Dr. rer. nat. Mykhaylo Semtsiv
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Forschungsthemen1
Novel miniaturized photoacoustic cell integrated with compact mid-infrared widely-tunable laser for gas-detection applications
Quelle ↗Zeitraum: 05/2014 - 04/2016 Projektleitung: Dr. rer. nat. Mykhaylo Semtsiv
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Publikationen25
Top 25 nach Zitationen — Quelle: OpenAlex (BAAI/bge-m3 embedded für Matching).
Applied Optics · 977 Zitationen · DOI
The complex refractive index components, n and k, have been studied for thin films of several common dielectric materials with a low to medium refractive index as functions of wavelength and stoichiometry for mid-infrared (MIR) wavelengths within the range 1.54-14.29 μm (700-6500 cm(-1)). The materials silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, and titanium oxide are prepared using room temperature reactive sputter deposition and are characterized using MIR variable angle spectroscopic ellipsometry. The investigation shows how sensitive the refractive index functions are to the O2 and N2 flow rates, and for which growth conditions the materials deposit homogeneously. It also allows conclusions to be drawn on the degree of amorphousness and roughness. To facilitate comparison of the materials deposited in this work with others, the index of refraction was also determined and provided for the near-IR and visible ranges of the spectrum. The results presented here should serve as a useful information base for designing optical coatings for the MIR part of the electromagnetic spectrum. The results are parameterized to allow them to be easily used for coating design.
Nanotechnology · 105 Zitationen · DOI
A theory based on the Bardeen formalism is developed for computing the tunnel current between a metal tip and a semiconductor surface. Tip-induced band bending in the semiconductor is included, with the electrostatic potential computed in a fully three-dimensional model whereas the tunnel current is computed in the limit of large tip radii. Localized states forming at the semiconductor surface as well as wavefunction tailing through the semiconductor depletion region are fully accounted for. Numerical results are provided and compared with data obtained from p-type GaAs surfaces, and generalization of the method to semiconductor heterojunctions is discussed.
Iron doped InGaAs: Competitive THz emitters and detectors fabricated from the same photoconductor
2017Journal of Applied Physics · 101 Zitationen · DOI
Today, the optimum material systems for photoconductive emitters and receivers are different. In THz reflection measurements, this leads to complicated optics or performance compromises. We present photoconductive emitters and detectors fabricated from molecular beam epitaxy (MBE) grown iron (Fe) doped InGaAs, which are well suited for a THz time-domain spectroscopy as both emitters and detectors. As a photoconductive emitter, 75 μW ± 5 μW of radiated THz power was measured. As a detector, THz pulses with a bandwidth of up to 6 THz and a peak dynamic range of 95 dB could be detected. These results are comparable to state-of-the-art THz photoconductors, which allows for simple reflection measurements without a performance decrease. The incorporation of Fe in InGaAs during MBE growth is investigated by secondary ion mass spectroscopy, Hall, and transient differential transmission measurements. Growth temperatures close to 400 °C allow for homogeneous Fe doping concentrations up to 5 × 1020 cm−3 and result in a photoconductor with an electron lifetime of 0.3 ps, a resistivity of 2 kΩ cm, and an electron mobility higher than 900 cm2 V−1 s−1. We show that iron dopants are incorporated up to a maximum concentration of 1 × 1017 cm−3 into substitutional lattice sites. The remaining dopants are electrically inactive and form defects that are anneal-stable up to a temperature of 600 °C. The fast recombination center in Fe-doped InGaAs is an unidentified defect, representing ≈0.5% of the nominal iron concentration. The electron and hole capture cross section of this defect is determined as σe = 3.8 × 10−14 cm2 and σh = 5.5 × 10−15 cm2, respectively.
