2017 42nd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2017
The bow-tie (BT) diodes with broken symmetry for room temperature terahertz detection were develo... more The bow-tie (BT) diodes with broken symmetry for room temperature terahertz detection were developed of AlGaN/GaN high electron mobility transistor (HEMT) structures with two dimensional electron gas (2DEG). The performance of new THz detectors was obtained at 0.3 THz frequency and compared with the most sensitive InGaAs-based BT diodes of the same design. Our experiments at sub-THz frequency revealed the potential of the AlGaN/GaN HEMT-based BT diodes as sensitive and reliable room temperature THz sensors.
The single crystals of GaN grown at high hydrostatic pressures (about 15 kbar) and high temperatu... more The single crystals of GaN grown at high hydrostatic pressures (about 15 kbar) and high temperatures (about 1800K) possess a very low dislocation density (below 10 3 cm ) and sizes of about 100 mm 2 . These crystals are used as substrates for MOVPE growth of laser structures. The most important question we had to answer was if the ternary compounds InGaN and AlGaN layers on GaN would be strained or relaxed by misfit dislocations. To answer this question we grew a series of these ternary layers of various compositions and thickness and examined them using high−resolution X−ray diffraction sensitive to dislocation density larger then 10 4 cm−2. These experimental results indicated that the laser structure grown on bulk GaN crystal should be fully strained (without mismatch dislocations). The further research confirmed this prediction. Atomic force microscopy (AFM) scans do not show any threading dislocations. The perfect atomic steps are not disturbed by the presence of dislocations a...
2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2018
We report on comparison studies between a novel transistor like device and two dimensional Fin Fi... more We report on comparison studies between a novel transistor like device and two dimensional Fin Field-Effect transistor towards their applications in a terahertz resonant detector. Both device structures have been fabricated on the same wafer of GaN/AIGaN epistructure during one processing run. The proposed here the transistor-like structure has two side Schottky gates, which can be biased towards complete pinch-off the 2DEG channel in this device. At certain conditions, near to pinch-off region, it is possible to obtain one dimensional current flow. This feature is especially attractive for THz resonant detector approach, which will be discussed in details.
2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), 2021
We report THz induced ratchet photocurrent in AlGaN/GaN heterostructures superimposed with asymme... more We report THz induced ratchet photocurrent in AlGaN/GaN heterostructures superimposed with asymmetric dual-grating gate structure. The photocurrent shows giant magneto-oscillations in the regime of high magnetic fields. Peculiarly, the envelope of these oscillations exhibits large beatings as a function of the magnetic field. We demonstrate experimentally and theoretically that the beatings are caused by the spin-orbit interaction in GaN conduction band. Our results show how THz photoconductivity can be used for studies of spin dependent effects in GaN-based materials.
ESSDERC 2019 - 49th European Solid-State Device Research Conference (ESSDERC), 2019
GaN/AlGaN lateral Schottky diodes, FinFETs and EdgeFETs were fabricated and studied. All these de... more GaN/AlGaN lateral Schottky diodes, FinFETs and EdgeFETs were fabricated and studied. All these devices have fin-shaped active area, characterized by small input capacitance and are promising for high frequency applications.
Materials Science in Semiconductor Processing, 2019
AlGaN/GaN heterostructures were grown on "on-axis" and 2° off (0001) 4H-SiC substrates by metalor... more AlGaN/GaN heterostructures were grown on "on-axis" and 2° off (0001) 4H-SiC substrates by metalorganic vapor phase epitaxy (MOVPE). Structural characterization was performed by transmission electron microscopy. The dislocation density, being greater in the on-axis case, is gradually reduced in the GaN layer and is forming dislocation loops in the lower region. Steps aligned along [11 ̅ 00] in the off-axis case give rise to simultaneous defect formation. In the onaxis case, an almost zero density of steps is observed, with the main origin of defects probably being the orientation mismatch at the grain boundaries between the small not fully coalesced AlN grains. V-shaped formations are observed in the AlN nucleation layer, but are more frequent in the off-axis case, probably enhanced by the presence of steps. These V-shaped formations are completely overgrown by the GaN layer, during the subsequent deposition, presenting AlGaN areas in the walls of the defect, indicating an inter-diffusion between the layers. Finally, at the AlGaN/GaN heterostructure surface in the on-axis case, V-shapes are observed, with the AlGaN (21% Al) thickness exceeding the critical for relaxation thickness. On the other hand, no relaxation in the form of V-shape creation is observed in the off-axis case, probably due to the smaller AlGaN thickness (less than 21% Al). The AlN spacer layer, grown in between the heterostructure, presents a uniform thickness and clear interfaces.
