The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform
Patrick J. Mccann - One of the best experts on this subject based on the ideXlab platform.
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MBE-Grown IV-VI Semiconductor Structures for Thermal Conductivity Measurements
MRS Proceedings, 2012Co-Authors: Patrick J. Mccann, James D. Jeffers, Leonard Olona, Zhihua Cai, Khosrow NamjouAbstract:ABSTRACTIV-VI Semiconductor structures grown by molecular beam epitaxy (MBE) have been used to measure the cross-plane thermal conductivity of PbSe and PbSe/PbSnSe/PbSe multiperiod superlattice (SL) materials. Continuous wave photoluminescence (PL) measurements were used to determine epilayer temperatures localized to multiple quantum well (MQW) light emitting layers on top of various IV-VI materials structures. These data combined with finite element analysis (FEA) were used to extract cross-plane thermal conductivity values for different materials designs. Structures consisting of PbSe/PbSnSe/PbSe SL materials with multiple periodicities exhibited cross-plane lattice thermal conductivity values as low as 0.30 W/mK, a significant reduction relative to the 1.9 W/mK value for bulk PbSe. This work shows that lattice thermal conductivity reduction offers a highly viable approach for improving thermoelectric materials performance.
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IV-VI Semiconductor lasers for gas phase biomarker detection
Chemical and Biological Sensors for Industrial and Environmental Monitoring III, 2007Co-Authors: Patrick J. Mccann, Khosrow Namjou, Chad Roller, Gina Mcmillen, Pratyuma C. KamatAbstract:A promising absorption spectroscopy application for mid-IR lasers is exhaled breath analysis where sensitive, selective, and speedy measurement of small gas phase biomarker molecules can be used to diagnose disease and monitor therapies. Many molecules such as nitric oxide, ethane, formaldehyde, acetaldehyde, acetone, carbonyl sulfide, and carbon disulfide have been connected to diseases or conditions such as asthma, oxidative stress, breast cancer, lung cancer, diabetes, organ transplant rejection, and schizophrenia. Measuring these and other, yet to be discovered, biomarker molecules in exhaled breath with mid-IR lasers offers great potential for improving health care since such tests are non-invasive, real-time, and do not require expensive consumables or chemical reagents. Motivated by these potential benefits, mid-IR laser spectrometers equipped with presently available cryogenically-cooled IV-VI lasers mounted in compact Stirling coolers have been developed for clinical research applications. This paper will begin with a description of the development of mid-IR laser instruments and their use in the largest known exhaled breath clinical study ever performed. It will then shift to a description of recent work on the development of new IV-VI Semiconductor quantum well materials and laser fabrication methods that offer the promise of low power consumption (i.e. efficient) continuous wave emission at room temperature. Taken together, the demonstration of compelling clinical applications with large market opportunities and the clear identification of a viable pathway to develop low cost mid-IR laser instrumentation can create a renewed focus for future research and development efforts within the mid-IR materials and devices area.
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IV-VI Semiconductor Mid-IR Lasers
MRS Online Proceedings Library, 2006Co-Authors: Patrick J. Mccann, Yurii SelivanovAbstract:Mid-IR lasers fabricated from narrow bandgap IV-VI Semiconductors are proven devices for molecular spectroscopy applications. Wide single-mode tunability, low waste heat generation, and large spectral coverage from about 1000 cm^−1 (10 µm) to about 2500 cm^−1 (4 µm) have allowed development of laser absorption spectroscopy instrumentation for fast and sensitive measurement of specific gas phase molecules. For example, IV-VI mid-IR lasers with emission in the 5.2 µm spectral range have recently enabled the development of breath analysis instruments for real-time measurement of exhaled nitric oxide (eNO). Laser tunability with current ramping is sufficient for simultaneous measurement of exhaled carbon dioxide (eCO2), a capability that allows highly accurate determination of eNO concentrations in the low ppb range, a sensitivity required for assessing airway inflammation in patients with asthma. After discussing emerging medical diagnostic applications this paper reviews recent progress in the development of liquid-nitrogen-free cryogenic cooling systems for IV-VI mid-IR lasers. A description of continuing research on the development of improved IV-VI lasers, where the primary objective is to fabricate devices with continuous wave (cw) operation at room temperature is then presented. Theoretical and experimental analysis of (111)-oriented multiple quantum well (MQW) IV-VI materials show that it should be possible to reduce lasing thresholds significantly. In addition, results from transferring IV-VI materials from low thermal conductivity growth substrates to higher thermal conductivity copper show that new laser packaging methods can significantly improve active region heat dissipation. Together, these new materials and device packaging methods promise to enable the fabrication of IV-VI mid-IR lasers with cw operation at room temperature.