Applied Physics Letters · 79 Zitationen · DOI
We investigate photoconductive terahertz (THz) emitters compatible with 1550 nm excitation for THz time-domain spectroscopy (TDS). The emitters are based on rhodium (Rh) doped InGaAs grown by molecular beam epitaxy. InGaAs:Rh exhibits a unique combination of ultrashort trapping time, high electron mobility, and high resistivity. THz emitters made of InGaAs:Rh feature an emitted THz power of 637 μW at 28 mW optical power and 60 kV/cm electrical bias field. In particular for a fiber coupled photoconductive emitter, this is an outstanding result. When these emitters are combined with InGaAs:Rh based receivers in a THz TDS system, 6.5 THz bandwidth and a record peak dynamic range of 111 dB can be achieved for a measurement time of 120 s.
Monolithically Integrated InAs/GaAs Quantum Dot Mid-Infrared Photodetectors on Silicon Substrates
2016ACS Photonics · 78 Zitationen · DOI
High-performance, multispectral, and large-format infrared focal plane arrays are the long-demanded third-generation infrared technique for hyperspectral imaging, infrared spectroscopy, and target identification. A promising solution is to monolithically integrate infrared photodetectors on a silicon platform, which offers not only low-cost but high-resolution focal plane arrays by taking advantage of the well-established Si-based readout integrated circuits. Here, we report the first InAs/GaAs quantum dot (QD) infrared photodetectors monolithically integrated on silicon substrates by molecular beam epitaxy. The III–V photodetectors are directly grown on silicon substrates by using a GaAs buffer, which reduces the threading dislocation density to ∼106 cm–2. The high-quality QDs grown on Si substrates have led to long photocarrier relaxation time and low dark current density. Mid-infrared photodetection up to ∼8 μm is also achieved at 80 K. This work demonstrates that III–V photodetectors can directly be integrated with silicon readout circuitry for realizing large-format focal plane arrays as well as mid-infrared photonics in silicon.
Applied Physics Letters · 75 Zitationen · DOI
The design and implementation of a short-wavelength quantum-cascade laser based on the strain-compensated In0.73Ga0.27As–In0.55Al0.45As–AlAs heterosystem on InP is described. Lasers with a reduced level of doping in the active region require a larger bias voltage and emit at shorter wavelength; the emission wavelength is 3.05μm at T≈80K. The lasers operate up to T≈150K and electroluminescence persists up to room temperature, where the peak position is close to 3.3μm. The short-wavelength limit of such lasers is evaluated based on the dependence of their maximum operation temperatures and on the probable energies of the indirect valleys in the active region.
Applied Physics Letters · 68 Zitationen · DOI
Rhodium (Rh)-doped In0.53Ga0.47As grown by gas-source molecular beam epitaxy is investigated as a terahertz (THz) detector antenna for optical excitation at 1550 nm. The 4d transition metal rhodium acts as a deep level and ultrafast trapping center. At a doping concentration around 8 × 1019 cm−3, InGaAs:Rh exhibits ideal properties for application as a THz antenna: an ultrashort carrier lifetime below 200 fs in combination with a mobility of 1010 cm2/Vs. The THz detectors fabricated from this sample show a record peak dynamic range of 105 dB and a bandwidth of up to 6.5 THz.
Applied Physics Letters · 64 Zitationen · DOI
We demonstrate the design and implementation of a broad-gain and low-threshold (Jth=860A∕cm2 at 8K) quantum-cascade laser emitting between 3.7 and 4.2μm. The active region design is based on strain-compensated In0.73Ga0.27As–AlAs on InP. Laser operation in pulsed mode is achieved up to a temperature of 330K with maximum single-facet output peak powers of 6W at 8K and 240mW at 296K. The temperature coefficient T0 is 119K.
Applied Physics Letters · 57 Zitationen · DOI
We describe the fabrication and operation of surface emitting second-order distributed feedback quantum cascade ring lasers. The devices exhibit single-mode emission at a wavelength of 3.95μm with a side mode suppression ratio of 25dB. A linear tuning coefficient of 0.13cm−1∕K is observed. A single longitudinal mode in the ring shaped resonator results in a highly symmetric far-field pattern and a low beam divergence, represented by a full width at half maximum of ∼3°. Based on these characteristics the presented compact coherent light source may find its way into today’s midinfrared spectroscopy applications.
