ABSTRACTSwitching from superconducting (S) to normal (N) state was investigated using short rise ... more ABSTRACTSwitching from superconducting (S) to normal (N) state was investigated using short rise time (∼ 10−10 s) electric pulses in MBE grown Bi-Sr-Ca-Cu-O and rf magnetron sputtered Y-Ba-Cu-O submicron thickness microstrips. It was found that two reversible processes: fast electronic (τ∼10∼−12 s) and slow thermal (τ∼10∼−8s) one take place during switching. At high current densities (∼107 A/cm2) irreversible changes in strip material induced by thermal runaway occurred. The use of a superconducting element as fast fault-current limiter or pulse sharpening device is pointed out.
We report on the synthesis of two naphthalene diimide-based organic derivatives: POANT containing... more We report on the synthesis of two naphthalene diimide-based organic derivatives: POANT containing electronically isolated 1,4,5,8-naphthalenetetracarboxylic diimide units and FCAND – a low-molar-mass compound with two different (fluorenone and 1,4,5,8-naphthalenetetracarboxylic diimide) electron-accepting units. Initial decomposition temperatures of 305°C and 390°C were indicated for FCAND and POANT, respectively. Organic semiconductor/Si heterostructures have been prepared by using spin coating (POANT, PEPK) and
We report preparation and investigation of p-n heterostructures based on Fe3O4 thin films grown o... more We report preparation and investigation of p-n heterostructures based on Fe3O4 thin films grown on n-Si(111) substrates as well as indium oxide (IO) and tin doped indium oxide (ITO) layers deposited on lattice-matched monocrystalline ZrO2:Y2O3(100). Thin Fe3O4 films with thickness ranging from 100 to 300 nm were grown in situ at 400 K using dc magnetron sputtering technique. The measurement of microstructure revealed polycrystalline quality of Fe3O4 films on silicon substrate and epitaxial growth on (IO)ITO/YSZ. Investigation of surface composition by X-ray Photoelectron Spectroscopy (XPS) showed that Fe 2p peak consists of three main peaks, namely, metallic iron Fe(0), Fe(II) and Fe(III). Transport measurements of Fe3O4/n-Si heterostructures demonstrated rectifying behaviour in a wide temperature range (T = 78÷300 K) while those prepared by growing Fe3O4 layers on indium oxide (IO) demonstrated nonlinear current-voltage (I-V) dependencies at low temperatures (T<120K).
Fabry–Perot laser diodes based on (Al, Ga)As and Ga(As, Bi) with single or multiple parabolic or ... more Fabry–Perot laser diodes based on (Al, Ga)As and Ga(As, Bi) with single or multiple parabolic or rectangular-shaped quantum wells (QWs) emitting at the 780–1100 nm spectral range were fabricated and investigated for optimization of the laser QW design and composition of QWs. The laser structures were grown using the molecular beam epitaxy (MBE) technique on the n-type GaAs(100) substrate. The photolithography process was performed to fabricate edge-emitting laser bars of 5 μm by 500 μm in size. The temperature-dependent power-current measurements showed that the characteristic threshold current of the fabricated LDs was in the 60–120 mA range. Light and current characteristics were almost linear up to (1.2–2.0) Ith. Low-frequency 10 Hz–20 kHz electrical and optical noise characteristics were measured in the temperature range from 70 K to 290 K and showed that the low-frequency optical and electrical noise spectra are comprised of 1/f and Lorentzian-type components. The positive cros...
A set of single quantum well (SQW) samples of GaAs1-xBix with x ~ 0.1 and p-doped GaAs barriers g... more A set of single quantum well (SQW) samples of GaAs1-xBix with x ~ 0.1 and p-doped GaAs barriers grown by molecular beam epitaxy was investigated by the temperature-dependent photoluminescence (PL) spectroscopy. Those GaAsBi SQW structures showed a high crystalline quality, a smooth surface and sharp interfaces between the layers and exhibited a high PL intensity and a lower than 100 meV PL linewidth of QW structures. Temperature dependence of the optical transition energy was S-shape-free for all investigated structures and it was weaker than that of GaAs. An analysis of the carrier recombination mechanism was also carried out indicating that the radiative recombination is dominant even at room temperature. Moreover, numerical calculations revealed that a higher Be doping concentration leads to an increased overlap of the electron and heavy hole wave functions and determines a higher PL intensity.
