Stanislav Hasenöhrl - Academia.edu (original) (raw)
Papers by Stanislav Hasenöhrl
Indium Phosphide and Related Materials Conference, 2002
A modified wagon-wheel-mask technique was used to determine data for the reconstruction of a pola... more A modified wagon-wheel-mask technique was used to determine data for the reconstruction of a polar diagram of InP crystal wet etched in etchants based on HCl and H3PO4. It is demonstrated that the facet revelation and mask underetching within ±5° around [001] are very sensitive to the etchant composition as well as to mask orientation.
The Ninth International Conference on Advanced Semiconductor Devices and Mircosystems, 2012
ABSTRACT GaP/ZnO core-shell nanowires were prepared by Metal Organic Vapour Phase Epitaxy and RF ... more ABSTRACT GaP/ZnO core-shell nanowires were prepared by Metal Organic Vapour Phase Epitaxy and RF sputtering. We studied systematically room temperature photoluminescence of the NWs in the ultraviolet and green regions. Our study revealed that the UV peak position shifted slightly towards longer wavelengths while the green emission with the main transition at 2.25eV was almost unchanged.
Proceedings of 8th International Conference on Indium Phosphide and Related Materials
Currently, resonant cavity enhanced (RCE) photodetectors have received a great deal of attention ... more Currently, resonant cavity enhanced (RCE) photodetectors have received a great deal of attention for applications of photoreceivers with wavelength-selective capabilities and higher bandwith efficiency product. In the present work, we report on the design, growth and properties of RCE PIN photodiodes for 1300 nm wavelength region using In 0.52Al0.21Ga0.27As/InP bottom mirror overgrown by In0.53Ga0.47As/InP PIN photodiode
2008 International Conference on Advanced Semiconductor Devices and Microsystems, 2008
Extensive numerical experiments have shown that the iteratively reweighted 1 minimization algorit... more Extensive numerical experiments have shown that the iteratively reweighted 1 minimization algorithm (IRL1) is a very efficient method for variable selection, signal reconstruction and image processing. However no convergence results have been given for the IRL1. In this paper, we first give a global convergence theorem of the IRL1 for the 2p (0 < p < 1) minimization problem. We prove that any sequence generated by the IRL1 converges to a stationary point of the 2p minimization problem. Moreover, the stationary point is a global minimizer in certain domain and the convergence rate is approximately linear under certain conditions. We derive posteriori error bounds which can be used to construct practical stopping rules for the algorithm. Other contribution of this paper is to prove the uniqueness of solution of the truncated p minimization problem under the truncated null space property which is weaker than the restricted isometry property.
The Ninth International Conference on Advanced Semiconductor Devices and Mircosystems, 2012
ABSTRACT We have studied the properties of the prepared ZnO thin films on GaP nanowires deposited... more ABSTRACT We have studied the properties of the prepared ZnO thin films on GaP nanowires deposited by reactive magnetron sputtering at different target-substrate geometry and deposition conditions. ZnO/GaP-NW core-shell structures were created on MOCVD-GaP NWs grown on Zn-doped GaP(111)B substrates. Some important physical properties of the ZnO films and core-shell GaP/ZnO heterojunctions were investigated.
Applied Surface Science, 2017
Indium nitride (InN) is a very promising direct bandgap semiconductor material for near-infrared ... more Indium nitride (InN) is a very promising direct bandgap semiconductor material for near-infrared optoelectronic devices and high speed transistors, however InN growth is much more challenging compared to other III-N semiconductors. In this study we analysed the impact of pre-growth vicinal c-plane sapphire substrate nitridation on the electrical, optical, and strucutral properties of N-polar InN/InAlN heterostructures and the InN crystal habit. While a short cool-down nitridation phase resulted in a high quality InAlN layer and low quality InN layer, it was the opposite for a long cool-down nitridation phase. A trade-off between the electrical and optical properties was observed: the short nitridation cool-down produced InN layers with a higher electron mobility of 629 cm2 V−1 s−1 and low photoluminescence (PL) emission, and the long one resulted in InN with a ∼21% lower electron mobility of 497 cm2 V−1s−1 but strong PL emission. Also, a very different InN crystal habit was observed...
