Lutz Kirste - Profile on Academia.edu (original) (raw)
Papers by Lutz Kirste
III-V based high-performance photodetectors in the non-visible regime – from UV to IR
Preparation of deep UV transparent AlN substrates with high structural perfection for optoelectronic devices
CrystEngComm, 2016
In this paper, the optimal growth conditions during the physical vapour transport of bulk AlN cry... more In this paper, the optimal growth conditions during the physical vapour transport of bulk AlN crystals are evaluated with regard to significantly increased deep UV transparency, while maintaining the high structural quality of the AlN crystals which are grown on N-polar c-facets. We show that carbon concentration [C], oxygen concentration [O], and the ratio between both concentrations [C]/[O] have a significant influence on the deep UV transparency. At 3[C] < [O] with [C] + [O] < 1019 cm−3, deep UV transparent AlN single crystals with absorption coefficients at around 265 nm (α265nm) smaller than 15 cm−1 can be prepared. These conditions can be achieved in the N-polar grown volume parts of the AlN crystals using growth temperatures in the range of TG = 2030–2050 °C and tungsten and tantalum carbide as getter materials for carbon and oxygen, respectively. Deep UV transparent AlN substrates (α265nm < 30 cm−1) ≥10 mm in diameter and of high crystalline perfection (rocking curve FWHM < 15 arcsec) are shown for the first time.
Journal of Applied Physics, Jul 28, 2019
Wurtzite Al 1−x Sc x N thin films with scandium Sc concentrations up to x = 0.41 were prepared by... more Wurtzite Al 1−x Sc x N thin films with scandium Sc concentrations up to x = 0.41 were prepared by reactive pulsed DC magnetron co-sputtering at heater temperatures between 300°C and 400°C on Al 2 O 3 substrates. Spectroscopic ellipsometry was used to determine the dielectric functions of wurtzite Al 1−x Sc x N by modeling the spectra with a three-layer model involving parametric oscillator functions for the Al 1−x Sc x N layers. By combining ellipsometry with transmission spectroscopy, we determined the composition dependence of the optical band gap E g. For x < 0.25, the experimentally determined band gap follows the theoretical prediction with an offset, which arises from residual sub-band gap absorption. For higher Sc concentrations, for which the band gap is expected to become indirect, the experimental data deviate from the theoretical values for the direct band gap. No absorption that can be attributed to cubic ScN crystallites was observed up to x = 0.41, indicating a high phase purity in line with X-ray diffraction data.
Applied Physics Letters, Mar 9, 2020
Non-polar a-plane Al 0.77 Sc 0.23 N 1120 ð Þ thin films were prepared by magnetron sputter epitax... more Non-polar a-plane Al 0.77 Sc 0.23 N 1120 ð Þ thin films were prepared by magnetron sputter epitaxy on r-plane Al 2 O 3 ð1102Þ substrates. Different substrate off-cut angles were compared, and the off-cut angle of 3 resulted in the best structural quality of the AlScN layer. Structural characterization by x-ray diffraction confirmed that single phase, wurtzite-type, a-plane AlScN 1120 ð Þ , surface acoustic wave resonators were fabricated with wavelengths k ¼ 2-10 lm (central frequency up to 1.7 GHz) with two orthogonal in-plane propagation directions. A strong dependence of electromechanical coupling on the in-plane orientation was observed. Compared to conventional c-plane AlScN based resonators, an increase of 185-1000% in the effective electromechanical coupling was achieved with only a fractional decrease of <10.5% in series resonance frequency.