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Transfer of IV–VI multiple quantum well structures grown by molecular beam epitaxy from Si substrates to copper
Thin Solid Films, 2005Co-Authors: A. Sow, C. Yao, Patrick J. MccannAbstract:Abstract A novel epilayer bonding and substrate removal procedure is described for the fabrication of cleaved-cavity Fabry-Perot resonant cavity lasers. IV–VI Semiconductor multiple quantum well (MQW) structures grown on silicon host substrates by molecular beam epitaxy with a CaF 2 buffer layer were successfully transferred to the tips of an assembled array of copper bars, which were then separated after substrate removal to cleave the epilayer structure. Scanning electron microscope images show that this bonding, substrate removal, and cleaving procedure can be used to create {110} and {112} cleaved facets in (111)-oriented IV–VI Semiconductor epitaxial layer structures. Photoluminescence data before and after transfer showed that the procedure did not degrade the optical properties of the MQW structures. This technique can enable the fabrication of edge-emitting lasers with improved active region heat dissipation properties.
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Optical pumping of IV-VI Semiconductor multiple quantum well materials using a GaSb-based laser with emission at λ=2.5μm
Journal of Applied Physics, 2005Co-Authors: Patrick J. Mccann, P.c. Kamat, A. Sow, Gregory Belenky, Leon Shterengas, J. G. Kim, Ramon U. MartinelliAbstract:Room-temperature photoluminescence (PL) measurements of IV-VI Semiconductor multiple quantum well (MQW) structures using diode laser optical pumping at two different excitation wavelengths, 2.5 and 0.91μm, are described. Active region temperatures during continuous-wave optical pumping were determined from blueshifts in PL emission energies. Temperatures were between 22.7 and 29.5°C lower for 2.5-μm pumping as compared to 0.91-μm pumping at the same power level of 100mW. Heating effects are also shown to be smaller for MQW samples with more narrow PbSe wells.
Gunther Springholz - One of the best experts on this subject based on the ideXlab platform.
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Molecular Beam Epitaxy of IV–VI Semiconductors: Fundamentals, Low-dimensional Structures, and Device Applications
Molecular Beam Epitaxy, 2018Co-Authors: Gunther SpringholzAbstract:Abstract Molecular beam epitaxy of IV–VI Semiconductor multilayers, quantum dots (QD), and device applications are described. The properties of the IV–VI compounds differ in several respects from zinc blende III–V or II–VI Semiconductors. This has significant consequences on the growth processes of molecular beam epitaxy as well as for the electronic properties of quantum wells and superlattices. QDs can be obtained by the Stranski–Krastanov growth mode as well as by epitaxial phase separation and nanoprecipitation. In the first case, excellent three-dimensional ordering and stacking of QDs in superlattices can be achieved due to the high elastic anisotropy, leading to the formation of three-dimensional QD crystals. In the second case, strong mid-infrared emission of QDs at room temperature has been obtained that is tunable over a wide spectral region. The main application of IV–VI or lead salt compounds is in mid-infrared optoelectronic devices, and examples for diode lasers, vertical cavity surface-emitting laser, and microdisc lasers are described.