Optics Express · 49 Zitationen · DOI
Mid-infrared hyperspectral imaging has in the past decade emerged as a promising tool for medical diagnostics. In this work, nonlinear frequency upconversion based hyperspectral imaging in the 6 to 8 µm spectral range is presented for the first time, using both broadband globar and narrowband quantum cascade laser illumination. AgGaS<sub>2</sub> is used as the nonlinear medium for sum frequency generation using a 1064 nm mixing laser. Angular scanning of the nonlinear crystal provides broad spectral coverage at every spatial position in the image. This study demonstrates the retrieval of series of monochromatic images acquired by a silicon based CCD camera, using both broadband and narrowband illumination and a comparison is made between the two illumination sources for hyperspectral imaging.
Optics Express · 43 Zitationen · DOI
We demonstrate the first lasing emission of a thermo-electrically cooled terahertz quantum cascade laser (THz QCL). A high temperature three-well THz QCL emitting at 3.8 THz is mounted to a novel five-stage thermoelectric cooler reaching a temperature difference of ΔT = 124 K. The temperature and time-dependent laser performance is investigated and shows a peak pulse power of 4.4 mW and a peak average output power of 100 μW for steady-state operation.
Journal of Applied Physics · 39 Zitationen · DOI
Scanning tunneling microscopy and spectroscopy are used to study InGaP∕GaAs heterojunctions with InGaAs-like interfaces. Band offsets are probed using conductance spectra, with tip-induced band bending accounted for using three-dimensional electrostatic potential simulations together with a planar computation of the tunnel current. Curve fitting of theory to experiment is performed. Using an InGaP band gap of 1.90eV, which is appropriate to the disordered InGaP alloy, a valence band offset of 0.38±0.01eV is deduced along with the corresponding conduction band offset of 0.10±0.01eV (type I band alignment).
Applied Physics Letters · 38 Zitationen · DOI
The dependence of the scattering rate between different electronic states in semiconductor heterostructures due to interface roughness on the barrier height is exploited to enhance the population inversion in intersubband lasers. Barriers with differing heights are used within a strain-compensated InGaAs-InAlAs heterostructure to either increase or decrease the interface-roughness scattering component for specific confined states. In particular, low barriers are used where the upper laser state has its highest probability, thus maximizing the lifetime of the upper laser state; the higher barriers are used where the lower laser state and the few subsequent confined states have their highest probabilities, thus minimizing the lifetime of the lower laser state. By combining differing barrier heights in this way, the lifetime of the upper laser state is increased, while simultaneously the lifetime of the lower laser state is decreased; thus, the population inversion is significantly enhanced. This design approach is demonstrated for a quantum-cascade laser emitting near 4 μm. The reduced scattering out of the upper laser level is reflected in a narrower electroluminescence spectrum of 26 meV and a reduced threshold current density of 1.75 kA/cm2 at room-temperature.
Applied Physics Letters · 36 Zitationen · DOI
We report on the fabrication and operation of quantum cascade ring lasers providing grating-coupled surface emission. The devices exhibit tunable far fields, ranging from spot- to ring-shaped symmetric beam cross sections, depending on the grating period. This—along with threshold current densities as low as for comparable Fabry–Pérot lasers—demonstrates the compatibility of reduced beam divergence and two-dimensional integrability, resulting in an attractive light source for applications in midinfrared spectroscopy and imaging.
Journal of Applied Physics · 33 Zitationen · DOI
The threshold condition for a 4-level quantum cascade laser (QCL)-active region is formulated to include thermally activated leakage of charge carriers from active region confined states into states with higher energy. A method is described and demonstrated to extract the associated thermal escape current density from measurements at laser threshold. This current is modeled by including both the temperature dependent subband-distribution of charge carriers and longitudinal optical-phonon probability. The method is used to analyze the thermally activated leakage of charge carriers in two short-wavelength strain-compensated InGaAs/InAlAs QCL-structures. The energies of the higher-lying states extracted from the model are in good agreement with the values calculated numerically within the effective-mass approximation. The estimated scattering time for the thermal activation process agrees with the expected value as well. Our approach offers a straightforward and accurate method to analyze and troubleshoot thermally activated leakage in new QCL-active region designs.
