arXiv subjects

Henryk Turski

Publications and source records attributed to Henryk Turski.

13 recordsLinked to original sources

arXiv2026

Micro-transfer Printed Blue InGaN Lasers on Silicon Nitride Photonic Integrated Circuits

Expanding integrated photonics into the blue spectral range requires high-performance light sources, making the gallium nitride (GaN) material family indispensable. While silicon nitride (SiN) platforms offer a robust, CMOS compatible passive ecosystem for visible wavelengths, seamlessly integrating GaN lasers remains a major bottleneck. Conventional heterogeneous integration methods present distinct trade-offs: full-wafer bonding achieves high throughput but requires careful management of thermal and lattice mismatches across large areas, whereas flip-chip bonding ensures high yield through pretesting but is constrained by sequential processing speed. In this landscape, micro-transfer printing (MTP) emerges as a disruptive, material-efficient alternative, bypassing these limitations by combining high-density parallel integration with known-good-die selection. Applying MTP to GaN, however, presents a significant material challenge: due to its chemical inertness and strong III-N bonds, device release typically relies on electrochemical etching, which can compromise material quality. Here, we overcome this hurdle and demonstrate the first micro-transfer printed blue lasers on a SiN platform. Using a heavily doped n-type sacrificial layer together with optimized electrochemical etching conditions, we release smooth-surfaced thin-film light sources from bulk GaN substrates. Following release, the devices are integrated and butt-coupled to SiN fork-shaped edge couplers, achieving high current densities exceeding 20 kA$/$cm$^2$ alongside lasing at 455 nm. These results expand the visible integrated photonic toolkit and establish a framework for multi-wavelength integration, opening new avenues for next-generation technologies including flow cytometry, quantum computing, optical communications, and augmented/virtual reality.

physics.optics↗

arXiv2026

Efficient Quasi-Resonant, Polarization-Selective Excitation of GaN Quantum Emitters

Defect centers in GaN emerge as bright sources of single-photons which recently have been demonstrated to optically interface a localized spin. However, the structure and composition of these defects as well as their efficient excitation techniques were not a subject of thorough studies. This work presents evidence that by tuning the excitation laser energy to specific resonance values the excitation efficiency can be enhanced, resulting in relative increase of photoluminescence intensity by up to an order of magnitude. The resonances can be selectively addressed with linearly polarized light, while the emission dipole remains unchanged, enabling polarization-controlled enhancement. These results establish an efficient way of excitation for GaN-based emitters, thereby increasing the generation rate of photons. The data is consistent with excitation via localized vibrational modes associated with point-defect complexes, establishing a practical quasi-resonant route to brighter, polarization-addressable operation of GaN defect emitters and clarifying their energy-level structure.

cond-mat.mtrl-sci↗

arXiv2025

Edge emission from 265~nm UV-C LEDs grown by MBE on bulk AlN

UV-C LEDs pseudomorphically grown by MBE on bulk AlN substrates emitting at 265 nm are demonstrated. High current density up to 800 A/cm$^2$, 5 orders of on/off ratio, and low differential on-resistance of 2.6 m$Ω\cdot$cm$^2$ at the highest current density is achieved. The LED heterostructure has a high refractive index waveguide core surrounded by n- and p-cladding layers similar to a laser diode designed for mode confinement at 270 nm to facilitate edge emission and collection of photons. Edge-emitting devices are made by cleaving the fabricated LEDs along the $m$-plane of the wurtzite crystal. Electrical injection results in emission of high energy 4.7 eV photons that are collected from the cleaved edge of the LEDs corresponding to the optical bandgap of the AlGaN active region. The contribution of power dissipation across the n- and p-regions of the diode is discussed. The n-contact resistance to n-AlGaN is identified as the largest contributor to the series resistance of the LED in the present generation of devices.

physics.optics↗

arXiv2025

Off-resonant photoluminescence spectroscopy of high-optical quality single photon emitters in GaN