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Molecular beam epitaxy of IV–VI Semiconductors: multilayers, quantum dots and device applications
Molecular Beam Epitaxy, 2013Co-Authors: Gunther SpringholzAbstract:Molecular beam epitaxy of IV–VI Semiconductor multilayers, quantum dots and device applications is described. The properties of the IV–VI compounds differ in several respects from zinc blende III–V or II–VI Semiconductors. This has significant consequences on the growth processes of molecular beam epitaxy as well as for the electronic properties of quantum wells and superlattices. Quantum dots can be obtained by the Stranski–Krastanov growth mode as well as by epitaxial phase separation and nanoprecipitation. In the first case, excellent three-dimensional ordering and stacking of quantum dots in superlattices can be achieved due to the high elastic anisotropy, leading to the formation of three-dimensional quantum dot crystals. In the second case, strong mid-infrared emission of quantum dots at room temperature has been obtained that is tunable over a wide spectral region. The main application of IV–VI or lead salt compounds is in mid-infrared optoelectronic devices, and examples for diode lasers, vertical cavity surface-emitting laser (VCSELs) and microdisc lasers are described.
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Molecular beam epitaxy of IV–VI Semiconductor hetero‐ and nano‐structures
physica status solidi (b), 2007Co-Authors: Gunther Springholz, Gerrit E. W. BauerAbstract:In this review, molecular beam epitaxy of IV–VI Semiconductor hetero- and nanostructures is described. The properties of the IV–VI compounds differ in several respects from zinc-blende III–V or II–VI Semiconductors. This has significant consequences on the growth processes of molecular beam epitaxy. The main application of IV–VI or lead salt compounds is in mid-infrared optoelectronic devices. As example, the growth of lead salt lasers is described with special emphasis on vertical cavity surface emitting lasers. Furthermore, it is shown that due to the large elastic anisotropy of IV–VI compounds, self-organized quantum dot superlattices show remarkable ordering and vertical correlations. As a result, 3D ordered quantum dot crystals can be obtained. Thus, these materials are ideal model systems for the investigation of lateral, vertical and staggered dot ordering in multilayer structures. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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Mid-infrared high finesse microcavities and vertical-cavity lasers based on IV–VI Semiconductor/BaF2 broadband Bragg mirrors
Journal of Applied Physics, 2007Co-Authors: Th Schwarzl, W. Heiß, Gunther Springholz, M. Eibelhuber, E. Kaufmann, A. Winter, H PascherAbstract:We report on molecular beam epitaxially grown high-reflectivity broadband Bragg mirrors for mid-infrared devices using IV–VI Semiconductors and BaF2. This material combination exhibits a high ratio between the refractive indices of up to 3.5, leading to a broad mirror stop band with a relative width of 75%. To verify the high quality of the PbEuTe/BaF2 Bragg mirrors, we study a half-wavelength microcavity formed by mirrors with only three periods. The resonance of the microcavity has a narrow linewidth of 5.2 nm corresponding to a very high finesse of 750. From this, a mirror reflectivity higher than 99.7% is deduced, in good agreement to transfer matrix simulations. Furthermore, we demonstrate mid-infrared continuous-wave vertical-cavity surface-emitting lasers based on these mirrors. Optical excitation of laser structures with a PbSe active region results in stimulated emission at various cavity modes between 7.3 and 5.9 μm at temperatures between 54 and 135 K. Laser emission is evidenced by a strong li...
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CH4/H2 plasma etching of IV-VI Semiconductor nanostructures
Semiconductor Science and Technology, 1999Co-Authors: Th Schwarzl, W. Heiß, Gudrun Kocher-oberlehner, Gunther SpringholzAbstract:We investigate plasma etching of IV-VI nanostructures using a CH 4 /H 2 gas mixture. For various IV-VI compounds we find that the etch rate decreases with the energy band gap. For Pb 1-x Eu x Te, in contrast, the etch rate decreases drastically with increasing Eu content. This property can be utilized for selective etching. Furthermore, we demonstrate IV-VI quantum wires with vertical side walls by a combination of laser holography and CH 4 /H 2 /Ar plasma etching.
Th Schwarzl - One of the best experts on this subject based on the ideXlab platform.