ABSTRACT The work shows structural changes of GaN layers on sapphire induced by annealing at temp... more ABSTRACT The work shows structural changes of GaN layers on sapphire induced by annealing at temperatures up to 1550 degrees C. Such high temperatures could be used due to the application of high nitrogen pressure of up to 16.5 kbar (at 1 bar, GaN decomposes at about 1000 degrees C). After the annealing, the layers were examined using high-resolution X-ray diffraction. It was observed that the annealing at temperatures above 1250 degrees C causes the following changes in the microstructure of the GaN layers on sapphire: (i) a decrease of the out-of-plane tilt mosaicity (X-ray rocking curves of symmetrical reflections become narrower), (ii) an increase of the in-plane twist mosaicity (rocking curves of asymmetrical reflections become broader), (iii) an increase of the thermal strain (the perpendicular lattice parameters increase, the inplane lattice parameters decrease). The increase of the strain is accompanied by the blue shift of the photoluminescence excitonic peaks. The magnitudes of the changes observed were inversely proportional to the initial tilt mosaicity of the layers.
Crack free GaInN/AlInN multiple quantum wells were grown by rf plasma-assisted molecular beam epi... more Crack free GaInN/AlInN multiple quantum wells were grown by rf plasma-assisted molecular beam epitaxy on (0001) GaN/sapphire substrates. The strain-engineering concept was applied to eliminate cracking effect for growth of intersubband structures on GaN. Indium contained ternary compounds of barrier and well layers are contrary strained to the substrate material. A series of crack free GaInN/AlInN intersubband structures on (0001) GaN was fabricated and investigated. The assumed composition and layered structure were confirmed by room temperature photoluminescence and X-ray diffraction measurements. The intersubband measurements were done in multipass waveguide geometry by applying direct intersubband absorption and photoinduced intersubband absorption measurements. The optimized structure design contains forty periods of Si-doped GaInN/AlInN quantum wells and exhibits strong intersubband absorption.
We report Schottky diodes (SDs) and High Electron Mobility Transistors (HEMTs) fabricated of 2DEG... more We report Schottky diodes (SDs) and High Electron Mobility Transistors (HEMTs) fabricated of 2DEG AlGaN/GaN structures grown by Metalorganic Chemical Vapour Phase Epitaxy (MOVPE) on sapphire substrate. The SDs and HEMTs were designed intentionally without surface passivation and were successfully fabricated at the Center for Physical Sciences and Technology (CPST), using standard UV photolithography procedures. The performance of Ohmic contacts formed of quaternary Ti/Al/Ni/Au stack was optimized varying the temperature of rapid thermal annealing process. Deposited on the semiconductor metal Ni/Au stack was used to form 0.75 eV height Schottky barriers. The fabricated SDs demonstrated low reverse current and high electric current switching ratio while the HEMTs showed high transconductance and drain saturation currents performance with good transistor channel closing. This work paves a way to develop advanced AlGaN/GaN based HEMT structures as well as new electronic components for operation at high powers and high frequencies.