Vacuum, 2017
This paper presents a thin nanocrystalline ZnO layer with embedded GaP nanowires (NWs). The NWs w... more This paper presents a thin nanocrystalline ZnO layer with embedded GaP nanowires (NWs). The NWs were grown in vapour-liquid-solid (VLS) mode by metal organic vapour phase epitaxy (MOVPE) at Au seeds formed from a very thin Au layer. The NWs were finally embedded in ZnO using deposition by RF sputtering combined with etching steps that resulted in a compact antireflection layer. We studied properties of such compact NWs structure by means of x-ray diffraction and atomic force microscopy. The study of mechanical properties was performed by nanoindentation measurements. The nanoindentation measurement showed that the incorporation of GaP nanowires into a ZnO layer led to increased hardness compared with that of a pure ZnO layer. The compact GaP NW/ZnO layer structure also exhibited some degree of pseudoelasticity. In addition, the mechanical properties of the compact nanowire layer are sufficiently robust to allow the thermo-compression bonding on the top of the structure.
Applied Surface Science, 2006
Composition, grading and doping of In 1ÀxÀy Al x Ga y P LED structures grown on the GaP substrate... more Composition, grading and doping of In 1ÀxÀy Al x Ga y P LED structures grown on the GaP substrate by step-wise graded In x Ga 1Àx P buffer were investigated by employing SIMS and SEM methods. Different amount of Al precursor has been used during MOCVD growth, resulting different Al content and correspondingly different wavelength of the emitted light. The buffer comprised of eight intentionally 300 nm thick In x Ga 1Àx P layers with step increase of In Dx In % 3% toward In 1ÀxÀy Al x Ga y P LED layers were grown to accommodate relatively high lattice mismatch between In 1ÀxÀy Al x Ga y P and GaP. Vertical structure of the samples has been visualised using backscattered electron method of the SEM. From the cleaved edge of samples the layers of different composition were revealed and the thickness of In 1ÀxÀy Al x Ga y P and In x Ga 1Àx P layers has been determined. In contrary p-n junction position was determined from SIMS depth profiling of the dopants and estimated only from secondary electron images. The compositional changes in the structures were examined using SIMS depth profiling, from which all the eight different In content steps in In x Ga 1Àx P buffer layers were detected. Composition of the LED layers has been determined from EDS measurements and compared with SIMS depth profiles. From SIMS and EDS measurements quaternary composition of the components Al, In, P and Ga were evaluated and optimized for the growth process. #
Applied Surface Science, 2010
Pairs of self-assembled InMnAs quantum dot structures and reference epitaxial layers (0 < x < 0.1... more Pairs of self-assembled InMnAs quantum dot structures and reference epitaxial layers (0 < x < 0.13) were prepared on GaAs substrates by low-pressure metal organic vapour phase epitaxy. Magnetic moment measurements indicated that reference epitaxial layer had a Curie temperature of 343 K independent on the composition. On the other hand, the quantum dots prepared under Stranski-Krastanov growth mode from the identical gas phase composition showed a lower value of Curie temperature. This value varied from 41 to 235 K in relation to the material composition. Moiré fringes at transmission electron microscopy plan view were used for characterization of strain in InMnAs quantum dot structures.