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Mid-infrared high finesse microcavities and vertical-cavity lasers based on IV–VI Semiconductor/BaF2 broadband Bragg mirrors
Journal of Applied Physics, 2007Co-Authors: Th Schwarzl, W. Heiß, Gunther Springholz, M. Eibelhuber, E. Kaufmann, A. Winter, H PascherAbstract:We report on molecular beam epitaxially grown high-reflectivity broadband Bragg mirrors for mid-infrared devices using IV–VI Semiconductors and BaF2. This material combination exhibits a high ratio between the refractive indices of up to 3.5, leading to a broad mirror stop band with a relative width of 75%. To verify the high quality of the PbEuTe/BaF2 Bragg mirrors, we study a half-wavelength microcavity formed by mirrors with only three periods. The resonance of the microcavity has a narrow linewidth of 5.2 nm corresponding to a very high finesse of 750. From this, a mirror reflectivity higher than 99.7% is deduced, in good agreement to transfer matrix simulations. Furthermore, we demonstrate mid-infrared continuous-wave vertical-cavity surface-emitting lasers based on these mirrors. Optical excitation of laser structures with a PbSe active region results in stimulated emission at various cavity modes between 7.3 and 5.9 μm at temperatures between 54 and 135 K. Laser emission is evidenced by a strong li...
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6 spl mu m vertical cavity surface emitting laser based on iv vi Semiconductor compounds
Electronics Letters, 2000Co-Authors: Th Schwarzl, G. Springholz, W Heiss, M Aigle, H PascherAbstract:An optically-pumped lead salt-based vertical cavity surface emitting laser is presented. The laser structure grown by molecular-beam epitaxy consists of a Pb0.99Eu0.01Te/PbTe λ/2 microcavity with Pb0.99Eu0.01Te/Pb0.94Eu0.06Te Bragg mirrors. Stimulated emission was observed at 6073 nm below 25 K.
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plasma etching of IV-VI Semiconductor nanostructures
Semiconductor Science and Technology, 1999Co-Authors: Th Schwarzl, W. Heiß, Gudrun Kocher-oberlehner, G. SpringholzAbstract:We investigate plasma etching of IV-VI nanostructures using a gas mixture. For various IV-VI compounds we find that the etch rate decreases with the energy band gap. For , in contrast, the etch rate decreases drastically with increasing Eu content. This property can be utilized for selective etching. Furthermore, we demonstrate IV-VI quantum wires with vertical side walls by a combination of laser holography and /Ar plasma etching.
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CH4/H2 plasma etching of IV-VI Semiconductor nanostructures
Semiconductor Science and Technology, 1999Co-Authors: Th Schwarzl, W. Heiß, Gudrun Kocher-oberlehner, Gunther SpringholzAbstract:We investigate plasma etching of IV-VI nanostructures using a CH 4 /H 2 gas mixture. For various IV-VI compounds we find that the etch rate decreases with the energy band gap. For Pb 1-x Eu x Te, in contrast, the etch rate decreases drastically with increasing Eu content. This property can be utilized for selective etching. Furthermore, we demonstrate IV-VI quantum wires with vertical side walls by a combination of laser holography and CH 4 /H 2 /Ar plasma etching.
G. Springholz - One of the best experts on this subject based on the ideXlab platform.
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self organized growth of three dimensional iv vi Semiconductor quantum dot crystals with fcc like vertical stacking and tunable lattice constant
Surface Science, 2000Co-Authors: G. Springholz, M Pinczolits, V Holy, Peter Mayer, Karin Wiesauer, T Roch, G. BauerAbstract:Abstract Heteroepitaxial growth of highly lattice-mismatched Semiconductor layers has evolved as a novel method for direct synthesis of self-assembled quantum dots based on the Stranski–Krastanov growth mode. In this growth mode, nano-scale three-dimensional (3D) islands are spontaneously formed on the epitaxial surface once the layer thickness exceeds a certain critical coverage. In multilayer structures, the interaction of the strained islands via their long-range elastic strain fields may lead to a vertical and lateral ordering of the dots. Here, it is shown that the elastic anisotropy and the growth orientation play a crucial role for this self-organization process. In particular, for (111)-oriented IV–VI Semiconductor (PbSe/Pb 1− x Eu x Te) multilayers, the direction of the interlayer dot correlations is shown to be inclined to the surface normal. This leads to a fcc-like ABCABC … vertical dot stacking sequence, which is particularly effective for inducting a lateral ordering of the dots as well. As a result, large domains of trigonally ordered 3D quantum dot crystals are formed, and their lattice constant can be tuned continuously just by changing the thickness of the spacer between the quantum dot layers.