In this work, we analyze the relevance of excitation parameters on the emission from single-photon emitting defect centers in GaN. We investigate the absorption spectrum of different emitters by photoluminescence excitation technique at 10\,K. We report large spectral jumps (shifts up to 22\,meV) in the emitters' zero-phonon line (ZPL). The likelihood of such jumps is increased by the change in excitation energy. The shifts indicate a large built-in dipole moment of the defects and suggest a possibility to electrically tune their ZPL in a wide range. From the photoluminescence excitation studies, we observe that for majority of the emitters the absorption peaks exist between 2 and 2.55\,eV. The absorption peaks vary from emitter to emitter, and no universal absorption pattern is apparent. Finally, for selected emitters we observe significantly reduced spectral diffusion and instrument-limited linewidth of $138\,μeV$ (0.04\,nm).These findings show a new perspective for atomic defect GaN emitters as sources of coherent photons, shine new light on their energy level structure and show the possibility of tuning the ZPL, paving the way to fully harness their potential for applications in quantum technologies.

cond-mat.mtrl-sci↗

arXiv2024

Leveraging both faces of polar semiconductor wafers for functional devices

Unlike non-polar semiconductors such as silicon, the broken inversion symmetry of the wide bandgap semiconductor gallium nitride leads to a large electronic polarization along a unique crystal axis. This makes the two surfaces of the semiconductor wafer perpendicular to the polar axis dramatically different in their physical and chemical properties. In the last three decades, the cation (gallium) face of gallium nitride has been used for photonic devices such as LEDs and lasers. Though the cation face has also been predominantly used for electronic devices, the anion (nitrogen) face has recently shown promise for high electron mobility transistors due to favorable polarization discontinuities. In this work we introduce dualtronics, showing that it is possible to make photonic devices on the cation face, and electronic devices on the anion face, of the same semiconductor wafer. This opens the possibility for leveraging both faces of polar semiconductors in a single structure, where electronic, photonic, and acoustic properties can be implemented on opposite faces of the same wafer, dramatically enhancing the functional capabilities of this revolutionary semiconductor family.

physics.app-ph↗

arXiv2022

Impact of interfaces on photoluminescence efficiency of high indium content InGaN quantum wells

InGaN-based light emitting diodes (LEDs) are known to suffer from low electron and hole wavefunction overlap due to high piezoelectric field. Staggered InGaN quantum wells (QWs) have been proposed to increase the wavefunction overlap and improve the efficiency of LEDs especially for long wavelength emitters. In this work we evidence that the growth of staggered QWs has also another beneficial effect as it allows to reduce the formation of defects, responsible for nonradiative Shockley-Read-Hall recombination, at the bottom interface of the QW. Staggered QWs comprised an InGaN layer of an intermediate In content between the barrier and the QW. We show that insertion of such a layer results in a significant increase of the luminescence intensity, even if the calculated wavefunction overlap drops. We study the dependence of the thickness of such an intermediate In content layer on photoluminescence (PL) intensity behavior. Staggered QWs exhibit increased cathodoluminescence (CL) homogeneity that is a fingerprint of lower density of defects, in contrast to standard QWs for which high density of dark spots are observed in QW emission mapping. Transmission electron microscopy of standard QWs revealed formation of basal-plane stacking faults (BSFs) and voids that could have resulted from vacancy aggregation. Stepwise increase of the In content in staggered QWs prevents formation of point defects and results in an increased luminescence efficiency. The In composition difference between the barrier and the well is therefore a key parameter to control the formation of point defects in the high-In content QWs, influencing the luminescence efficiency.