The spinodal-like decomposition of In x Ga 1Àx P epitaxial layer prepared by low-pressure metallo... more The spinodal-like decomposition of In x Ga 1Àx P epitaxial layer prepared by low-pressure metallorganic vapour phase epitaxy was studied by means of photoluminescence and transmission electron microscopy. Epitaxial layers were grown on GaP substrates at T g = 740 8C and reactor pressure of 20 mbar. We show that presence of spinodal-like decomposition occur at samples with InP mole fraction higher as x = 0.2 and V/III ratio of 75. The low-temperature photoluminescence spectra shows that in partially decomposed samples a characteristic broad band occurred close to 1.985 eV. An increase in the V/III ratio up to a value of 350 suppressed the decomposition, and PL signal with only one narrow transition was obtained. #
Physica Status Solidi (a), 2020
This work dealt with the preparation of twinned nanostructures for the optimization of substrates... more This work dealt with the preparation of twinned nanostructures for the optimization of substrates for SERS. At first GaP nanocones with hexagonal bases were prepared on GaP substrates by metal organic vapour phase epitaxy (MOVPE) at 650 °C. The substrates were then covered with Ag nanoparticles by RF sputtering. The Ag nanoparticles had very short inter–particle distances if they formed from thin Ag layers. The nominally 5 nm thick Ag layer resulted in the formation of an Ag nanoparticle assemblage with inter–particle distances shorter than 5 nm. The GaP nanocones and Ag nanoparticles worked in synergy to yield a substantial increase of SERS signal. This was verified with Rhodamine 6G molecules (at a concentration of 10-6M) at the typical Raman lines of 611 cm−1 and 773 cm−1. The enhancement of SERS was estimated to be as high as 106 for the nanocone substrate decorated with Ag nanoparticles from a nominally 5 nm thick Ag layer.
IEEE Transactions on Electron Devices
Vertical current conduction in a 1.3-<inline-formula> <tex-math notation="LaTeX&quo... more Vertical current conduction in a 1.3-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>-thick semi-insulating (SI) C-doped GaN grown on a GaN substrate is analyzed. During the growth, pressure was varied from 100 to 20 mbar in order to increase C concentration from <inline-formula> <tex-math notation="LaTeX">$\sim 1\times 10^{{17}}$ </tex-math></inline-formula> cm<sup>−3</sup> to <inline-formula> <tex-math notation="LaTeX">$\sim 6\times 10^{{18}}$ </tex-math></inline-formula> cm<sup>−3</sup>; SI GaN is sandwiched between two n-GaN layers. Optical transitions suggest two acceptor levels: ~0.9 eV above the valence band and ~0.6 eV below the conduction band. Current–voltage characterizations reveal a space-charge-limited-current conduction with an impact-ionization-assisted filling of traps in a moderately C-doped sample. On the other hand, highly compensated SI GaN forms a ~0.5-eV potential barrier at the interface with n-GaN, whereas the breakdown voltage exceeds 350 V. As the model explains, deep acceptors above the valence band compensate residual donors and lead to an electron mobility collapse. On the other hand, depending on C concentration, acceptors below the conduction band play a different role. In the moderately doped SI GaN, they act as electron traps and define the breakdown voltage. On the other hand, acceptors below the conduction band in highly compensated SI GaN are responsible for the barrier-controlled conduction and reaching of the avalanche.
Applied Surface Science
Abstract High resolution X-ray diffraction is commonly used for the analysis of single crystallin... more Abstract High resolution X-ray diffraction is commonly used for the analysis of single crystalline epitaxial layers exhibiting high degree of crystal perfection. The method enables to resolve fine variations of the measured intensities and therefore is very efficient in the investigation of the structural parameters of single or multilayered epitaxial systems. In this article the method combining the standard HR technique with grazing incidence set-up is outlined. It is shown that in non-coplanar geometry the intensity distribution within the section of reciprocal space perpendicular to the sample surface, standardly scanned in coplanar geometry, can be measured at constant angle of incidence α . For asymmetric diffractions that are not accessible in coplanar geometry the value of α can be decreased to extremely low values close to zero making the method depth-sensitive. The effect of non-coplanar geometry on the angular resolution is analyzed and the possible application of φ scans in asymmetric non-coplanar geometry is discussed. The proposed scans are illustrated by measurements on selected GaN based epitaxial layers and they can be applied also to other types of epitaxial systems with medium crystal quality.