Journal of Applied Physics · 33 Zitationen · DOI
The effect of doping concentration on the performance of short-wavelength quantum-cascade lasers based on the strain-compensated InGaAs/InAlAs/AlAs heterostructure on InP, emitting at 3.8 μm, is investigated for average doping concentrations between 0.3 and 3.9×1017 cm−3 (sheet densities between 1.6 and 20.9×1011 cm−2). Although the threshold current density is rather independent of doping concentration, the maximum current density increases with doping and exhibits a saturation for the highest doping level. Other important performance characteristics such as differential quantum efficiency, peak optical emission power, slope efficiency, and maximum operating temperature are observed to be maximized for structures with an average doping of 2−3×1017 cm−3, corresponding to a sheet density of about 1.5×1012 cm−2.
Applied Physics Letters · 31 Zitationen · DOI
The impact of interface roughness (IFR)-scattering on the quantum efficiency of quantum-cascade lasers (QCLs) is demonstrated and analyzed both experimentally and theoretically. An InGaAs/InAlAs strain-compensated QCL emitting at λ ∼ 5.4 μm is analyzed in pulsed mode at liquid nitrogen temperatures. Measurements of the differential slope efficiency as a function of laser resonator length allow the pumping efficiency to be measured as a function of electron temperature. Excellent agreement is obtained when comparing the data to a calculation of the leakage current into higher-lying states via IFR-scattering, providing evidence of the importance of IFR-scattering on the QCLs quantum efficiency.
Applied Physics Letters · 28 Zitationen · DOI
The properties of rhodium (Rh) as a deep-level dopant in InGaAs lattice matched to InP grown by molecular beam epitaxy are investigated. When InGaAs:Rh is used as an ultrafast photoconductor, carrier lifetimes as short as 100 fs for optically excited electrons are measured. Rh doping compensates free carriers so that a near intrinsic carrier concentration can be achieved. At the same time, InGaAs:Rh exhibits a large electron mobility of 1000 cm2/V s. Therefore, this material is a very promising candidate for application as a semi-insulating layer, THz antenna, or semiconductor saturable absorber mirror.
Applied Physics Letters · 27 Zitationen · DOI
We have studied intersubband absorption in strain compensated InxGa1−xAs/AlAs/InyAl1−yAs multiple quantum wells and superlattices grown on InP. X-ray diffraction shows that the layers are pseudomorphically strained and exhibit slight compositional grading of the interfaces. Owing to the high AlAs barriers, the intersubband absorption can be tailored to wavelengths shorter than 2 μm. In some samples, a small, but non-negligible absorption is also observed with s-polarized light.
Applied Physics Letters · 24 Zitationen · DOI
We describe the design and implementation of a broad-area (w ≈ 30 μm) quantum-cascade laser operating in a continuous wave mode up to heat-sink temperatures beyond +100 °C. The room-temperature emission wavelength is 4.6 μm. The temperature gradient in the active region of such a wide laser stripe is essentially perpendicular to the epitaxial layers and the resulting steady-state active region temperature offset scales approximately with the square of the number of cascades. With only 10 cascades in the active region, the threshold electrical power density in the current quantum-cascade laser in the continuous-wave mode is as low as Vth × Ith = 3.8 V × 0.9 kA/cm2 = 3.4 kW/cm2 at room temperature for 2 mm-long two-side high-reflectivity coated laser stripe. A 4 mm-long one-side high-reflectivity coated laser stripe delivers in continuous-wave mode above 0.6 W at +20 °C and above 1.3 W at −27 °C (cooled with a single-stage Peltier element). A 2 mm-long two-side high-reflectivity coated laser stripe demonstrates continuous-wave lasing up to at least +102 °C (375 K). The thermal conductance, Gth, ranges between 235 W/K cm2 and 140 W/K cm2 for temperatures between −33 °C and +102 °C. This demonstration opens the route for continuous-wave power scaling of quantum-cascade lasers via broad-area laser ridges.