physics.optics↗

arXiv2022

Electrically pumped blue laser diodes with nanoporous bottom cladding

We demonstrate electrically pumped III-nitride edge-emitting laser diodes (LDs) with nanoporous bottom cladding. The LD structure was grown by plasma-assisted molecular beam epitaxy. Highly doped 350 nm thick GaN:Si cladding layer with Si concentration of 6 x 1019 cm-3 was electrochemically etched to obtain porosity of 15 +/- 3% with pore size of 20 +/- 9 nm. The devices with nanoporous bottom cladding are compared to the refer-ence structures. The pulse mode operation was obtained at 448.7 nm with a slope efficiency (SE) of 0.2 W/A while the reference device without etched cladding layer was lasing at 457 nm with SE of 0.56 W/A. The de-sign of the LDs with porous bottom cladding was modelled theoretically. Performed calculations allowed to choose the optimum porosity and thickness of the cladding needed for the desired optical mode confinement and reduced the risk of light leakage to the substrate and to the top-metal contact. This demonstration opens new possibilities for the fabrication of III-nitride LDs.

physics.app-ph↗

arXiv2021

Dislocation and Indium Droplet Related Emission Inhomogeneities in InGaN LEDs

This report classifies emission inhomogeneities that manifest in InGaN quantum well blue light-emitting diodes grown by plasma-assisted molecular beam epitaxy on free-standing GaN substrates. By a combination of spatially resolved electroluminescence and cathodoluminescence measurements, atomic force microscopy, scanning electron microscopy and hot wet KOH etching, the identified inhomogeneities are found to fall in four categories. Labeled here as type I through IV, they are distinguishable by their size, density, energy, intensity, radiative and electronic characteristics and chemical etch pits which correlates them with dislocations. Type I exhibits a blueshift of about 120 meV for the InGaN quantum well emission attributed to a perturbation of the active region, which is related to indium droplets that form on the surface in the metal-rich InGaN growth condition. Specifically, we attribute the blueshift to a decreased growth rate of and indium incorporation in the InGaN quantum wells underneath the droplet which is postulated to be the result of reduced incorporated N species due to increased N$_{2}$ formation. The location of droplets are correlated with mixed type dislocations for type I defects. Types II through IV are due to screw dislocations, edge dislocations, and dislocation bunching, respectively, and form dark spots due to leakage current and nonradiative recombination.

cond-mat.mtrl-sci↗

arXiv2020

Inhomogeneous broadening of optical transitions observed in photoluminescence and modulated reflectance of polar and non-polar InGaN quantum wells

In this work the broadening of interband transitions in InGaN/GaN quantum wells (QWs) resulting from structural inhomogeneities is analyzed. The role of polarization-induced electric field in the mechanism behind the inhomogeneous broadening observed in photoluminescence (PL) and electromodulated reflectance (ER) spectra of InGaN QWs dedicated to green/blue lasers is explained. Spectra of both polar and non-polar QWs are simulated within the random QW model distinguishing contributions of individual transitions taking into account QW inhomogeneities (QW width and indium content fluctuations). On this basis we interpret the ER and PL spectra measured for a polar multiple QW InGaN/GaN structure. The built-in electric field shifts the emission wavelength to red, and enhances the broadening of optical transitions. It is clearly shown that for polar QWs the Stokes shift can be easily overestimated if PL spectra are compared with ER spectra since the intensity of the fundamental transition observed in ER spectra significantly decreases with the increase in QW width. In this way ER signal related to excited states start to dominate. This effect is strongly enhanced by QW inhomogeneities.

cond-mat.mes-hall↗

arXiv2019

Enhanced injection efficiency and light output in bottom tunnel-junction light-emitting diodes using UID GaN spacers

Recently, the use of bottom-TJ geometry in LEDs, which achieves N-polar-like alignment of polarization fields in conventional metal-polar orientations, has enabled enhancements in LED performance due to improved injection efficiency. Here, we elucidate the root causes behind the enhanced injection efficiency by employing mature laser diode structures with optimized heterojunction GaN/In$_{0.17}$Ga$_{0.83}$N/GaN TJs and UID GaN spacers to separate the optical mode from the heavily doped absorbing p-cladding regions. In such laser structures, polarization offsets at the electron blocking layer, spacer, and quantum barrier interfaces play discernable roles in carrier transport. By comparing a top-TJ structure to a bottom-TJ structure, and correlating features in the electroluminescence, capacitance-voltage, and current-voltage characteristics to unique signatures of the N- and Ga-polar polarization heterointerfaces in energy band diagram simulations, we identify that improved hole injection at low currents, and improved electron blocking at high currents, leads to higher injection efficiency and higher output power for the bottom-TJ device throughout 5 orders of current density (0.015 - 1000 A/cm$^2$). Moreover, even with the addition of a UID GaN spacer, differential resistances are state-of-the-art, below 7x10-4 $Ω$cm$^2$. These results highlight the virtues of the bottom-TJ geometry for use in high-efficiency laser diodes.