ABSTRACT In this work, we demonstrate an improvement of c-Si solar cell properties by using conce... more ABSTRACT In this work, we demonstrate an improvement of c-Si solar cell properties by using concept of three-dimensional (3D) c-Si solar cell technology that results in an enhancement of the conversion of the sun light into the electric current. Technological method for concept realization is based on the p-n junction that is formed on the textured side of the substrate by the diffusion assisted doping from the phosphosilicate glass. Before doping an array of nano-holes, nano-cones or nano-hills is fabricated by electrochemical and chemical etching of the p-Si substrate. In this work, a relationship between the technological conditions and the fundamental properties of the cells is investigated. An influence of the etching conditions on the cell structure, the junction formation and the electrical parameters is discussed.
GaAsBi is a suitable and very attractive material system to be used as an active layer in laser d... more GaAsBi is a suitable and very attractive material system to be used as an active layer in laser diodes (LDs). To understand the performance and the reliability of such devices and also for further laser diode improvements, the origin of noise sources should be clarified. A detailed study of near-infrared 1.09 μm wavelength GaAsBi type-I laser diodes using the low-frequency noise spectroscopy in a temperature range of (180–300) K is presented. Different types of voltage fluctuation spectral density dependencies on the forward current far below the lasing threshold have been observed. According to this, investigated samples have been classified into two groups and two equivalent noise circuits with the corresponding voltage noise sources are presented. Calculations on the voltage spectral density of the electrical noise and current-voltage characteristic approximations have been performed and the results are consistent with the experimental data. The analysis showed that one group of ...
A series of 1.5 μm-thick epitaxial GaAsBi layers have been grown by molecular beam epitaxy on sem... more A series of 1.5 μm-thick epitaxial GaAsBi layers have been grown by molecular beam epitaxy on semi-insulating GaAs(100) substrates at temperatures ranging from 300 to 370°C. Complex studies were carried out with a focus to optimize the technological parameters for application of these layers in photoconductive THz components. The investigation of crystalline structure, layer morphology, optical properties, and characteristics of carrier dynamics was performed. Up to 12% of Bi incorporation has been confirmed by optical and structural analyses of GaAsBi layers grown at relatively low temperatures of about 300°C. The carrier lifetimes of these layers varied from 1 to 3 ps. Thick GaAsBi layers grown at higher than 350°C temperatures exhibited higher crystalline quality and longer carrier lifetimes reaching even tens of picoseconds. The Bi content in high-temperature-grown GaAsBi varied from 3 to 7% Bi.
Crystallographic properties of AlAs barriers in GaAsBi-based multi-quantum well structures grown ... more Crystallographic properties of AlAs barriers in GaAsBi-based multi-quantum well structures grown on GaAs substrates by molecular beam epitaxy (MBE) and migration-enhanced epitaxy (MEE) were studied. The quantum wells were grown at temperatures ranging from 160 to 350 °C. The width of GaAsBi quantum wells varied from 4 to 20 nm. The optimization of technological parameters for the growth of high crystalline quality AlAs barriers at low temperatures was performed. To explore the impact of high temperature treatment on crystal quality, surface roughness and chemical composition stability, ex situ rapid thermal annealing was performed at 650–750 °C for 180 s in nitrogen ambiance. The structural quality of AlAs barriers, the morphology and sharpness of the interfaces between GaAsBi quantum wells and AlAs barriers were studied by high resolution X-ray diffraction, atomic force microscopy and high resolution transmission electron microscopy, respectively. In this study it was demonstrated ...
Formation of bismuth nanocrystals in GaAsBi layers grown by molecular beam epitaxy at 330 °C subs... more Formation of bismuth nanocrystals in GaAsBi layers grown by molecular beam epitaxy at 330 °C substrate temperature and post-growth annealed at 750 °C is reported. Superlattices containing alternating 10 nm-thick GaAsBi and AlAs layers were grown on semi-insulating GaAs substrate. AlAs layers have served as diffusion barriers for Bi atoms, and the size of the nanoclusters which nucleated after sample annealing was correlating with the thickness of the bismide layers. Energy-dispersive spectroscopy and Raman scattering measurements have evidenced that the nanoparticles predominantly constituted from Bi atoms. Strong photoluminescence signal with photon wavelengths ranging from 1.3 to 1.7 μm was observed after annealing; its amplitude was scaling-up with the increased number of the GaAsBi layers. The observed photoluminescence band can be due to emission from Bi nanocrystals. The carried out theoretical estimates support the assumption. They show that due to the quantum size effect, th...