Series of ten-, twenty-, and thirty-period (Al,Ga)N-based distributed Bragg reflectors (DBR) have... more Series of ten-, twenty-, and thirty-period (Al,Ga)N-based distributed Bragg reflectors (DBR) have been grown by low-pressure metalorganic vapour phase epitaxy on bulk GaN substrates. Respective mirror target wavelength reflectances of 54, 72, and 86%, as well as stop band-widths lie in nearly exact agreement with the simulations. The DBR are found to be crack-free if pseudomorphically grown on partially relaxed (Ga,In)N compliance layers. In a second series GaN lambda-cavities are introduced into the mirror structures forming nominally symmetric Fabry-Perot resonators sandwiched either between the air/GaNinterface and an underlying Al x Ga 1-x N/GaN-Bragg mirror, or sandwiched between a top-and a bottom-DBR with various numbers of Al x Ga 1-x N/GaN quarter-wave layers. Measured reflectance spectra of samples without top-DBR agree well with the simulations, whereas reflectance spectra of samples with top-DBR remain significantly below the simulations. Upon introduction of Al x Ga 1-x N/GaN-based bottom-DBR with 90% target wavelength reflectance up to 15.5% light extraction are predicted for encapsulated light emitting diodes.
We present transport properties of AlGaN/GaN heterostructures grown over high-pressure bulk GaN s... more We present transport properties of AlGaN/GaN heterostructures grown over high-pressure bulk GaN substrates. The experimental results include the conductivity tensor measurements in a magnetic field up to 23 T in a wide temperature range 2 K-300 K for Hall bar samples. The room temperature high field data allow us to clearly separate contributions of a parasitic parallel conduction from 2DEG conduction in all investigated heterostructures. The room temperature mobility limit for 2D electrons in GaN/AlGaN heterojunctions grown on defect free GaN bulk substrates is around 2400 cm 2 /Vs. The Quantum Hall Effect studies are performed in the magnetic fields up to 23 T and temperatures between 1.6 K and 15 K This high magnetic field in combination with very high mobility (over 60000 cm 2 /Vs) in the sample grown on the bulk GaN substrate allow us to determine the activation energy in cyclotron gap from longitudinal magnetoresistance.
... Access to the website will be disrupted as follows: New York 0630 EDT to 0830 EDT; London 113... more ... Access to the website will be disrupted as follows: New York 0630 EDT to 0830 EDT; London 1130 GMT to 1330 GMT; Singapore 1930 SGT to 2130 SGT. ... Original Paper. Doping of Homoepitaxial GaN Layers. P. Prystawko 1 ,; M. Leszczynski 1 ,; B. Beaumont 2 ,; P. Gibart 2 ,; ...
We present results of temperature-dependent, time-resolved photoluminescence (PL) measurements on... more We present results of temperature-dependent, time-resolved photoluminescence (PL) measurements on a set of Ga1−xInxN (x≅0.08) layers grown at the same conditions on three different substrates: bulk (high pressure grown) GaN, SiC and Al2O3. At 9 K, the maximum of the PL occurs at about 3.1 eV. The linewidths are 48, 80 and 90 meV for the layers grown on GaN,
ABSTRACT GaN layers grown by metalorganic vapor phase epitaxy on sapphire substrates in epitaxial... more ABSTRACT GaN layers grown by metalorganic vapor phase epitaxy on sapphire substrates in epitaxial lateral overgrowth (ELOG) mode were studied using the high-resolution X-ray diffraction technique in double and triple axis modes (including reciprocal lattice mapping), both in reflection and transmission geometries. GaN layer grown on unmasked sapphire was examined in the same way for a comparison. We have found that in the fully overgrown ELOG structures: (i) hexagonal unit cells are deformed, so the lattice parameters a⊥ (perpendicular to the stripes) and a30 (inclined by 30° to the stripes) are smaller by up to 0.1% and 0.02%, respectively, as compared to those in the GaN buffer, (ii) curvature radii of the samples are of 1.2–1.4 m in the direction parallel to the stripes and of 1 m in the direction perpendicular to the stripes, which is consistent with the strain observed, and (iii) sapphire miscut along the 〈11.0〉 direction (i.e. perpendicular to the stripes) causes an additional inclination of ELOG lattice planes with respect to those in the buffer. A qualitative explanation of these findings is presented taking into account increase of GaN grain size in the ELOG layers.
