10 11 cm −2 eV −1 at the midgap, and a high dielectric constant of 16.5. C-V curves with clear accumulation and depletion behaviors were shown, along with negligible frequency dispersion and hysteresis with sweeping biasing voltages. The structural properties studied by high-resolution transmission electron microscopy and x-ray reflectivity show an atomically smooth oxide/GaN interface, with an interfacial layer of GaON ϳ1.8 nm thick, as probed using x-ray photoelectron spectroscopy.

Frontiers in Optics + Laser Science APS/DLS, 2019

A novel method of magnetic field controlled non-destructive testing of optically inducted refract... more A novel method of magnetic field controlled non-destructive testing of optically inducted refractive structures in photorefractive crystals is shown experimentally. Experimental results are explained in the model of polarons in a magnetic field.

Photosensitive Materials and their Applications

We report the trapping of dielectric micro-particles of CaCO3 via dielectrophoretic forces on the... more We report the trapping of dielectric micro-particles of CaCO3 via dielectrophoretic forces on the surface of Fe doped LiNbO3 (LN:Fe) crystal with recorded volume holographic grating which provides quasi-periodic space-charge electric field distribution on the crystal surface. The non-diffracting Bessel beam approach was used for optical induction of holographic grating by 20÷40 mW power Bessel beam at 532 nm wavelength in photorefractive Y-cut LN:Fe crystal providing the Bessel lattice periodicity of ~40 m and hologram size on the crystal surface of 4 mm. This approach provides the induction of high contrast 2D periodic distribution of electric field on the crystal surface and high quality 2D patterning of microparticles. The particles are trapped on the crystal surface in the areas of refractive index maxima of the Bessel lattice. The physical model was developed to explain the experimental results. The photovoltaic approach of trapping and manipulation of micro- and nanoparticles is promising for applications in photonics, integrated optics and biotechnology.

Journal of Contemporary Physics (Armenian Academy of Sciences)

⎯The spectral and luminescent investigations of the Pb(MoO 4) x (WO 4) 1-x crystals doped by the ... more ⎯The spectral and luminescent investigations of the Pb(MoO 4) x (WO 4) 1-x crystals doped by the Nd 3+ ions have been carried out. The investigations have made possible to determine the energies of the Stark levels of the 4 F 3/2 metastable state, 4 I 9/2 ground state, 4 I 11/2 and 4 I 13/2 excited states, as well as the cross section of transitions associated with the intense lines of emission bands in 4 F 3/2 → 4 I 11/2 and 4 F 3/2 → 4 I 13/2 channels. The emission bands in this crystal are relatively wide, so one would expect the creation of a tunable laser and a broadband amplifier in the 1060 and 1330 nm wavelength regions.

Journal of Semiconductor …, 2008

In this work CdS films were prepared by using chemical bath deposition, which is simple and inexp... more In this work CdS films were prepared by using chemical bath deposition, which is simple and inexpensive technique suitable for large deposition area. Annealing in air at different temperatures (300, 350, 400, 450 and 500 °C) at constant time of 30 min, also for different times (15, 30, 45, 60 and 90 min) at constant temperature (300 °C) is achieved. X-Ray analysis has confirmed the formation of cadmium oxide (CdO) with slight increase in grain size, shift towards lower scattering angle due to relaxation in the tensile strain for deposition films, and structure change from cubic and hexagonal to the hexagonal. From electrical properties, significant increase in electrical conductivity appeared in samples annealed at 300 °C for 60 min, and at 350 °C for 30 min.

Optics & Laser Technology

Photonics and Nanostructures - Fundamentals and Applications

Journal of Contemporary Physics (Armenian Academy of Sciences), 2013

⎯Ferroelectric field-effect transistors using ZnO:Li films simultaneously as a transistor channel... more ⎯Ferroelectric field-effect transistors using ZnO:Li films simultaneously as a transistor channel and as a ferroelectric active element have been prepared and studied. We show an opportunity of using the ferroelectric field-effect transistor based on ZnO:Li films in ZnO:Li'LaB 6 heterostructure as a bistable memory element for information recording. The proposed structure of a ferroelectric memory cell does not possess the fatigue under repeated readout of single recorded information that will allow increasing the resource of storage devices essentially.