A series of 100 nm-thick pseudomorphic GaAsBi layers with the Bi content varying from 0.97 to 11.... more A series of 100 nm-thick pseudomorphic GaAsBi layers with the Bi content varying from 0.97 to 11.2% have been grown by molecular beam epitaxy (MBE) on the semi-insulating GaAs(100) substrates buffered with an ultra-thin up to 20 nm thick GaAs layer. The main attention in this work was focused on the investigation of relaxation in the Bi induced compressively-strained GaAsBi layers containing a various content of Bi. The lattice parameters of GaAs- Bi compound and the Bi concentration have been evaluated from high resolution X-ray diffraction measurements. The relaxation values of GaAsBi layers ranging from 0.4 to 3.5% were obtained analyzing the symmetric and asymmetric reciprocal space maps of (004) and (115) planes, respectively. Also, the complex study was performed to clarify the relaxation effect on structural, morphological and optical properties of bismide layers. Optical measurements revealed a significant reduction of the energy band gap from 1.34 to 0.92 eV for the layers ...
InGaAs-based bow-tie diodes for the terahertz (THz) range are found to be well suited for develop... more InGaAs-based bow-tie diodes for the terahertz (THz) range are found to be well suited for development of compact THz imaging systems. To further optimize design for sensitive and broadband THz detection, one of the major challenges remains: to understand the noise origin, influence of growth conditions and role of defects for device operation. We present a detailed study of photoreflectance, low-frequency noise characteristics and THz sensitivity of InGaAs bow-tie diodes. The diodes are fabricated from InGaAs wafers grown by molecular beam epitaxy (MBE) on semi-insulating InP substrate under different technological conditions. Photoreflectance spectra indicated the presence of strong built-in electric fields reaching up to 49 kV/cm. It was demonstrated that the spectral density of voltage fluctuations at room temperature was found to be proportional to 1/f, while at lower temperatures, 77–200 K, Lorentzian-type spectra dominate due to random telegraph signals caused by individual ca...
ABSTRACTSwitching from superconducting (S) to normal (N) state was investigated using short rise ... more ABSTRACTSwitching from superconducting (S) to normal (N) state was investigated using short rise time (∼ 10−10 s) electric pulses in MBE grown Bi-Sr-Ca-Cu-O and rf magnetron sputtered Y-Ba-Cu-O submicron thickness microstrips. It was found that two reversible processes: fast electronic (τ∼10∼−12 s) and slow thermal (τ∼10∼−8s) one take place during switching. At high current densities (∼107 A/cm2) irreversible changes in strip material induced by thermal runaway occurred. The use of a superconducting element as fast fault-current limiter or pulse sharpening device is pointed out.
We report on the synthesis of two naphthalene diimide-based organic derivatives: POANT containing... more We report on the synthesis of two naphthalene diimide-based organic derivatives: POANT containing electronically isolated 1,4,5,8-naphthalenetetracarboxylic diimide units and FCAND – a low-molar-mass compound with two different (fluorenone and 1,4,5,8-naphthalenetetracarboxylic diimide) electron-accepting units. Initial decomposition temperatures of 305°C and 390°C were indicated for FCAND and POANT, respectively. Organic semiconductor/Si heterostructures have been prepared by using spin coating (POANT, PEPK) and
We report preparation and investigation of p-n heterostructures based on Fe3O4 thin films grown o... more We report preparation and investigation of p-n heterostructures based on Fe3O4 thin films grown on n-Si(111) substrates as well as indium oxide (IO) and tin doped indium oxide (ITO) layers deposited on lattice-matched monocrystalline ZrO2:Y2O3(100). Thin Fe3O4 films with thickness ranging from 100 to 300 nm were grown in situ at 400 K using dc magnetron sputtering technique. The measurement of microstructure revealed polycrystalline quality of Fe3O4 films on silicon substrate and epitaxial growth on (IO)ITO/YSZ. Investigation of surface composition by X-ray Photoelectron Spectroscopy (XPS) showed that Fe 2p peak consists of three main peaks, namely, metallic iron Fe(0), Fe(II) and Fe(III). Transport measurements of Fe3O4/n-Si heterostructures demonstrated rectifying behaviour in a wide temperature range (T = 78÷300 K) while those prepared by growing Fe3O4 layers on indium oxide (IO) demonstrated nonlinear current-voltage (I-V) dependencies at low temperatures (T<120K).