2017 42nd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2017
The bow-tie (BT) diodes with broken symmetry for room temperature terahertz detection were develo... more The bow-tie (BT) diodes with broken symmetry for room temperature terahertz detection were developed of AlGaN/GaN high electron mobility transistor (HEMT) structures with two dimensional electron gas (2DEG). The performance of new THz detectors was obtained at 0.3 THz frequency and compared with the most sensitive InGaAs-based BT diodes of the same design. Our experiments at sub-THz frequency revealed the potential of the AlGaN/GaN HEMT-based BT diodes as sensitive and reliable room temperature THz sensors.
The single crystals of GaN grown at high hydrostatic pressures (about 15 kbar) and high temperatu... more The single crystals of GaN grown at high hydrostatic pressures (about 15 kbar) and high temperatures (about 1800K) possess a very low dislocation density (below 10 3 cm ) and sizes of about 100 mm 2 . These crystals are used as substrates for MOVPE growth of laser structures. The most important question we had to answer was if the ternary compounds InGaN and AlGaN layers on GaN would be strained or relaxed by misfit dislocations. To answer this question we grew a series of these ternary layers of various compositions and thickness and examined them using high−resolution X−ray diffraction sensitive to dislocation density larger then 10 4 cm−2. These experimental results indicated that the laser structure grown on bulk GaN crystal should be fully strained (without mismatch dislocations). The further research confirmed this prediction. Atomic force microscopy (AFM) scans do not show any threading dislocations. The perfect atomic steps are not disturbed by the presence of dislocations a...
2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2018
We report on comparison studies between a novel transistor like device and two dimensional Fin Fi... more We report on comparison studies between a novel transistor like device and two dimensional Fin Field-Effect transistor towards their applications in a terahertz resonant detector. Both device structures have been fabricated on the same wafer of GaN/AIGaN epistructure during one processing run. The proposed here the transistor-like structure has two side Schottky gates, which can be biased towards complete pinch-off the 2DEG channel in this device. At certain conditions, near to pinch-off region, it is possible to obtain one dimensional current flow. This feature is especially attractive for THz resonant detector approach, which will be discussed in details.
2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), 2021
We report THz induced ratchet photocurrent in AlGaN/GaN heterostructures superimposed with asymme... more We report THz induced ratchet photocurrent in AlGaN/GaN heterostructures superimposed with asymmetric dual-grating gate structure. The photocurrent shows giant magneto-oscillations in the regime of high magnetic fields. Peculiarly, the envelope of these oscillations exhibits large beatings as a function of the magnetic field. We demonstrate experimentally and theoretically that the beatings are caused by the spin-orbit interaction in GaN conduction band. Our results show how THz photoconductivity can be used for studies of spin dependent effects in GaN-based materials.
ESSDERC 2019 - 49th European Solid-State Device Research Conference (ESSDERC), 2019
GaN/AlGaN lateral Schottky diodes, FinFETs and EdgeFETs were fabricated and studied. All these de... more GaN/AlGaN lateral Schottky diodes, FinFETs and EdgeFETs were fabricated and studied. All these devices have fin-shaped active area, characterized by small input capacitance and are promising for high frequency applications.
Materials Science in Semiconductor Processing, 2019
AlGaN/GaN heterostructures were grown on "on-axis" and 2° off (0001) 4H-SiC substrates by metalor... more AlGaN/GaN heterostructures were grown on "on-axis" and 2° off (0001) 4H-SiC substrates by metalorganic vapor phase epitaxy (MOVPE). Structural characterization was performed by transmission electron microscopy. The dislocation density, being greater in the on-axis case, is gradually reduced in the GaN layer and is forming dislocation loops in the lower region. Steps aligned along [11 ̅ 00] in the off-axis case give rise to simultaneous defect formation. In the onaxis case, an almost zero density of steps is observed, with the main origin of defects probably being the orientation mismatch at the grain boundaries between the small not fully coalesced AlN grains. V-shaped formations are observed in the AlN nucleation layer, but are more frequent in the off-axis case, probably enhanced by the presence of steps. These V-shaped formations are completely overgrown by the GaN layer, during the subsequent deposition, presenting AlGaN areas in the walls of the defect, indicating an inter-diffusion between the layers. Finally, at the AlGaN/GaN heterostructure surface in the on-axis case, V-shapes are observed, with the AlGaN (21% Al) thickness exceeding the critical for relaxation thickness. On the other hand, no relaxation in the form of V-shape creation is observed in the off-axis case, probably due to the smaller AlGaN thickness (less than 21% Al). The AlN spacer layer, grown in between the heterostructure, presents a uniform thickness and clear interfaces.