Physica Status Solidi A-applications and Materials Science, Dec 29, 2019
Missile approach warning (MAW) systems of airborne military platforms require ultrasensitive dete... more Missile approach warning (MAW) systems of airborne military platforms require ultrasensitive detection capabilities in the solar-blind UV regime below 280 nm. Today, these needs are answered with UV photomultiplier tubes, which are bulky, complex, and require external filtering to suppress clutter signatures beyond 280 nm.This study investigates whether AlGaN focal plane array (FPA) detectors may develop into a viable alternative. The compact, lightweight, all-solid-state solution promises intrinsic solar blindness and excellent out-of-band suppression ratios realizable at affordable costs on large-area substrates. Yet, does today's state of technology allow mastering the fabrication processes so that the electrooptical performance is sufficient to achieve the required sensitivity? Herein, three device wafers are grown by metalorganic chemical vapor deposition and subsequently processed into detector arrays with a spatial resolution of 640 Â 512 pixels on a 15 μm pitch. After hybridization with an off-the-shelf capacitive transimpedance input amplifier (CTIA) read-out integrated circuit (ROIC), their electrooptical performance is characterized. The characterized FPAs show a very low percentage of defective pixels, excellent linearity at high photon fluxes, and, at low flux, their already remarkable sensitivity is limited by the off-the-shelf CTIA ROIC. Therefore, with further improvements MAW systems based on AlGaN FPAs seem feasible.
Applied Physics Letters, Nov 7, 2022
Paper published as part of the special topic on Piezoelectric Thin Films for MEMS ARTICLES YOU MA... more Paper published as part of the special topic on Piezoelectric Thin Films for MEMS ARTICLES YOU MAY BE INTERESTED IN Al 0.7 Sc 0.3 N butterfly-shaped laterally vibrating resonator with a figure-of-merit (k t 2 •Q m) over 146
Journal of vacuum science & technology, May 1, 2022
The epitaxial growth of high-quality AlN on sapphire substrates is challenging due to high lattic... more The epitaxial growth of high-quality AlN on sapphire substrates is challenging due to high lattice and thermal mismatch and low Aladatom mobility, which cause high dislocation density and rough surface morphology. High-temperature AlN (deposited at 1130 C) was grown on low-temperature AlN nucleation layers (880 C) with different V/III ratios and reactor pressures by metal-organic chemical vapor deposition. Surface and crystal quality was optimized using high V/III ratios. Thereby, slow layer-by-layer growth at high V/III laterally overgrows the 3D nucleation layer reducing the dislocation density, twist, and tilt in the crystal. This was as effective as multistep growth with increasing V/III. At high pressure of 95 mbar, step-bunching occurred. This indicates low surface supersaturation due to parasitic reactions in the gas phase. This was suppressed by low growth pressure of 50 mbar, while the crystal quality worsened.
Applied Surface Science, Jun 1, 2017
The effects of heat treatment and strontium (Sr) addition on the microstructure and mechanical pr... more The effects of heat treatment and strontium (Sr) addition on the microstructure and mechanical properties of ADC12 alloys were investigated, and two-stage solution treatment was introduced. The results indicated that the addition of Sr obviously refined the microstructure of ADC12 alloys. When 0.05 wt% Sr was added into the alloy, the eutectic Si phase was fully modified into fine fibrous structure; α-Al and β-Al 5 FeSi phases were best refined; and the eutectic Al 2 Cu phase was modified into block-like Al 2 Cu phase that continuously distributed at the grain boundary. The ultimate tensile strength (UTS) (270.63 MPa) and elongation (3.19%) were increased by 51.2% and 73.4% respectively compared with unmodified alloys. After the two-stage solution treatment (500 °C, 6 h+520 °C, 4 h), for 0.05 wt% Sr modified ADC12 alloys, the Si phases transformed into fine particle structure and Al 2 Cu phases were fully dissolved. The peak hardness value of the alloys processed by the two-stage solution treatment was increased by 8.3% and 6.8% respectively compared to solution treatment at 500 °C and 520 °C. After the aging treatment (175 °C, 7 h), the hardness and UTS were increased by 38.73% and 13.96% respectively when compared with the unmodified alloy.