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6 spl mu m vertical cavity surface emitting laser based on iv vi Semiconductor compounds
Electronics Letters, 2000Co-Authors: Th Schwarzl, G. Springholz, W Heiss, M Aigle, H PascherAbstract:An optically-pumped lead salt-based vertical cavity surface emitting laser is presented. The laser structure grown by molecular-beam epitaxy consists of a Pb0.99Eu0.01Te/PbTe λ/2 microcavity with Pb0.99Eu0.01Te/Pb0.94Eu0.06Te Bragg mirrors. Stimulated emission was observed at 6073 nm below 25 K.
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plasma etching of IV-VI Semiconductor nanostructures
Semiconductor Science and Technology, 1999Co-Authors: Th Schwarzl, W. Heiß, Gudrun Kocher-oberlehner, G. SpringholzAbstract:We investigate plasma etching of IV-VI nanostructures using a gas mixture. For various IV-VI compounds we find that the etch rate decreases with the energy band gap. For , in contrast, the etch rate decreases drastically with increasing Eu content. This property can be utilized for selective etching. Furthermore, we demonstrate IV-VI quantum wires with vertical side walls by a combination of laser holography and /Ar plasma etching.
W. Heiß - One of the best experts on this subject based on the ideXlab platform.
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Mid-infrared high finesse microcavities and vertical-cavity lasers based on IV–VI Semiconductor/BaF2 broadband Bragg mirrors
Journal of Applied Physics, 2007Co-Authors: Th Schwarzl, W. Heiß, Gunther Springholz, M. Eibelhuber, E. Kaufmann, A. Winter, H PascherAbstract:We report on molecular beam epitaxially grown high-reflectivity broadband Bragg mirrors for mid-infrared devices using IV–VI Semiconductors and BaF2. This material combination exhibits a high ratio between the refractive indices of up to 3.5, leading to a broad mirror stop band with a relative width of 75%. To verify the high quality of the PbEuTe/BaF2 Bragg mirrors, we study a half-wavelength microcavity formed by mirrors with only three periods. The resonance of the microcavity has a narrow linewidth of 5.2 nm corresponding to a very high finesse of 750. From this, a mirror reflectivity higher than 99.7% is deduced, in good agreement to transfer matrix simulations. Furthermore, we demonstrate mid-infrared continuous-wave vertical-cavity surface-emitting lasers based on these mirrors. Optical excitation of laser structures with a PbSe active region results in stimulated emission at various cavity modes between 7.3 and 5.9 μm at temperatures between 54 and 135 K. Laser emission is evidenced by a strong li...
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plasma etching of IV-VI Semiconductor nanostructures
Semiconductor Science and Technology, 1999Co-Authors: Th Schwarzl, W. Heiß, Gudrun Kocher-oberlehner, G. SpringholzAbstract:We investigate plasma etching of IV-VI nanostructures using a gas mixture. For various IV-VI compounds we find that the etch rate decreases with the energy band gap. For , in contrast, the etch rate decreases drastically with increasing Eu content. This property can be utilized for selective etching. Furthermore, we demonstrate IV-VI quantum wires with vertical side walls by a combination of laser holography and /Ar plasma etching.
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CH4/H2 plasma etching of IV-VI Semiconductor nanostructures
Semiconductor Science and Technology, 1999Co-Authors: Th Schwarzl, W. Heiß, Gudrun Kocher-oberlehner, Gunther SpringholzAbstract:We investigate plasma etching of IV-VI nanostructures using a CH 4 /H 2 gas mixture. For various IV-VI compounds we find that the etch rate decreases with the energy band gap. For Pb 1-x Eu x Te, in contrast, the etch rate decreases drastically with increasing Eu content. This property can be utilized for selective etching. Furthermore, we demonstrate IV-VI quantum wires with vertical side walls by a combination of laser holography and CH 4 /H 2 /Ar plasma etching.