ABSTRACT The work shows structural changes of GaN layers on sapphire induced by annealing at temp... more ABSTRACT The work shows structural changes of GaN layers on sapphire induced by annealing at temperatures up to 1550 degrees C. Such high temperatures could be used due to the application of high nitrogen pressure of up to 16.5 kbar (at 1 bar, GaN decomposes at about 1000 degrees C). After the annealing, the layers were examined using high-resolution X-ray diffraction. It was observed that the annealing at temperatures above 1250 degrees C causes the following changes in the microstructure of the GaN layers on sapphire: (i) a decrease of the out-of-plane tilt mosaicity (X-ray rocking curves of symmetrical reflections become narrower), (ii) an increase of the in-plane twist mosaicity (rocking curves of asymmetrical reflections become broader), (iii) an increase of the thermal strain (the perpendicular lattice parameters increase, the inplane lattice parameters decrease). The increase of the strain is accompanied by the blue shift of the photoluminescence excitonic peaks. The magnitudes of the changes observed were inversely proportional to the initial tilt mosaicity of the layers.
Crack free GaInN/AlInN multiple quantum wells were grown by rf plasma-assisted molecular beam epi... more Crack free GaInN/AlInN multiple quantum wells were grown by rf plasma-assisted molecular beam epitaxy on (0001) GaN/sapphire substrates. The strain-engineering concept was applied to eliminate cracking effect for growth of intersubband structures on GaN. Indium contained ternary compounds of barrier and well layers are contrary strained to the substrate material. A series of crack free GaInN/AlInN intersubband structures on (0001) GaN was fabricated and investigated. The assumed composition and layered structure were confirmed by room temperature photoluminescence and X-ray diffraction measurements. The intersubband measurements were done in multipass waveguide geometry by applying direct intersubband absorption and photoinduced intersubband absorption measurements. The optimized structure design contains forty periods of Si-doped GaInN/AlInN quantum wells and exhibits strong intersubband absorption.
We report Schottky diodes (SDs) and High Electron Mobility Transistors (HEMTs) fabricated of 2DEG... more We report Schottky diodes (SDs) and High Electron Mobility Transistors (HEMTs) fabricated of 2DEG AlGaN/GaN structures grown by Metalorganic Chemical Vapour Phase Epitaxy (MOVPE) on sapphire substrate. The SDs and HEMTs were designed intentionally without surface passivation and were successfully fabricated at the Center for Physical Sciences and Technology (CPST), using standard UV photolithography procedures. The performance of Ohmic contacts formed of quaternary Ti/Al/Ni/Au stack was optimized varying the temperature of rapid thermal annealing process. Deposited on the semiconductor metal Ni/Au stack was used to form 0.75 eV height Schottky barriers. The fabricated SDs demonstrated low reverse current and high electric current switching ratio while the HEMTs showed high transconductance and drain saturation currents performance with good transistor channel closing. This work paves a way to develop advanced AlGaN/GaN based HEMT structures as well as new electronic components for operation at high powers and high frequencies.