An advanced Bragg diffraction imaging technique to characterize defects in SiC and GaN : Topic/category, e.g. AM: Advanced Metrology
Journal of Applied Physics, Jan 14, 2020
Multiply twinned particles (MTPs) are fascinating crystallographic entities with a number of cont... more Multiply twinned particles (MTPs) are fascinating crystallographic entities with a number of controllable properties originating from their symmetry and cyclic structure. In the focus of our studies are diamond MTPs hosting optically active defects-objects demonstrating a high application potential for emerging optoelectronic and quantum devices. In this work, we discuss the growth mechanisms along with the microstructural and optical properties of the MTPs aggregating high-density of "siliconvacancy" complexes on the specific crystal irregularities. It is demonstrated that the silicon impurities incite a rapid growth of MTPs via intensive formation of penetration twins on {100} facets of regular octahedral grains. We also show that the zero-phonon-line emission from the Si color centers embedded in the twin boundaries dominates in photo-and electroluminescence spectra of the MTP-based lightemitting devices defining their steady-state optical properties.
Micromachines, Aug 8, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
InGaAs infrared detector development for SWIR imaging applications
Proceedings of SPIE, Oct 25, 2013
ABSTRACT We report on materials and technology development for short-wave infrared photodetectors... more ABSTRACT We report on materials and technology development for short-wave infrared photodetectors based on InGaAs p-i-n and avalanche photodiodes (APDs). Using molecular beam epitaxy for the growth of thin layers with abrupt interfaces, which are required for optimized APD structures, excellent crystalline quality has been achieved for detector structures grown on 3-inch InP substrates. For the fabrication of focal plane detector arrays, we employed a mesa etching technology in order to compare the results with the commonly utilized planar technology. Camera detector arrays as well as test structures with various sizes and geometries for materials and process characterization are processed using a dry-etch mesa technology. Aspects of the process development are presented along with measured dark-current and photo-current characteristics of the detector devices.
Improved AlScN/GaN heterostructures grown by metal-organic chemical vapor deposition
Semiconductor Science and Technology, Jan 22, 2021
AlScN/GaN epitaxial heterostructures have raised much interest in recent years, because of the hi... more AlScN/GaN epitaxial heterostructures have raised much interest in recent years, because of the high potential of such structures for high-frequency and high-power electronic applications. Compared to conventional AlGaN/GaN heterostructures, the high spontaneous and piezoelectric polarization of AlScN can yield to a five-time increase in sheet carrier density of the two-dimensional electron gas formed at the AlScN/GaN heterointerface. Very promising radio-frequency device performance has been shown on samples deposited by molecular beam epitaxy. Recently, AlScN/GaN heterostructures have been demonstrated, which were processed by the more industrial compatible growth method metal-organic chemical vapor deposition (MOCVD). In this work, SiN x passivated MOCVD-grown AlScN/GaN heterostructures with improved structural quality have been developed. Analytical transmission electron microscopy, secondary ion mass spectrometry and high-resolution x-ray diffraction analysis indicate the presence of undefined interfaces between the epitaxial layers and an uneven distribution of Al and Sc in the AlScN layer. However, AlScN-based high-electron-mobility transistors (HEMT) have been fabricated and compared with AlN/GaN HEMTs. The device characteristics of the AlScN-based HEMT are promising, showing a transconductance close to 500 mS mm−1 and a drain current above 1700 mA mm−1.
Electrothermal Performance of AlGaN/GaN Lateral Transistors with >10 μm Thick GaN Buffer on 200 mm Diameter‐Engineered Substrates
Physica Status Solidi A-applications and Materials Science, Jun 19, 2023
Reduced non-thermal roll-over in violet-emitting GaInN wide-well LEDs grown on low-dislocation-density substrates
Proceedings of SPIE, Feb 12, 2009
Acta Physica Polonica A, Nov 1, 2011
In this work we present measurements of GaInN/GaN light emitting diodes (LEDs) with an active lay... more In this work we present measurements of GaInN/GaN light emitting diodes (LEDs) with an active layer consisting of three quantum wells made of Ga0.9In0.10N that have different widths (1.8 nm, 2.7 nm, 3.7 nm). A comparison of emission and absorption (photocurrent) on the same sample revealed a shift in energy, with the emission energy being significantly lower. The shifts are about 0.02 eV, 0.03 eV, and 0.04 eV for the quantum wells having the widths of 1.8 nm, 2.7 nm, and 3.7 nm, respectively. This can be explained by a shift of the ground state energy caused by the quantum confined Stark effect. Calculations show that due to the spontaneous polarization and the piezoelectric effect a strong electric field of the order of 1 MV/cm was present in the GaInN quantum wells. Simulations of ground-state energies in the model of an infinite square well under the influence of an electric field with a matched effective well width were performed and used to interpret the experimental results.