Journal of Contemporary Physics (Armenian Academy of Sciences), 2012

⎯Metal-insulator electronic phase transitions in wide-gap ZnO semiconductors have been studied. T... more ⎯Metal-insulator electronic phase transitions in wide-gap ZnO semiconductors have been studied. The influence of defect complex caused by oxygen vacancy and interstitial zinc atom on the metal-insulator transition is considered. The peculiarities of this transition in ZnO films doped with donor or acceptor impurity and the influence of mentioned defect complex on the charge carrier transfer mechanism were investigated.

Journal of Contemporary Physics (Armenian Academy of Sciences), 2012

Er 2 O 3 films on sapphire and silicon substrates have been prepared by electron beam evaporation... more Er 2 O 3 films on sapphire and silicon substrates have been prepared by electron beam evaporation technique in vacuum. Preparation of a single-phase erbium oxide film with a cubic lattice and preferred (400) orientation was achieved by means of growth rate decrease. Structural and optical properties of obtained films before and after short-time annealing were investigated. It is shown that the preparation of a single-phase erbium oxide film with a cubic lattice and preferred (222) orientation can be achieved by post-growth annealing of the films grown at usual rates.

Photonic Fiber and Crystal Devices: Advances in Materials and Innovations in Device Applications VII, 2013

ABSTRACT The peculiarities of charge carrier transfer mechanism in ZnO films doped by donor or ac... more ABSTRACT The peculiarities of charge carrier transfer mechanism in ZnO films doped by donor or acceptor impurity and metal-dielectric electronic phase transition were investigated. The control parameter of this transition is concentration of interstitial Zn atoms. The films with high concentration of interstitial Zn atoms have high conductivity of metallic type. Air annealing leads to change of conductivity temperature dependence from metallic type to dielectric one.

Http Dx Doi Org 10 1080 09500340 2013 797611, May 1, 2013

ABSTRACT

The advantages of producing a periodically poled lithium niobate (PPLN) structure during crystal ... more The advantages of producing a periodically poled lithium niobate (PPLN) structure during crystal growth process are the possibility to get thicker and wider structures that leads to greater useful surfaces in addition to the elimination of the subsequent poling process. We report in this paper a new technology of creating bulk periodically poled LiNbO 3 single crystals with antiparallel ferroelectric domains, by direct electric field poling during growth processes. Growth system configuration, crystal composition and geometry selection are explored to allow successful control of the direction of spontaneous polarisation using external electric field. PPLN crystal samples with periodicity 10-200 µm were grown using this electric field modulated growth technique. The photoelectric and photorefractive properties of PPLN crystals were investigated.

Applied Physics B, 2013

A novel combined interferometric-mask method for the formation of micro-and nanometric scale thre... more A novel combined interferometric-mask method for the formation of micro-and nanometric scale three-dimensional (3D) rotational symmetry quasi-crystalline refractive lattice structures in photorefractive materials is demonstrated experimentally. The method is based on micrometric scale spatial modulation of the light by amplitude mask in the radial directions and along the azimuthal angle and the use of counter-propagating beam geometry building up Gaussian standing wave, which defines the light modulation in the axial direction with halfwavelength periodicity. 3D intensity pattern can be represented as numerous mask-generated 2D quasi-periodic structures located in each anti-node of the standing wave. The formed 3D intensity distributions of the optical beams can be imparted into the photorefractive medium thus creating the micro-and sub-micrometric scale 3D refractive index volume lattices. The used optical scheme allows also the formation of 2D lattices by removing the backreflecting mirror. 2D and 3D refractive lattices were recorded with the use of 532 nm laser beam and rotational symmetry mask in doped lithium niobate crystals and were tested by the probe beam far-field diffraction pattern imaging and direct observation by phase microscope. The formed rotational symmetry 3D refractive structures have the periods of 20-60 lm in the radial directions, 60 lm along the azimuthal angle and half-wavelength 266 nm in the axial direction.

Ferroelectrics Letters Section, 2003

... reported. EXPERIMENTAL PROCEDURE Using the traditional growth methods for lithium niobate cry... more ... reported. EXPERIMENTAL PROCEDURE Using the traditional growth methods for lithium niobate crystals, without applying an electrical current through the crystallization front, the direction Page 4. 62 IA GHAMBARYAN et al. of ...