physics.app-ph↗

arXiv2018

Highly efficient optical transition between excited states in wide InGaN quantum wells

There is a lack of highly efficient light emitting devices (LEDs) operating in the green spectral regime. The devices based on (In,Al)GaN show extremely high efficiencies in violet and blue colors but fall short for longer emission wavelengths due to the quantum confined Stark effect (QCSE). In this paper we present a design of the active region based on wide InGaN quantum wells (QWs) which do not suffer from QCSE and profit from an enhancement in the internal quantum efficiency (IQE). The design exploits highly efficient optical transitions between excited states. It is shown that, counterintuitively, the devices with higher InGaN composition exhibit a higher enhancement in IQE. Experimental evidence is provided showing a gradual change in the nature of the optical transition with increasing thickness of the QW. Moreover, optical gain in long wavelength LDs incorporating standard and wide QWs is investigated to show the utilization of our concept.

physics.app-ph↗

arXiv2018

Polarization control in Nitride Quantum Well Light Emitters Enabled by Bottom Tunnel-junctions

The frozen internal polarization-induced electric fields due to broken inversion symmetry in all conventional blue and green nitride semiconductor light emitting semiconductor quantum well heterostructures point in a direction opposite to what is desired for efficient flow of electrons and holes. This state of affairs has persisted because of the desire to have p-type hole injectors on top of the quantum well active region. Because of the internal polarization fields in nitride heterostructures, there exist four permutations of doping and polarization for the realization of such light emitters. Which permutation is the most desirable for efficient light emission? In this work, we answer this question by demonstrating a fundamentally new approach towards efficient light emission with bottom-tunnel junctions. The bottom-tunnel junction design aligns the polarization fields in a desired direction in the quantum well, while simultaneously eliminating the need for p-type contacts, and allowing efficient current spreading. By preventing electron overshoot past quantum wells, it disables carrier recombination in undesired regions of the quantized heterostructures, and opens up the possibility for new geometries of integrating and stacking multiple light emitters. Due to the inherent advantages, the bottom-tunnel junction light emitting diode enables a 200-300% increase in the light emission efficiency over alternate heterostructure designs.

physics.app-ph↗

arXiv2015

Miscut dependent surface evolution in the process of N-polar GaN$(000\bar 1)$ growth under N-rich condition

The evolution of surface morphology during the growth of N-polar (000-1) GaN under N-rich condition is studied by kinetic Monte Carlo (kMC) simulations for two substrates miscuts 2deg and 4deg. The results are compared with experimentally observed surface morphologies of (000-1) GaN layers grown by plasma-assisted molecular beam epitaxy. The proposed kMC two-component model of GaN(000-1) surface where both types of atoms: nitrogen and gallium attach the surface and diffuse independently, explains that at relatively high rates of the step flow (miscut angle <2deg) the low diffusion of gallium adatoms causes surface instabilities and leads to experimentally observed roughening while for low rates of the step flow (miscut 4deg), smooth surface can be obtained. In the presence of almost immobile nitrogen atoms under N-rich conditions, the growth is realized by the process of two-dimensional island nucleation and coalescence. Additionally, we show that higher crystal miscut, lower crystal growth rate or higher temperature results in similar effect of the smoothening of the surface. We show that the surface also smoothens for the growth conditions with very high N-excess. The presence of large number of nitrogen atoms changes locally mobility of gallium atoms thus providing easier coalescence of separated island.

cond-mat.mtrl-sci↗