Proceedings of SPIE, Feb 10, 2011
Improving the crystal quality of AlGaN epitaxial layers is essential for the realization of effic... more Improving the crystal quality of AlGaN epitaxial layers is essential for the realization of efficient III-nitride-based light emitting diodes (LEDs) with emission wavelengths below 365 nm. Here, we report on two different approaches to improve the material quality of AlGaN buffer layers for such UV-LEDs, which are known to be effective for the MOVPE growth of GaN layers. Firstly, we grew AlGaN on thin GaN nucleation islands which exhibit a threedimensional facetted structure (3D GaN nucleation). Lateral overgrowth of these islands results in a lateral bending of dislocation lines at the growing facets. Secondly, in-situ deposited SiN x interlayers have been used as nano-masks reducing the dislocation density above the SiN x layers. Both approaches result in reduced asymmetric HRXRD ω-scan peak widths, indicating a reduced edge-type dislocation density. They can be applied to the growth of AlGaN layers with an Al concentration of at least 20%, thus suitable for LEDs emitting around 350 nm. On-wafer electroluminescence measurements at 20 mA show an increase in output power by a factor of 7 and 25 for LED structures grown on 3D GaN nucleation and SiN x interlayer, respectively, compared to structures grown on a purely 2D grown low Al-content AlGaN nucleation layer. Mesa-LEDs fabricated from the LED layer sequences grown on buffers with SiN x interlayer exhibit a low forward voltage of 3.8 V at 20 mA and a maximum continuous wave (cw) output power of 12.2 mW at 300 mA.
Epitaxial growth of GaInAs/AlGaAsSb quantum cascade lasers
Journal of Crystal Growth, Apr 1, 2007
ABSTRACT
Current developments for type-II superlattice imaging systems
Proceedings of SPIE, May 13, 2011
InAs/GaSb-based type-II superlattice photodiodes have considerably gained interest as high-perfor... more InAs/GaSb-based type-II superlattice photodiodes have considerably gained interest as high-performance infrared detectors. Beside the excellent properties of InAs/GaSb superlattices, like the relatively high effective electron mass suppressing tunneling currents, the low Auger recombination rate, and a high quantum efficiency, the bandgap can be widely adjusted within the infrared spectral range from 3 - 30 mum depending on the layer thickness
Physica status solidi, Feb 29, 2012
We investigated the impact of SF 6 plasma treatments on the electronic transport properties of Ga... more We investigated the impact of SF 6 plasma treatments on the electronic transport properties of GaN/AlGaN/GaN heterostructures by employing different plasma conditions as well as annealing in nitrogen atmosphere at 425°C. The electrical properties are characterized by Hall-effect measurements while electron spectroscopy and X-ray measurements are used to investigate changes in the surface chemical composition and in the layer structure, respectively. It is demonstrated that plasma treatments strongly affect the 2DEG properties of the heterostructure due to altering of the surface potential accompanied by the formation of a thin fluorinated amorphous film. Increasing the DC bias voltage for the plasma treatment leads to an additional degradation of the mobility caused by incorporation of fluorine into the heterostructure interface. Furthermore, the thin GaN cap layer is etched by plasma treatments with higher bias potential, which increases the carrier density at the interface.