Journal of Applied Physics, 2006

(Pb,La)(Zr,Ti)O3 (PLZT) thin films were grown on Pt/Ti/SiO2/Si and fused quartz substrates by rad... more (Pb,La)(Zr,Ti)O3 (PLZT) thin films were grown on Pt/Ti/SiO2/Si and fused quartz substrates by radio-frequency magnetron sputtering at 650 °C. X-ray diffraction analysis shows that the PLZT films are polycrystalline with (100)-preferential orientation. The Al/PLZT/Pt capacitors have been fabricated and show good ferroelectric properties with the remanent polarization of 24.3 muC/cm2 and coercive field of 142 kV/cm. The leakage current density

SPIE Proceedings, 2010

ABSTRACT Very important advantage of ZnO thin films is an opportunity of use in the composite het... more ABSTRACT Very important advantage of ZnO thin films is an opportunity of use in the composite heterostructures opening opportunities for development of ZnO-based optoelectronics devices. In this work we report the preparation of ferroelectric crystal - ZnO thin film heterostructures by vacuum deposition method and creation of new type of pyroelectric photodetector. The ferroelectric field effect transistor has been prepared using ZnO:Li films as transistor channel and LiNbO(3) and TGS crystals as pyroelectric sensitive element. The photoelectric properties (currents ratio, charge carriers mobility, ampere-watt sensitivity in IR diapason, NEP sensitivity, and photocurrent kinetics) of prepared heterostructures were investigated and first samples of novel pyroelectric photodetector with high sensitivity and detectability were prepared.

Applied Physics A: Materials Science & Processing, 2002

High HfO 2 was deposited on n-type GaN ͑0001͒ using atomic layer deposition with Hf͑NCH 3 C 2 H 5... more High HfO 2 was deposited on n-type GaN ͑0001͒ using atomic layer deposition with Hf͑NCH 3 C 2 H 5 ͒ 4 and H 2 O as the precursors. Excellent electrical properties of TiN / HfO 2 / GaN metal-oxide-semiconductor diode with the oxide thickness of 8.8 nm were obtained, in terms of low electrical leakage current density ͑ϳ10 −6 A/cm 2 at V FB +1 V͒, well behaved capacitance-voltage ͑C-V͒ curves having a low interfacial density of states of 2 ϫ 10 11 cm −2 eV −1 at the midgap, and a high dielectric constant of 16.5. C-V curves with clear accumulation and depletion behaviors were shown, along with negligible frequency dispersion and hysteresis with sweeping biasing voltages. The structural properties studied by high-resolution transmission electron microscopy and x-ray reflectivity show an atomically smooth oxide/GaN interface, with an interfacial layer of GaON ϳ1.8 nm thick, as probed using x-ray photoelectron spectroscopy.

Frontiers in Optics + Laser Science APS/DLS, 2019

A novel method of magnetic field controlled non-destructive testing of optically inducted refract... more A novel method of magnetic field controlled non-destructive testing of optically inducted refractive structures in photorefractive crystals is shown experimentally. Experimental results are explained in the model of polarons in a magnetic field.

Photosensitive Materials and their Applications

We report the trapping of dielectric micro-particles of CaCO3 via dielectrophoretic forces on the... more We report the trapping of dielectric micro-particles of CaCO3 via dielectrophoretic forces on the surface of Fe doped LiNbO3 (LN:Fe) crystal with recorded volume holographic grating which provides quasi-periodic space-charge electric field distribution on the crystal surface. The non-diffracting Bessel beam approach was used for optical induction of holographic grating by 20÷40 mW power Bessel beam at 532 nm wavelength in photorefractive Y-cut LN:Fe crystal providing the Bessel lattice periodicity of ~40 m and hologram size on the crystal surface of 4 mm. This approach provides the induction of high contrast 2D periodic distribution of electric field on the crystal surface and high quality 2D patterning of microparticles. The particles are trapped on the crystal surface in the areas of refractive index maxima of the Bessel lattice. The physical model was developed to explain the experimental results. The photovoltaic approach of trapping and manipulation of micro- and nanoparticles is promising for applications in photonics, integrated optics and biotechnology.