Series of ten-, twenty-, and thirty-period (Al,Ga)N-based distributed Bragg reflectors (DBR) have... more Series of ten-, twenty-, and thirty-period (Al,Ga)N-based distributed Bragg reflectors (DBR) have been grown by low-pressure metalorganic vapour phase epitaxy on bulk GaN substrates. Respective mirror target wavelength reflectances of 54, 72, and 86%, as well as stop band-widths lie in nearly exact agreement with the simulations. The DBR are found to be crack-free if pseudomorphically grown on partially relaxed (Ga,In)N compliance layers. In a second series GaN lambda-cavities are introduced into the mirror structures forming nominally symmetric Fabry-Perot resonators sandwiched either between the air/GaNinterface and an underlying Al x Ga 1-x N/GaN-Bragg mirror, or sandwiched between a top-and a bottom-DBR with various numbers of Al x Ga 1-x N/GaN quarter-wave layers. Measured reflectance spectra of samples without top-DBR agree well with the simulations, whereas reflectance spectra of samples with top-DBR remain significantly below the simulations. Upon introduction of Al x Ga 1-x N/GaN-based bottom-DBR with 90% target wavelength reflectance up to 15.5% light extraction are predicted for encapsulated light emitting diodes.
We present transport properties of AlGaN/GaN heterostructures grown over high-pressure bulk GaN s... more We present transport properties of AlGaN/GaN heterostructures grown over high-pressure bulk GaN substrates. The experimental results include the conductivity tensor measurements in a magnetic field up to 23 T in a wide temperature range 2 K-300 K for Hall bar samples. The room temperature high field data allow us to clearly separate contributions of a parasitic parallel conduction from 2DEG conduction in all investigated heterostructures. The room temperature mobility limit for 2D electrons in GaN/AlGaN heterojunctions grown on defect free GaN bulk substrates is around 2400 cm 2 /Vs. The Quantum Hall Effect studies are performed in the magnetic fields up to 23 T and temperatures between 1.6 K and 15 K This high magnetic field in combination with very high mobility (over 60000 cm 2 /Vs) in the sample grown on the bulk GaN substrate allow us to determine the activation energy in cyclotron gap from longitudinal magnetoresistance.
... Access to the website will be disrupted as follows: New York 0630 EDT to 0830 EDT; London 113... more ... Access to the website will be disrupted as follows: New York 0630 EDT to 0830 EDT; London 1130 GMT to 1330 GMT; Singapore 1930 SGT to 2130 SGT. ... Original Paper. Doping of Homoepitaxial GaN Layers. P. Prystawko 1 ,; M. Leszczynski 1 ,; B. Beaumont 2 ,; P. Gibart 2 ,; ...
We present results of temperature-dependent, time-resolved photoluminescence (PL) measurements on... more We present results of temperature-dependent, time-resolved photoluminescence (PL) measurements on a set of Ga1−xInxN (x≅0.08) layers grown at the same conditions on three different substrates: bulk (high pressure grown) GaN, SiC and Al2O3. At 9 K, the maximum of the PL occurs at about 3.1 eV. The linewidths are 48, 80 and 90 meV for the layers grown on GaN,
ABSTRACT GaN layers grown by metalorganic vapor phase epitaxy on sapphire substrates in epitaxial... more ABSTRACT GaN layers grown by metalorganic vapor phase epitaxy on sapphire substrates in epitaxial lateral overgrowth (ELOG) mode were studied using the high-resolution X-ray diffraction technique in double and triple axis modes (including reciprocal lattice mapping), both in reflection and transmission geometries. GaN layer grown on unmasked sapphire was examined in the same way for a comparison. We have found that in the fully overgrown ELOG structures: (i) hexagonal unit cells are deformed, so the lattice parameters a⊥ (perpendicular to the stripes) and a30 (inclined by 30° to the stripes) are smaller by up to 0.1% and 0.02%, respectively, as compared to those in the GaN buffer, (ii) curvature radii of the samples are of 1.2–1.4 m in the direction parallel to the stripes and of 1 m in the direction perpendicular to the stripes, which is consistent with the strain observed, and (iii) sapphire miscut along the 〈11.0〉 direction (i.e. perpendicular to the stripes) causes an additional inclination of ELOG lattice planes with respect to those in the buffer. A qualitative explanation of these findings is presented taking into account increase of GaN grain size in the ELOG layers.
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Papers by P. Prystawko