III-V based high-performance photodetectors in the non-visible regime – from UV to IR
Preparation of deep UV transparent AlN substrates with high structural perfection for optoelectronic devices
CrystEngComm, 2016
In this paper, the optimal growth conditions during the physical vapour transport of bulk AlN cry... more In this paper, the optimal growth conditions during the physical vapour transport of bulk AlN crystals are evaluated with regard to significantly increased deep UV transparency, while maintaining the high structural quality of the AlN crystals which are grown on N-polar c-facets. We show that carbon concentration [C], oxygen concentration [O], and the ratio between both concentrations [C]/[O] have a significant influence on the deep UV transparency. At 3[C] < [O] with [C] + [O] < 1019 cm−3, deep UV transparent AlN single crystals with absorption coefficients at around 265 nm (α265nm) smaller than 15 cm−1 can be prepared. These conditions can be achieved in the N-polar grown volume parts of the AlN crystals using growth temperatures in the range of TG = 2030–2050 °C and tungsten and tantalum carbide as getter materials for carbon and oxygen, respectively. Deep UV transparent AlN substrates (α265nm < 30 cm−1) ≥10 mm in diameter and of high crystalline perfection (rocking curve FWHM < 15 arcsec) are shown for the first time.
Journal of Applied Physics, Jul 28, 2019
Wurtzite Al 1−x Sc x N thin films with scandium Sc concentrations up to x = 0.41 were prepared by... more Wurtzite Al 1−x Sc x N thin films with scandium Sc concentrations up to x = 0.41 were prepared by reactive pulsed DC magnetron co-sputtering at heater temperatures between 300°C and 400°C on Al 2 O 3 substrates. Spectroscopic ellipsometry was used to determine the dielectric functions of wurtzite Al 1−x Sc x N by modeling the spectra with a three-layer model involving parametric oscillator functions for the Al 1−x Sc x N layers. By combining ellipsometry with transmission spectroscopy, we determined the composition dependence of the optical band gap E g. For x < 0.25, the experimentally determined band gap follows the theoretical prediction with an offset, which arises from residual sub-band gap absorption. For higher Sc concentrations, for which the band gap is expected to become indirect, the experimental data deviate from the theoretical values for the direct band gap. No absorption that can be attributed to cubic ScN crystallites was observed up to x = 0.41, indicating a high phase purity in line with X-ray diffraction data.
Applied Physics Letters, Mar 9, 2020
Non-polar a-plane Al 0.77 Sc 0.23 N 1120 ð Þ thin films were prepared by magnetron sputter epitax... more Non-polar a-plane Al 0.77 Sc 0.23 N 1120 ð Þ thin films were prepared by magnetron sputter epitaxy on r-plane Al 2 O 3 ð1102Þ substrates. Different substrate off-cut angles were compared, and the off-cut angle of 3 resulted in the best structural quality of the AlScN layer. Structural characterization by x-ray diffraction confirmed that single phase, wurtzite-type, a-plane AlScN 1120 ð Þ , surface acoustic wave resonators were fabricated with wavelengths k ¼ 2-10 lm (central frequency up to 1.7 GHz) with two orthogonal in-plane propagation directions. A strong dependence of electromechanical coupling on the in-plane orientation was observed. Compared to conventional c-plane AlScN based resonators, an increase of 185-1000% in the effective electromechanical coupling was achieved with only a fractional decrease of <10.5% in series resonance frequency.
Physica Status Solidi A-applications and Materials Science, Dec 29, 2019
Missile approach warning (MAW) systems of airborne military platforms require ultrasensitive dete... more Missile approach warning (MAW) systems of airborne military platforms require ultrasensitive detection capabilities in the solar-blind UV regime below 280 nm. Today, these needs are answered with UV photomultiplier tubes, which are bulky, complex, and require external filtering to suppress clutter signatures beyond 280 nm.This study investigates whether AlGaN focal plane array (FPA) detectors may develop into a viable alternative. The compact, lightweight, all-solid-state solution promises intrinsic solar blindness and excellent out-of-band suppression ratios realizable at affordable costs on large-area substrates. Yet, does today's state of technology allow mastering the fabrication processes so that the electrooptical performance is sufficient to achieve the required sensitivity? Herein, three device wafers are grown by metalorganic chemical vapor deposition and subsequently processed into detector arrays with a spatial resolution of 640 Â 512 pixels on a 15 μm pitch. After hybridization with an off-the-shelf capacitive transimpedance input amplifier (CTIA) read-out integrated circuit (ROIC), their electrooptical performance is characterized. The characterized FPAs show a very low percentage of defective pixels, excellent linearity at high photon fluxes, and, at low flux, their already remarkable sensitivity is limited by the off-the-shelf CTIA ROIC. Therefore, with further improvements MAW systems based on AlGaN FPAs seem feasible.
