A5082593058- GaN-based semiconductor devices and materials
- Ga2O3 and related materials
- ZnO doping and properties
- Photocathodes and Microchannel Plates
- Semiconductor Quantum Structures and Devices
- Skin Protection and Aging
- Semiconductor materials and devices
- Spectroscopy and Laser Applications
- Metal and Thin Film Mechanics
- Semiconductor Lasers and Optical Devices
- Photodynamic Therapy Research Studies
- Infection Control and Ventilation
- Gas Sensing Nanomaterials and Sensors
- Plasma Diagnostics and Applications
- Biosensors and Analytical Detection
- Advanced Sensor and Energy Harvesting Materials
- Library Science and Information Systems
- Thermal Radiation and Cooling Technologies
- Impact of Light on Environment and Health
- Thin-Film Transistor Technologies
- Photoacoustic and Ultrasonic Imaging
- Artificial Intelligence in Law
- Photonic and Optical Devices
- Wound Healing and Treatments
- Atmospheric Ozone and Climate
Technische Universität Berlin
2015-2024
Ferdinand-Braun-Institut
2022-2024
Kirchhoff (Germany)
2022-2024
University College Cork
2016
The performance characteristics of AlGaN-based deep ultraviolet light emitting diodes (UV-LEDs) grown by metalorganic vapor phase epitaxy on sputtered and high temperature annealed AlN/sapphire templates are investigated compared with LEDs epitaxially laterally overgrown (ELO) AlN/sapphire. structural electro-optical properties the devices 350 nm show similar defect densities output power levels as low density ELO templates. After annealing AlN, full widths at half maximum (0002) (101¯2)...
The design and Mg-doping profile of AlN/Al0.7Ga0.3N electron blocking heterostructures (EBH) for AlGaN multiple quantum well (MQW) light emitting diodes (LEDs) below 250 nm was investigated. By inserting an AlN layer (EBL) into the EBH, we were able to increase emission power significantly reduce long wavelength parasitic luminescence. Furthermore, leakage suppressed by optimizing thickness EBL while still maintaining sufficient hole injection. Ultraviolet (UV)-C LEDs with very low...
The optical polarization of emission from ultraviolet (UV) light emitting diodes (LEDs) based on (0001)-oriented AlxGa1−xN multiple quantum wells (MQWs) has been studied by simulations and electroluminescence measurements. With increasing aluminum mole fraction in the well x, in-plane intensity transverse-electric (TE) polarized decreases relative to that transverse-magnetic light, attributed a reordering valence bands AlxGa1−xN. Using k ⋅ p theoretical model calculations, AlGaN MQW active...
Multiresistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) cause serious postoperative infections. A skin tolerant far-UVC (< 240 nm) irradiation system for their inactivation is presented here. It uses UVC LEDs in combination with a spectral filter and provides peak wavelength of 233 nm, full width at half maximum 12 an irradiance 44 µW/cm
High temperature annealed AlN/sapphire templates exhibit a reduced in-plane lattice constant compared to conventional non-annealed grown by metalorganic vapor phase epitaxy (MOVPE). This leads additional mismatch between the template and AlGaN-based ultraviolet-C light emitting diode (UVC LED) heterostructure on these templates. introduces compressive strain in AlGaN quantum wells resulting enhanced transverse electric polarization of well emission at wavelengths below 235 nm layer...
Abstract The influence of aluminum mole fraction Al x Ga 1- N/Al y N multiple quantum wells (MQWs) on the optical polarization, light extraction efficiency (LEE) and external (EQE) deep ultra violet emitting diodes in wavelength range between 264 220 nm is investigated. on-wafer EQE decreases from 0.6% to 0.00013% this range. Polarization resolved photoluminescence electroluminescence measurements show a change dominant transverse-electric transverse-magnetic polarized emission with...
Deep UV-LEDs (DUV-LEDs) emitting at 233 nm with an emission power of (1.9 ± 0.3) mW and external quantum efficiency (0.36 0.07) % 100 mA are presented. The entire DUV-LED process chain was optimized including the reduction dislocation density using epitaxially laterally overgrown AlN/sapphire substrates, development vanadium-based low resistance n-metal contacts, employment high thermally conductive AlN packages. Estimated device lifetimes above 1500 h achieved after a burn-in h. With...
We report on the performance of AlGaN-based deep ultraviolet light-emitting diodes (UV-LEDs) emitting at 265 nm grown stripe-patterned high-temperature annealed (HTA) epitaxially laterally overgrown (ELO) aluminium nitride (AlN)/sapphire templates. For this purpose, structural and electro-optical properties ultraviolet-c (UVC-LEDs) as-grown HTA planar AlN/sapphire as well ELO with without are investigated compared. Cathodoluminescence measurements reveal dark spot densities <mml:math...
An extensive analysis of the degradation characteristics AlGaN-based ultraviolet light-emitting diodes emitting around 265 nm is presented. The optical power LEDs stressed at a constant dc current 100 mA (current density = 67 A/cm2 and heatsink temperature 20 °C) decreased to about 58% its initial value after 250 h operation. origin this effect has been studied using capacitance-voltage photocurrent spectroscopy measurements conducted before aging. overall device capacitance decreased, which...