Fabry–Perot laser diodes based on (Al, Ga)As and Ga(As, Bi) with single or multiple parabolic or ... more Fabry–Perot laser diodes based on (Al, Ga)As and Ga(As, Bi) with single or multiple parabolic or rectangular-shaped quantum wells (QWs) emitting at the 780–1100 nm spectral range were fabricated and investigated for optimization of the laser QW design and composition of QWs. The laser structures were grown using the molecular beam epitaxy (MBE) technique on the n-type GaAs(100) substrate. The photolithography process was performed to fabricate edge-emitting laser bars of 5 μm by 500 μm in size. The temperature-dependent power-current measurements showed that the characteristic threshold current of the fabricated LDs was in the 60–120 mA range. Light and current characteristics were almost linear up to (1.2–2.0) Ith. Low-frequency 10 Hz–20 kHz electrical and optical noise characteristics were measured in the temperature range from 70 K to 290 K and showed that the low-frequency optical and electrical noise spectra are comprised of 1/f and Lorentzian-type components. The positive cros...
A set of single quantum well (SQW) samples of GaAs1-xBix with x ~ 0.1 and p-doped GaAs barriers g... more A set of single quantum well (SQW) samples of GaAs1-xBix with x ~ 0.1 and p-doped GaAs barriers grown by molecular beam epitaxy was investigated by the temperature-dependent photoluminescence (PL) spectroscopy. Those GaAsBi SQW structures showed a high crystalline quality, a smooth surface and sharp interfaces between the layers and exhibited a high PL intensity and a lower than 100 meV PL linewidth of QW structures. Temperature dependence of the optical transition energy was S-shape-free for all investigated structures and it was weaker than that of GaAs. An analysis of the carrier recombination mechanism was also carried out indicating that the radiative recombination is dominant even at room temperature. Moreover, numerical calculations revealed that a higher Be doping concentration leads to an increased overlap of the electron and heavy hole wave functions and determines a higher PL intensity.
ABSTRACT In this work, we demonstrate an improvement of c-Si solar cell properties by using conce... more ABSTRACT In this work, we demonstrate an improvement of c-Si solar cell properties by using concept of three-dimensional (3D) c-Si solar cell technology that results in an enhancement of the conversion of the sun light into the electric current. Technological method for concept realization is based on the p-n junction that is formed on the textured side of the substrate by the diffusion assisted doping from the phosphosilicate glass. Before doping an array of nano-holes, nano-cones or nano-hills is fabricated by electrochemical and chemical etching of the p-Si substrate. In this work, a relationship between the technological conditions and the fundamental properties of the cells is investigated. An influence of the etching conditions on the cell structure, the junction formation and the electrical parameters is discussed.
GaAsBi is a suitable and very attractive material system to be used as an active layer in laser d... more GaAsBi is a suitable and very attractive material system to be used as an active layer in laser diodes (LDs). To understand the performance and the reliability of such devices and also for further laser diode improvements, the origin of noise sources should be clarified. A detailed study of near-infrared 1.09 μm wavelength GaAsBi type-I laser diodes using the low-frequency noise spectroscopy in a temperature range of (180–300) K is presented. Different types of voltage fluctuation spectral density dependencies on the forward current far below the lasing threshold have been observed. According to this, investigated samples have been classified into two groups and two equivalent noise circuits with the corresponding voltage noise sources are presented. Calculations on the voltage spectral density of the electrical noise and current-voltage characteristic approximations have been performed and the results are consistent with the experimental data. The analysis showed that one group of ...
A series of 1.5 μm-thick epitaxial GaAsBi layers have been grown by molecular beam epitaxy on sem... more A series of 1.5 μm-thick epitaxial GaAsBi layers have been grown by molecular beam epitaxy on semi-insulating GaAs(100) substrates at temperatures ranging from 300 to 370°C. Complex studies were carried out with a focus to optimize the technological parameters for application of these layers in photoconductive THz components. The investigation of crystalline structure, layer morphology, optical properties, and characteristics of carrier dynamics was performed. Up to 12% of Bi incorporation has been confirmed by optical and structural analyses of GaAsBi layers grown at relatively low temperatures of about 300°C. The carrier lifetimes of these layers varied from 1 to 3 ps. Thick GaAsBi layers grown at higher than 350°C temperatures exhibited higher crystalline quality and longer carrier lifetimes reaching even tens of picoseconds. The Bi content in high-temperature-grown GaAsBi varied from 3 to 7% Bi.