Applied Physics Letters, Nov 7, 2022
Paper published as part of the special topic on Piezoelectric Thin Films for MEMS ARTICLES YOU MA... more Paper published as part of the special topic on Piezoelectric Thin Films for MEMS ARTICLES YOU MAY BE INTERESTED IN Al 0.7 Sc 0.3 N butterfly-shaped laterally vibrating resonator with a figure-of-merit (k t 2 •Q m) over 146
Journal of vacuum science & technology, May 1, 2022
The epitaxial growth of high-quality AlN on sapphire substrates is challenging due to high lattic... more The epitaxial growth of high-quality AlN on sapphire substrates is challenging due to high lattice and thermal mismatch and low Aladatom mobility, which cause high dislocation density and rough surface morphology. High-temperature AlN (deposited at 1130 C) was grown on low-temperature AlN nucleation layers (880 C) with different V/III ratios and reactor pressures by metal-organic chemical vapor deposition. Surface and crystal quality was optimized using high V/III ratios. Thereby, slow layer-by-layer growth at high V/III laterally overgrows the 3D nucleation layer reducing the dislocation density, twist, and tilt in the crystal. This was as effective as multistep growth with increasing V/III. At high pressure of 95 mbar, step-bunching occurred. This indicates low surface supersaturation due to parasitic reactions in the gas phase. This was suppressed by low growth pressure of 50 mbar, while the crystal quality worsened.
Applied Surface Science, Jun 1, 2017
The effects of heat treatment and strontium (Sr) addition on the microstructure and mechanical pr... more The effects of heat treatment and strontium (Sr) addition on the microstructure and mechanical properties of ADC12 alloys were investigated, and two-stage solution treatment was introduced. The results indicated that the addition of Sr obviously refined the microstructure of ADC12 alloys. When 0.05 wt% Sr was added into the alloy, the eutectic Si phase was fully modified into fine fibrous structure; α-Al and β-Al 5 FeSi phases were best refined; and the eutectic Al 2 Cu phase was modified into block-like Al 2 Cu phase that continuously distributed at the grain boundary. The ultimate tensile strength (UTS) (270.63 MPa) and elongation (3.19%) were increased by 51.2% and 73.4% respectively compared with unmodified alloys. After the two-stage solution treatment (500 °C, 6 h+520 °C, 4 h), for 0.05 wt% Sr modified ADC12 alloys, the Si phases transformed into fine particle structure and Al 2 Cu phases were fully dissolved. The peak hardness value of the alloys processed by the two-stage solution treatment was increased by 8.3% and 6.8% respectively compared to solution treatment at 500 °C and 520 °C. After the aging treatment (175 °C, 7 h), the hardness and UTS were increased by 38.73% and 13.96% respectively when compared with the unmodified alloy.
An advanced Bragg diffraction imaging technique to characterize defects in SiC and GaN : Topic/category, e.g. AM: Advanced Metrology
Journal of Applied Physics, Jan 14, 2020
Multiply twinned particles (MTPs) are fascinating crystallographic entities with a number of cont... more Multiply twinned particles (MTPs) are fascinating crystallographic entities with a number of controllable properties originating from their symmetry and cyclic structure. In the focus of our studies are diamond MTPs hosting optically active defects-objects demonstrating a high application potential for emerging optoelectronic and quantum devices. In this work, we discuss the growth mechanisms along with the microstructural and optical properties of the MTPs aggregating high-density of "siliconvacancy" complexes on the specific crystal irregularities. It is demonstrated that the silicon impurities incite a rapid growth of MTPs via intensive formation of penetration twins on {100} facets of regular octahedral grains. We also show that the zero-phonon-line emission from the Si color centers embedded in the twin boundaries dominates in photo-and electroluminescence spectra of the MTP-based lightemitting devices defining their steady-state optical properties.