Applied Surface Science
Abstract InAlN as a functional inorganic material is a promising alternative to the commonly used... more Abstract InAlN as a functional inorganic material is a promising alternative to the commonly used InGaN in tunnel diodes and optoelectronic devices, due to its tunable wider range of energy bandgap (0.65–6.2 eV), thus empowering utilization of the whole solar spectrum. Moreover, high electron drift velocity and carrier concentration are considered as the most desirable prerequisite of indium-rich InAlN. N-polar indium-rich InAlN could be more beneficial due to the reverse direction of the polarization compared to Ga-polar. However, unanswered questions persist concerning growth evolution of N-polar indium-rich InAlN grown by organometallic chemical vapor deposition (OMCVD). In this study, energy dispersive X-ray spectroscopy (EDX) and high-angle annular dark-field (HAADF) imaging are used to characterize N-polar I n 0.60 A l 0.40 N layer at nanometer scale in order to determine the evolution of the layer on (0001) sapphire substrate. Long nitridation of sapphire substrate leading to the formation of ~2 nm AlON ultrathin interlayer, which relaxes strain at the InAlN/sapphire interface with assistance of a low-temperature AlN interlayer is observed. EDX analysis confirms that after strain relaxation of InAlN layer, the indium-incorporation has only a weak dependence on the polarity of the layer. The incorporation of indium at preferential sites is also discussed at length.
Applied Surface Science
Abstract Zinc-doped gallium phosphide (GaP) nanowires and nanocones were grown by metal organic v... more Abstract Zinc-doped gallium phosphide (GaP) nanowires and nanocones were grown by metal organic vapour phase epitaxy (MOVPE) on GaP〈1 1 1〉B substrates by a VLS technique using 30 nm colloidal gold particles as seeds. The growth was performed in an AIX 200 MOVPE low-pressure reactor between 500 and 690 °C. As the growth temperature Tg was increased, GaP nanocrystals changed their shape from rod-like nanowires at 500 °C through tapered nanocones at between 610 and 660 °C and finally to biconical shape at 690 °C. The nanocones had hexagonal cross-sections at their bases following the orientation of the substrate. GaP substrates were nanostructured with nanowires or nanocones with the aim to create experimental platforms for further exploration namely for (1) the deposition of Ag nanoballs that should facilitate surface enhanced Raman scattering, and (2) the synthesis of a thin molybdenum disulphide (MoS2) layer that would be suitable for solar cell and water disinfection applications.
Applied Surface Science
Abstract The impact of oxidation agent and post-metallization annealing (PMA) on the quality of o... more Abstract The impact of oxidation agent and post-metallization annealing (PMA) on the quality of oxide-semiconductor interface in AlGaN/GaN metal-oxide semiconductor heterostructure field-effect transistors (MOS-HFETs) with HfO2 grown by atomic layer deposition (ALD) was investigated. About six orders of magnitude lower gate leakage current (∼10−7 mA/mm at −10 V) was observed for MOS-HFETs with HfO2 gate oxide grown by ALD using ozone oxidation agent (O-HfO2), compared with grown using water oxidation agent (T-HfO2). In addition, the output current frequency dispersion was effectively reduced for O-HfO2 by applying PMA performed at 400 °C in N2 ambient, where the current frequency dispersion measured using 100 ns-long pulses was reduced from 40% for as-deposited gate oxide to only 10% for devices after applied PMA. Frequency dispersion was found to be consistent with density of oxide/semiconductor interface states (Dit) determined near the semiconductor conduction and valence band edge using the capacitance-voltage curves measured at different temperatures (CV-T) and photo-assisted capacitance transient (photo-C-t) technique, respectively. MOS-HFET structures with O-HfO2 showed about one order of magnitude lower Dit near the semiconductor valence band compared with structures with T-HfO2 (2 × 1011 compared with 1012 eV−1 cm−2 at EC-E = 2.5 eV, respectively). Moreover, for devices with O-HfO2, Dit was further reduced in entire energy gap as a result of PMA performed at 400 °C. The increased Dit for T-HfO2 oxides was attributed to Hf-Hf bonds at the HfO2/GaN interface, as deduced X-ray photoelectron spectroscopy (XPS) analysis. In contrast, formation of Hf Hf bonds was negligible in as-deposited O-HfO2 oxide films, while PMA at 400 °C led to reduction of the hydroxyl group observed by XPS.