Semiconductor Science and Technology · 23 Zitationen · DOI
An InGaAs quantum dot (QD) photodetector is directly grown on a silicon substrate. GaAs-on-Si virtual substrates with a defect density in the order of 106 cm−2 are fabricated by using strained-layer superlattice as dislocation filters. As a result of the high quality virtual substrate, fabrication of QD layer with good structural properties has been achieved, as evidenced by transmission electron microscopy and x-ray diffraction measurements. The InGaAs QD infrared photodetector is then fabricated on the GaAs-on-Si wafer substrate. Dual-band photoresponse is observed at 80 K with two response peaks around 6 and 15 μm.
Applied Physics Letters · 21 Zitationen · DOI
The scattering of electrons out of the upper laser state into indirect valleys in quantum-cascade lasers is demonstrated by investigating the operation of the laser under the influence of magnetic fields up to 45 T. A quantum-cascade laser based on strain-compensated AlAs barriers and In0.73Ga0.27As/InAs wells, emitting with wavelength 3.1 μm, is investigated as a function of magnetic field normal to the surface. Minima in emission power are observed when Landau levels of the upper laser state are brought into resonance with states derived from the indirect valleys, leading to the partial depopulation of the upper laser level. The energy for the indirect valley states is determined to be about 640 meV above the bottom of the In0.73Ga0.27As Γ valley, about 70 meV above the upper laser level.
Applied Physics Letters · 20 Zitationen · DOI
Compositionally abrupt InGaP/GaAs heterojunctions grown by gas-source molecular-beam epitaxy have been investigated by cross-sectional scanning tunneling microscopy and spectroscopy. Images inside the InGaP layer show nonuniform In and Ga distribution. About 1.5 nm of transition region at the interfaces is observed, with indium carryover identified at the GaAs–on–InGaP interface. Spatially resolved tunneling spectra with nanometer spacing across the interface were acquired, from which band offsets (revealing that nearly all of band offset occurs in the valence band) were determined.
Optics Express · 19 Zitationen · DOI
A monolithic coupling scheme for mid-infrared quantum cascade laser arrays is investigated with respect to brightness enhancement. The tree-shaped resonator enables parallel coupling of six laser elements into a single element by means of several Y-junctions. Phase-locking is observed on the basis of far field analysis, and leads to in-phase emission on both sides of the device. The experimental results match calculated far field profiles and demonstrate a high level of modal control when driven far above threshold. Whereas optical power measurements confirm negligible coupling losses, the slope efficiency is below the theoretically expected value, which is attributed to modal competition. Additional evaluation of near fields and spectral characteristics provides background on the modal dynamics of the sophisticated cavity and reveals limitations to coherent beam combining. The findings pave the way to improved coupling efficiency and brightness scaling of a single facet emitting compact quantum cascade laser array.
Journal of Applied Physics · 19 Zitationen · DOI
Quantum-cascade lasers operating at λ≈3.9μm at room temperature with narrow w≈5μm ridge widths are described. The lateral confinement due to the narrow ridge is similar to the vertical confinement and the resulting beam is circular in cross section with a single TM00 spatial mode. The beam divergence is 46° both parallel and perpendicular to the surface. The beam quality factor along the slow axis is about M2=1.6. The narrow ridges also increase the relative lateral heat dissipation from the active region, resulting in a thermal conductance per unit area of about Gth=380WK−1cm−2 for a 3mm long laser. Maximum average power is obtained with duty cycles between 10% and 30%; in spite of the very narrow ridge, the total average power with thermoelectric cooling exceeds 60mW with a peak power of 460mW. The circularly symmetric beam with very good beam quality suggests essentially zero astigmatism and indicates that these narrow-ridge quantum-cascade lasers are well suited for applications in midinfrared spectroscopy and imaging.
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Identität, Organisation und Kontakt aus HU-FIS.
- Name
- Dr. rer. nat. Mykhaylo Semtsiv
- Titel
- Dr. rer. nat.
- Fakultät
- Mathematisch-Naturwissenschaftliche Fakultät
- Institut
- Institut für Physik
- Arbeitsgruppe
- Experimentelle Physik (Elementaranregungen und Transport in Festkörpern)
- Telefon
- +49 30 2093-82192
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- 26.4.2026, 01:12:29