Crystallographic properties of AlAs barriers in GaAsBi-based multi-quantum well structures grown ... more Crystallographic properties of AlAs barriers in GaAsBi-based multi-quantum well structures grown on GaAs substrates by molecular beam epitaxy (MBE) and migration-enhanced epitaxy (MEE) were studied. The quantum wells were grown at temperatures ranging from 160 to 350 °C. The width of GaAsBi quantum wells varied from 4 to 20 nm. The optimization of technological parameters for the growth of high crystalline quality AlAs barriers at low temperatures was performed. To explore the impact of high temperature treatment on crystal quality, surface roughness and chemical composition stability, ex situ rapid thermal annealing was performed at 650–750 °C for 180 s in nitrogen ambiance. The structural quality of AlAs barriers, the morphology and sharpness of the interfaces between GaAsBi quantum wells and AlAs barriers were studied by high resolution X-ray diffraction, atomic force microscopy and high resolution transmission electron microscopy, respectively. In this study it was demonstrated ...
Formation of bismuth nanocrystals in GaAsBi layers grown by molecular beam epitaxy at 330 °C subs... more Formation of bismuth nanocrystals in GaAsBi layers grown by molecular beam epitaxy at 330 °C substrate temperature and post-growth annealed at 750 °C is reported. Superlattices containing alternating 10 nm-thick GaAsBi and AlAs layers were grown on semi-insulating GaAs substrate. AlAs layers have served as diffusion barriers for Bi atoms, and the size of the nanoclusters which nucleated after sample annealing was correlating with the thickness of the bismide layers. Energy-dispersive spectroscopy and Raman scattering measurements have evidenced that the nanoparticles predominantly constituted from Bi atoms. Strong photoluminescence signal with photon wavelengths ranging from 1.3 to 1.7 μm was observed after annealing; its amplitude was scaling-up with the increased number of the GaAsBi layers. The observed photoluminescence band can be due to emission from Bi nanocrystals. The carried out theoretical estimates support the assumption. They show that due to the quantum size effect, th...
A series of 100 nm-thick pseudomorphic GaAsBi layers with the Bi content varying from 0.97 to 11.... more A series of 100 nm-thick pseudomorphic GaAsBi layers with the Bi content varying from 0.97 to 11.2% have been grown by molecular beam epitaxy (MBE) on the semi-insulating GaAs(100) substrates buffered with an ultra-thin up to 20 nm thick GaAs layer. The main attention in this work was focused on the investigation of relaxation in the Bi induced compressively-strained GaAsBi layers containing a various content of Bi. The lattice parameters of GaAs- Bi compound and the Bi concentration have been evaluated from high resolution X-ray diffraction measurements. The relaxation values of GaAsBi layers ranging from 0.4 to 3.5% were obtained analyzing the symmetric and asymmetric reciprocal space maps of (004) and (115) planes, respectively. Also, the complex study was performed to clarify the relaxation effect on structural, morphological and optical properties of bismide layers. Optical measurements revealed a significant reduction of the energy band gap from 1.34 to 0.92 eV for the layers ...
InGaAs-based bow-tie diodes for the terahertz (THz) range are found to be well suited for develop... more InGaAs-based bow-tie diodes for the terahertz (THz) range are found to be well suited for development of compact THz imaging systems. To further optimize design for sensitive and broadband THz detection, one of the major challenges remains: to understand the noise origin, influence of growth conditions and role of defects for device operation. We present a detailed study of photoreflectance, low-frequency noise characteristics and THz sensitivity of InGaAs bow-tie diodes. The diodes are fabricated from InGaAs wafers grown by molecular beam epitaxy (MBE) on semi-insulating InP substrate under different technological conditions. Photoreflectance spectra indicated the presence of strong built-in electric fields reaching up to 49 kV/cm. It was demonstrated that the spectral density of voltage fluctuations at room temperature was found to be proportional to 1/f, while at lower temperatures, 77–200 K, Lorentzian-type spectra dominate due to random telegraph signals caused by individual ca...
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Papers by Renata Butkute