Indium Phosphide and Related Materials Conference, 2002
A modified wagon-wheel-mask technique was used to determine data for the reconstruction of a pola... more A modified wagon-wheel-mask technique was used to determine data for the reconstruction of a polar diagram of InP crystal wet etched in etchants based on HCl and H3PO4. It is demonstrated that the facet revelation and mask underetching within ±5° around [001] are very sensitive to the etchant composition as well as to mask orientation.
The Ninth International Conference on Advanced Semiconductor Devices and Mircosystems, 2012
ABSTRACT GaP/ZnO core-shell nanowires were prepared by Metal Organic Vapour Phase Epitaxy and RF ... more ABSTRACT GaP/ZnO core-shell nanowires were prepared by Metal Organic Vapour Phase Epitaxy and RF sputtering. We studied systematically room temperature photoluminescence of the NWs in the ultraviolet and green regions. Our study revealed that the UV peak position shifted slightly towards longer wavelengths while the green emission with the main transition at 2.25eV was almost unchanged.
Proceedings of 8th International Conference on Indium Phosphide and Related Materials
Currently, resonant cavity enhanced (RCE) photodetectors have received a great deal of attention ... more Currently, resonant cavity enhanced (RCE) photodetectors have received a great deal of attention for applications of photoreceivers with wavelength-selective capabilities and higher bandwith efficiency product. In the present work, we report on the design, growth and properties of RCE PIN photodiodes for 1300 nm wavelength region using In 0.52Al0.21Ga0.27As/InP bottom mirror overgrown by In0.53Ga0.47As/InP PIN photodiode
2008 International Conference on Advanced Semiconductor Devices and Microsystems, 2008
Extensive numerical experiments have shown that the iteratively reweighted 1 minimization algorit... more Extensive numerical experiments have shown that the iteratively reweighted 1 minimization algorithm (IRL1) is a very efficient method for variable selection, signal reconstruction and image processing. However no convergence results have been given for the IRL1. In this paper, we first give a global convergence theorem of the IRL1 for the 2p (0 < p < 1) minimization problem. We prove that any sequence generated by the IRL1 converges to a stationary point of the 2p minimization problem. Moreover, the stationary point is a global minimizer in certain domain and the convergence rate is approximately linear under certain conditions. We derive posteriori error bounds which can be used to construct practical stopping rules for the algorithm. Other contribution of this paper is to prove the uniqueness of solution of the truncated p minimization problem under the truncated null space property which is weaker than the restricted isometry property.
The Ninth International Conference on Advanced Semiconductor Devices and Mircosystems, 2012
ABSTRACT We have studied the properties of the prepared ZnO thin films on GaP nanowires deposited... more ABSTRACT We have studied the properties of the prepared ZnO thin films on GaP nanowires deposited by reactive magnetron sputtering at different target-substrate geometry and deposition conditions. ZnO/GaP-NW core-shell structures were created on MOCVD-GaP NWs grown on Zn-doped GaP(111)B substrates. Some important physical properties of the ZnO films and core-shell GaP/ZnO heterojunctions were investigated.
Applied Surface Science, 2017
Indium nitride (InN) is a very promising direct bandgap semiconductor material for near-infrared ... more Indium nitride (InN) is a very promising direct bandgap semiconductor material for near-infrared optoelectronic devices and high speed transistors, however InN growth is much more challenging compared to other III-N semiconductors. In this study we analysed the impact of pre-growth vicinal c-plane sapphire substrate nitridation on the electrical, optical, and strucutral properties of N-polar InN/InAlN heterostructures and the InN crystal habit. While a short cool-down nitridation phase resulted in a high quality InAlN layer and low quality InN layer, it was the opposite for a long cool-down nitridation phase. A trade-off between the electrical and optical properties was observed: the short nitridation cool-down produced InN layers with a higher electron mobility of 629 cm2 V−1 s−1 and low photoluminescence (PL) emission, and the long one resulted in InN with a ∼21% lower electron mobility of 497 cm2 V−1s−1 but strong PL emission. Also, a very different InN crystal habit was observed...