Micromachines, Aug 8, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
InGaAs infrared detector development for SWIR imaging applications
Proceedings of SPIE, Oct 25, 2013
ABSTRACT We report on materials and technology development for short-wave infrared photodetectors... more ABSTRACT We report on materials and technology development for short-wave infrared photodetectors based on InGaAs p-i-n and avalanche photodiodes (APDs). Using molecular beam epitaxy for the growth of thin layers with abrupt interfaces, which are required for optimized APD structures, excellent crystalline quality has been achieved for detector structures grown on 3-inch InP substrates. For the fabrication of focal plane detector arrays, we employed a mesa etching technology in order to compare the results with the commonly utilized planar technology. Camera detector arrays as well as test structures with various sizes and geometries for materials and process characterization are processed using a dry-etch mesa technology. Aspects of the process development are presented along with measured dark-current and photo-current characteristics of the detector devices.
Improved AlScN/GaN heterostructures grown by metal-organic chemical vapor deposition
Semiconductor Science and Technology, Jan 22, 2021
AlScN/GaN epitaxial heterostructures have raised much interest in recent years, because of the hi... more AlScN/GaN epitaxial heterostructures have raised much interest in recent years, because of the high potential of such structures for high-frequency and high-power electronic applications. Compared to conventional AlGaN/GaN heterostructures, the high spontaneous and piezoelectric polarization of AlScN can yield to a five-time increase in sheet carrier density of the two-dimensional electron gas formed at the AlScN/GaN heterointerface. Very promising radio-frequency device performance has been shown on samples deposited by molecular beam epitaxy. Recently, AlScN/GaN heterostructures have been demonstrated, which were processed by the more industrial compatible growth method metal-organic chemical vapor deposition (MOCVD). In this work, SiN x passivated MOCVD-grown AlScN/GaN heterostructures with improved structural quality have been developed. Analytical transmission electron microscopy, secondary ion mass spectrometry and high-resolution x-ray diffraction analysis indicate the presence of undefined interfaces between the epitaxial layers and an uneven distribution of Al and Sc in the AlScN layer. However, AlScN-based high-electron-mobility transistors (HEMT) have been fabricated and compared with AlN/GaN HEMTs. The device characteristics of the AlScN-based HEMT are promising, showing a transconductance close to 500 mS mm−1 and a drain current above 1700 mA mm−1.
Electrothermal Performance of AlGaN/GaN Lateral Transistors with >10 μm Thick GaN Buffer on 200 mm Diameter‐Engineered Substrates
Physica Status Solidi A-applications and Materials Science, Jun 19, 2023
Reduced non-thermal roll-over in violet-emitting GaInN wide-well LEDs grown on low-dislocation-density substrates
Proceedings of SPIE, Feb 12, 2009
Acta Physica Polonica A, Nov 1, 2011
In this work we present measurements of GaInN/GaN light emitting diodes (LEDs) with an active lay... more In this work we present measurements of GaInN/GaN light emitting diodes (LEDs) with an active layer consisting of three quantum wells made of Ga0.9In0.10N that have different widths (1.8 nm, 2.7 nm, 3.7 nm). A comparison of emission and absorption (photocurrent) on the same sample revealed a shift in energy, with the emission energy being significantly lower. The shifts are about 0.02 eV, 0.03 eV, and 0.04 eV for the quantum wells having the widths of 1.8 nm, 2.7 nm, and 3.7 nm, respectively. This can be explained by a shift of the ground state energy caused by the quantum confined Stark effect. Calculations show that due to the spontaneous polarization and the piezoelectric effect a strong electric field of the order of 1 MV/cm was present in the GaInN quantum wells. Simulations of ground-state energies in the model of an infinite square well under the influence of an electric field with a matched effective well width were performed and used to interpret the experimental results.