Journal of Contemporary Physics (Armenian Academy of Sciences)

⎯The spectral and luminescent investigations of the Pb(MoO 4) x (WO 4) 1-x crystals doped by the ... more ⎯The spectral and luminescent investigations of the Pb(MoO 4) x (WO 4) 1-x crystals doped by the Nd 3+ ions have been carried out. The investigations have made possible to determine the energies of the Stark levels of the 4 F 3/2 metastable state, 4 I 9/2 ground state, 4 I 11/2 and 4 I 13/2 excited states, as well as the cross section of transitions associated with the intense lines of emission bands in 4 F 3/2 → 4 I 11/2 and 4 F 3/2 → 4 I 13/2 channels. The emission bands in this crystal are relatively wide, so one would expect the creation of a tunable laser and a broadband amplifier in the 1060 and 1330 nm wavelength regions.

Journal of Semiconductor …, 2008

In this work CdS films were prepared by using chemical bath deposition, which is simple and inexp... more In this work CdS films were prepared by using chemical bath deposition, which is simple and inexpensive technique suitable for large deposition area. Annealing in air at different temperatures (300, 350, 400, 450 and 500 °C) at constant time of 30 min, also for different times (15, 30, 45, 60 and 90 min) at constant temperature (300 °C) is achieved. X-Ray analysis has confirmed the formation of cadmium oxide (CdO) with slight increase in grain size, shift towards lower scattering angle due to relaxation in the tensile strain for deposition films, and structure change from cubic and hexagonal to the hexagonal. From electrical properties, significant increase in electrical conductivity appeared in samples annealed at 300 °C for 60 min, and at 350 °C for 30 min.

Optics & Laser Technology

Photonics and Nanostructures - Fundamentals and Applications

Journal of Contemporary Physics (Armenian Academy of Sciences), 2013

⎯Ferroelectric field-effect transistors using ZnO:Li films simultaneously as a transistor channel... more ⎯Ferroelectric field-effect transistors using ZnO:Li films simultaneously as a transistor channel and as a ferroelectric active element have been prepared and studied. We show an opportunity of using the ferroelectric field-effect transistor based on ZnO:Li films in ZnO:Li'LaB 6 heterostructure as a bistable memory element for information recording. The proposed structure of a ferroelectric memory cell does not possess the fatigue under repeated readout of single recorded information that will allow increasing the resource of storage devices essentially.

Journal of Contemporary Physics (Armenian Academy of Sciences), 2012

⎯Metal-insulator electronic phase transitions in wide-gap ZnO semiconductors have been studied. T... more ⎯Metal-insulator electronic phase transitions in wide-gap ZnO semiconductors have been studied. The influence of defect complex caused by oxygen vacancy and interstitial zinc atom on the metal-insulator transition is considered. The peculiarities of this transition in ZnO films doped with donor or acceptor impurity and the influence of mentioned defect complex on the charge carrier transfer mechanism were investigated.

Journal of Contemporary Physics (Armenian Academy of Sciences), 2012

Er 2 O 3 films on sapphire and silicon substrates have been prepared by electron beam evaporation... more Er 2 O 3 films on sapphire and silicon substrates have been prepared by electron beam evaporation technique in vacuum. Preparation of a single-phase erbium oxide film with a cubic lattice and preferred (400) orientation was achieved by means of growth rate decrease. Structural and optical properties of obtained films before and after short-time annealing were investigated. It is shown that the preparation of a single-phase erbium oxide film with a cubic lattice and preferred (222) orientation can be achieved by post-growth annealing of the films grown at usual rates.

Photonic Fiber and Crystal Devices: Advances in Materials and Innovations in Device Applications VII, 2013

ABSTRACT The peculiarities of charge carrier transfer mechanism in ZnO films doped by donor or ac... more ABSTRACT The peculiarities of charge carrier transfer mechanism in ZnO films doped by donor or acceptor impurity and metal-dielectric electronic phase transition were investigated. The control parameter of this transition is concentration of interstitial Zn atoms. The films with high concentration of interstitial Zn atoms have high conductivity of metallic type. Air annealing leads to change of conductivity temperature dependence from metallic type to dielectric one.

Http Dx Doi Org 10 1080 09500340 2013 797611, May 1, 2013

ABSTRACT