Vacuum, 2017
This paper presents a thin nanocrystalline ZnO layer with embedded GaP nanowires (NWs). The NWs w... more This paper presents a thin nanocrystalline ZnO layer with embedded GaP nanowires (NWs). The NWs were grown in vapour-liquid-solid (VLS) mode by metal organic vapour phase epitaxy (MOVPE) at Au seeds formed from a very thin Au layer. The NWs were finally embedded in ZnO using deposition by RF sputtering combined with etching steps that resulted in a compact antireflection layer. We studied properties of such compact NWs structure by means of x-ray diffraction and atomic force microscopy. The study of mechanical properties was performed by nanoindentation measurements. The nanoindentation measurement showed that the incorporation of GaP nanowires into a ZnO layer led to increased hardness compared with that of a pure ZnO layer. The compact GaP NW/ZnO layer structure also exhibited some degree of pseudoelasticity. In addition, the mechanical properties of the compact nanowire layer are sufficiently robust to allow the thermo-compression bonding on the top of the structure.
Applied Surface Science, 2006
Composition, grading and doping of In 1ÀxÀy Al x Ga y P LED structures grown on the GaP substrate... more Composition, grading and doping of In 1ÀxÀy Al x Ga y P LED structures grown on the GaP substrate by step-wise graded In x Ga 1Àx P buffer were investigated by employing SIMS and SEM methods. Different amount of Al precursor has been used during MOCVD growth, resulting different Al content and correspondingly different wavelength of the emitted light. The buffer comprised of eight intentionally 300 nm thick In x Ga 1Àx P layers with step increase of In Dx In % 3% toward In 1ÀxÀy Al x Ga y P LED layers were grown to accommodate relatively high lattice mismatch between In 1ÀxÀy Al x Ga y P and GaP. Vertical structure of the samples has been visualised using backscattered electron method of the SEM. From the cleaved edge of samples the layers of different composition were revealed and the thickness of In 1ÀxÀy Al x Ga y P and In x Ga 1Àx P layers has been determined. In contrary p-n junction position was determined from SIMS depth profiling of the dopants and estimated only from secondary electron images. The compositional changes in the structures were examined using SIMS depth profiling, from which all the eight different In content steps in In x Ga 1Àx P buffer layers were detected. Composition of the LED layers has been determined from EDS measurements and compared with SIMS depth profiles. From SIMS and EDS measurements quaternary composition of the components Al, In, P and Ga were evaluated and optimized for the growth process. #
Applied Surface Science, 2010
Pairs of self-assembled InMnAs quantum dot structures and reference epitaxial layers (0 < x < 0.1... more Pairs of self-assembled InMnAs quantum dot structures and reference epitaxial layers (0 < x < 0.13) were prepared on GaAs substrates by low-pressure metal organic vapour phase epitaxy. Magnetic moment measurements indicated that reference epitaxial layer had a Curie temperature of 343 K independent on the composition. On the other hand, the quantum dots prepared under Stranski-Krastanov growth mode from the identical gas phase composition showed a lower value of Curie temperature. This value varied from 41 to 235 K in relation to the material composition. Moiré fringes at transmission electron microscopy plan view were used for characterization of strain in InMnAs quantum dot structures.