Proceedings of SPIE, Feb 10, 2011
Improving the crystal quality of AlGaN epitaxial layers is essential for the realization of effic... more Improving the crystal quality of AlGaN epitaxial layers is essential for the realization of efficient III-nitride-based light emitting diodes (LEDs) with emission wavelengths below 365 nm. Here, we report on two different approaches to improve the material quality of AlGaN buffer layers for such UV-LEDs, which are known to be effective for the MOVPE growth of GaN layers. Firstly, we grew AlGaN on thin GaN nucleation islands which exhibit a threedimensional facetted structure (3D GaN nucleation). Lateral overgrowth of these islands results in a lateral bending of dislocation lines at the growing facets. Secondly, in-situ deposited SiN x interlayers have been used as nano-masks reducing the dislocation density above the SiN x layers. Both approaches result in reduced asymmetric HRXRD ω-scan peak widths, indicating a reduced edge-type dislocation density. They can be applied to the growth of AlGaN layers with an Al concentration of at least 20%, thus suitable for LEDs emitting around 350 nm. On-wafer electroluminescence measurements at 20 mA show an increase in output power by a factor of 7 and 25 for LED structures grown on 3D GaN nucleation and SiN x interlayer, respectively, compared to structures grown on a purely 2D grown low Al-content AlGaN nucleation layer. Mesa-LEDs fabricated from the LED layer sequences grown on buffers with SiN x interlayer exhibit a low forward voltage of 3.8 V at 20 mA and a maximum continuous wave (cw) output power of 12.2 mW at 300 mA.
Epitaxial growth of GaInAs/AlGaAsSb quantum cascade lasers
Journal of Crystal Growth, Apr 1, 2007
ABSTRACT
Current developments for type-II superlattice imaging systems
Proceedings of SPIE, May 13, 2011
InAs/GaSb-based type-II superlattice photodiodes have considerably gained interest as high-perfor... more InAs/GaSb-based type-II superlattice photodiodes have considerably gained interest as high-performance infrared detectors. Beside the excellent properties of InAs/GaSb superlattices, like the relatively high effective electron mass suppressing tunneling currents, the low Auger recombination rate, and a high quantum efficiency, the bandgap can be widely adjusted within the infrared spectral range from 3 - 30 mum depending on the layer thickness
Physica status solidi, Feb 29, 2012
We investigated the impact of SF 6 plasma treatments on the electronic transport properties of Ga... more We investigated the impact of SF 6 plasma treatments on the electronic transport properties of GaN/AlGaN/GaN heterostructures by employing different plasma conditions as well as annealing in nitrogen atmosphere at 425°C. The electrical properties are characterized by Hall-effect measurements while electron spectroscopy and X-ray measurements are used to investigate changes in the surface chemical composition and in the layer structure, respectively. It is demonstrated that plasma treatments strongly affect the 2DEG properties of the heterostructure due to altering of the surface potential accompanied by the formation of a thin fluorinated amorphous film. Increasing the DC bias voltage for the plasma treatment leads to an additional degradation of the mobility caused by incorporation of fluorine into the heterostructure interface. Furthermore, the thin GaN cap layer is etched by plasma treatments with higher bias potential, which increases the carrier density at the interface.
IEEE Photonics Technology Letters, 2019
An indirect method to determine the internal polarization of a GaN/AlGaN-based quantum well is pr... more An indirect method to determine the internal polarization of a GaN/AlGaN-based quantum well is presented. The technique consists of carefully measuring the difference between the two lowest conduction subband levels under application of an electrical bias across the epitaxial layers. Due to a quantum confined Stark effect, the bound energy levels of the well show a strong frequency shift which depends on the size of the external field. Since this electric field was oriented oppositely to the internal polarization, partial screening of the latter occurred. By measuring these Stark shifts at three different fields, one was able to calculate the size of the internal polarization. Since the composition of the AlGaN barriers had previously been determined by X-ray diffraction, an extrapolated value of the internal polarization – as it would occur in a pure AlN/GaN interface – could be given. In agreement with the literature, a value of 720 MV/m was found.