The spinodal-like decomposition of In x Ga 1Àx P epitaxial layer prepared by low-pressure metallo... more The spinodal-like decomposition of In x Ga 1Àx P epitaxial layer prepared by low-pressure metallorganic vapour phase epitaxy was studied by means of photoluminescence and transmission electron microscopy. Epitaxial layers were grown on GaP substrates at T g = 740 8C and reactor pressure of 20 mbar. We show that presence of spinodal-like decomposition occur at samples with InP mole fraction higher as x = 0.2 and V/III ratio of 75. The low-temperature photoluminescence spectra shows that in partially decomposed samples a characteristic broad band occurred close to 1.985 eV. An increase in the V/III ratio up to a value of 350 suppressed the decomposition, and PL signal with only one narrow transition was obtained. #
Physica Status Solidi (a), 2020
This work dealt with the preparation of twinned nanostructures for the optimization of substrates... more This work dealt with the preparation of twinned nanostructures for the optimization of substrates for SERS. At first GaP nanocones with hexagonal bases were prepared on GaP substrates by metal organic vapour phase epitaxy (MOVPE) at 650 °C. The substrates were then covered with Ag nanoparticles by RF sputtering. The Ag nanoparticles had very short inter–particle distances if they formed from thin Ag layers. The nominally 5 nm thick Ag layer resulted in the formation of an Ag nanoparticle assemblage with inter–particle distances shorter than 5 nm. The GaP nanocones and Ag nanoparticles worked in synergy to yield a substantial increase of SERS signal. This was verified with Rhodamine 6G molecules (at a concentration of 10-6M) at the typical Raman lines of 611 cm−1 and 773 cm−1. The enhancement of SERS was estimated to be as high as 106 for the nanocone substrate decorated with Ag nanoparticles from a nominally 5 nm thick Ag layer.
IEEE Transactions on Electron Devices
Vertical current conduction in a 1.3-<inline-formula> <tex-math notation="LaTeX&quo... more Vertical current conduction in a 1.3-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>-thick semi-insulating (SI) C-doped GaN grown on a GaN substrate is analyzed. During the growth, pressure was varied from 100 to 20 mbar in order to increase C concentration from <inline-formula> <tex-math notation="LaTeX">$\sim 1\times 10^{{17}}$ </tex-math></inline-formula> cm<sup>−3</sup> to <inline-formula> <tex-math notation="LaTeX">$\sim 6\times 10^{{18}}$ </tex-math></inline-formula> cm<sup>−3</sup>; SI GaN is sandwiched between two n-GaN layers. Optical transitions suggest two acceptor levels: ~0.9 eV above the valence band and ~0.6 eV below the conduction band. Current–voltage characterizations reveal a space-charge-limited-current conduction with an impact-ionization-assisted filling of traps in a moderately C-doped sample. On the other hand, highly compensated SI GaN forms a ~0.5-eV potential barrier at the interface with n-GaN, whereas the breakdown voltage exceeds 350 V. As the model explains, deep acceptors above the valence band compensate residual donors and lead to an electron mobility collapse. On the other hand, depending on C concentration, acceptors below the conduction band play a different role. In the moderately doped SI GaN, they act as electron traps and define the breakdown voltage. On the other hand, acceptors below the conduction band in highly compensated SI GaN are responsible for the barrier-controlled conduction and reaching of the avalanche.
Applied Surface Science
Abstract High resolution X-ray diffraction is commonly used for the analysis of single crystallin... more Abstract High resolution X-ray diffraction is commonly used for the analysis of single crystalline epitaxial layers exhibiting high degree of crystal perfection. The method enables to resolve fine variations of the measured intensities and therefore is very efficient in the investigation of the structural parameters of single or multilayered epitaxial systems. In this article the method combining the standard HR technique with grazing incidence set-up is outlined. It is shown that in non-coplanar geometry the intensity distribution within the section of reciprocal space perpendicular to the sample surface, standardly scanned in coplanar geometry, can be measured at constant angle of incidence α . For asymmetric diffractions that are not accessible in coplanar geometry the value of α can be decreased to extremely low values close to zero making the method depth-sensitive. The effect of non-coplanar geometry on the angular resolution is analyzed and the possible application of φ scans in asymmetric non-coplanar geometry is discussed. The proposed scans are illustrated by measurements on selected GaN based epitaxial layers and they can be applied also to other types of epitaxial systems with medium crystal quality.
Applied Surface Science
Abstract InAlN as a functional inorganic material is a promising alternative to the commonly used... more Abstract InAlN as a functional inorganic material is a promising alternative to the commonly used InGaN in tunnel diodes and optoelectronic devices, due to its tunable wider range of energy bandgap (0.65–6.2 eV), thus empowering utilization of the whole solar spectrum. Moreover, high electron drift velocity and carrier concentration are considered as the most desirable prerequisite of indium-rich InAlN. N-polar indium-rich InAlN could be more beneficial due to the reverse direction of the polarization compared to Ga-polar. However, unanswered questions persist concerning growth evolution of N-polar indium-rich InAlN grown by organometallic chemical vapor deposition (OMCVD). In this study, energy dispersive X-ray spectroscopy (EDX) and high-angle annular dark-field (HAADF) imaging are used to characterize N-polar I n 0.60 A l 0.40 N layer at nanometer scale in order to determine the evolution of the layer on (0001) sapphire substrate. Long nitridation of sapphire substrate leading to the formation of ~2 nm AlON ultrathin interlayer, which relaxes strain at the InAlN/sapphire interface with assistance of a low-temperature AlN interlayer is observed. EDX analysis confirms that after strain relaxation of InAlN layer, the indium-incorporation has only a weak dependence on the polarity of the layer. The incorporation of indium at preferential sites is also discussed at length.
Applied Surface Science
Abstract Zinc-doped gallium phosphide (GaP) nanowires and nanocones were grown by metal organic v... more Abstract Zinc-doped gallium phosphide (GaP) nanowires and nanocones were grown by metal organic vapour phase epitaxy (MOVPE) on GaP〈1 1 1〉B substrates by a VLS technique using 30 nm colloidal gold particles as seeds. The growth was performed in an AIX 200 MOVPE low-pressure reactor between 500 and 690 °C. As the growth temperature Tg was increased, GaP nanocrystals changed their shape from rod-like nanowires at 500 °C through tapered nanocones at between 610 and 660 °C and finally to biconical shape at 690 °C. The nanocones had hexagonal cross-sections at their bases following the orientation of the substrate. GaP substrates were nanostructured with nanowires or nanocones with the aim to create experimental platforms for further exploration namely for (1) the deposition of Ag nanoballs that should facilitate surface enhanced Raman scattering, and (2) the synthesis of a thin molybdenum disulphide (MoS2) layer that would be suitable for solar cell and water disinfection applications.
Applied Surface Science
Abstract The impact of oxidation agent and post-metallization annealing (PMA) on the quality of o... more Abstract The impact of oxidation agent and post-metallization annealing (PMA) on the quality of oxide-semiconductor interface in AlGaN/GaN metal-oxide semiconductor heterostructure field-effect transistors (MOS-HFETs) with HfO2 grown by atomic layer deposition (ALD) was investigated. About six orders of magnitude lower gate leakage current (∼10−7 mA/mm at −10 V) was observed for MOS-HFETs with HfO2 gate oxide grown by ALD using ozone oxidation agent (O-HfO2), compared with grown using water oxidation agent (T-HfO2). In addition, the output current frequency dispersion was effectively reduced for O-HfO2 by applying PMA performed at 400 °C in N2 ambient, where the current frequency dispersion measured using 100 ns-long pulses was reduced from 40% for as-deposited gate oxide to only 10% for devices after applied PMA. Frequency dispersion was found to be consistent with density of oxide/semiconductor interface states (Dit) determined near the semiconductor conduction and valence band edge using the capacitance-voltage curves measured at different temperatures (CV-T) and photo-assisted capacitance transient (photo-C-t) technique, respectively. MOS-HFET structures with O-HfO2 showed about one order of magnitude lower Dit near the semiconductor valence band compared with structures with T-HfO2 (2 × 1011 compared with 1012 eV−1 cm−2 at EC-E = 2.5 eV, respectively). Moreover, for devices with O-HfO2, Dit was further reduced in entire energy gap as a result of PMA performed at 400 °C. The increased Dit for T-HfO2 oxides was attributed to Hf-Hf bonds at the HfO2/GaN interface, as deduced X-ray photoelectron spectroscopy (XPS) analysis. In contrast, formation of Hf Hf bonds was negligible in as-deposited O-HfO2 oxide films, while PMA at 400 °C led to reduction of the hydroxyl group observed by XPS.