We report on AlGaN-based tunnel heterojunctions grown by metalorganic vapor phase epitaxy enabling fully transparent UVC LEDs eliminating the absorbing p-AlGaN and p-GaN layers. Furthermore, electrical characteristics can be improved exploiting higher conductivity of n-AlGaN layers as well a lower resistance n-contacts. with AlGaN:Mg/AlGaN:Si junctions exhibiting single peak emission at 268 nm have been realized, demonstrating effective carrier injection into AlGaN multiple quantum active...
AlGaN-based far-UVC light emitting diodes (LEDs) with an emission wavelength of 233 nm were fabricated in the form micro-LED arrays emitter diameters ranging from 1.5 to 50 μm. The mesa was plasma etched a sidewall angle 45°–50°, and insulator layers made SiNx or SiO2 deposited. While external quantum efficiency (EQE) LEDs showed only small dependency on diameter, using increase peak EQE by factor four as compared large area devices. This enhancement is attributed strong extraction due total...
Ultraviolet light-emitting diodes (LEDs) suffer from a low wall-plug efficiency, which is to large extent limited by the poor light extraction efficiency (LEE). A thin-film flip-chip (TFFC) design with roughened N-polar AlGaN surface can substantially improve this. We here demonstrate an enabling technology realize TFFC LEDs emitting in UVB range (280-320 nm), includes standard LED processing combination electrochemical etching remove substrate. The integration of achieved epitaxial...
UV light emitters in the UV-B spectral range between 280 nm and 320 are of great interest for applications such as phototherapy, gas sensing, plant growth lighting, curing. In this paper we present high power LEDs grown by MOVPE on sapphire substrates. By optimizing heterostructure design, parameters processing technologies, significant progress was achieved with respect to internal efficiency, injection efficiency extraction. LED chips emitting at 310 maximum output powers up 18 mW have...
In this paper, we will present the development of a compact LED-based optical gas sensing system in ultraviolet-C spectral region. This includes design LED heterostructure emitting near 226 nm, an chip, and implementation into capable detecting nitrogen oxide concentrations ppm range.
The electrical and structural properties of V/Al-based n-contacts on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mi mathvariant="normal">n</mml:mi> <mml:mo>‐</mml:mo> <mml:msub> <mml:mi>Al</mml:mi> <mml:mi>x</mml:mi> </mml:msub> <mml:mi>Ga</mml:mi> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> </mml:mrow> mathvariant="normal">N</mml:mi> </mml:math> with an Al mole fraction id="m2"> ranging from id="m3"> <mml:mo>=</mml:mo> <mml:mn>0.75</mml:mn>...
The development of ultraviolet AlGaN multiple quantum well (MQW) light emitting diodes (LEDs) in the wavelength range between 239 and 217 nm is presented. effects aluminum composition MQW active region underlying AlxGa1−xN:Si current spreading layer on emission characteristics operating voltages are investigated. A strong reduction output power observed with decreasing which partly attributed to absorption within AlxGa1−xN:Si. Additionally, a reduced carrier injection efficiency identified...
The effect of different Al(Ga)N electron blocking heterostructures (EBH) on the emission spectra and light output power 290 nm emitting diodes (LEDs) has been investigated. carrier injection internal quantum efficiency LEDs is simulated compared to electroluminescence measurements. highest found for with an Mg-doped AlN/Al0.7Ga0.3N EBH AlN layer thickness &gt;3 nm. these was 8.5-times higher without EBH. This attributed improved confinement which prevents leakage into p-doped region LED...
This paper reports a comprehensive analysis of the origin electroluminescence (EL) peaks and thermal droop in UV-B AlGaN-based LEDs. By carrying out spectral measurements at several temperatures currents, (i) we extract information on physical various bands, (ii) we develop novel closed-form model based Shockley–Read–Hall theory ABC rate equation that is able to reproduce experimental data caused by non-radiative recombination through deep levels. In samples under test, three EL bands are...
Abstract The light extraction efficiency (LEE), external quantum (EQE), and current–voltage characteristics of deep ultraviolet emitting diodes (DUV-LEDs) with different aluminum mole fractions in the p-AlGaN layers have been investigated. Optimizing layer composition requires a tradeoff between reducing absorption losses limiting increases p-contact resistance operation voltage. AlGaN multiple well LEDs around 263 nm AlGaN:Mg short period super lattices (p-SPSL) ranging from x = 33%...
The impact of the operation parameters current and temperature on degradation AlGaN-based 233 nm far-ultraviolet-C LEDs is investigated. observed effects can be divided into two groups: First, a rapid reduction in optical power to about 50%–30% initial value during first ∼100 h operation, which accompanied by an increase below diffusion voltage from 0.3 1 μA, hydrogen concentration p-side close active region. second group represented gradual power, runs parallel dominates for times ≥100 h....
We investigate the impact of Mg-doping on performance and degradation kinetics AlGaN-based UV-C light-emitting diodes (LEDs). By comparing LEDs from three wafers with different nominal doping levels [Mg/(Al+Ga) ratio: 0.15%, 0.5%, 1% in gas phase during epitaxy] AlGaN:Mg electron-blocking layer (EBL), we demonstrate following results: (i) A higher EBL results a optical power at low current levels, which is ascribed to an increased hole injection efficiency. (ii) The reduction follows...
In order to realize UVB LEDs with high wall‐plug efficiencies, the light extraction efficiency from LED heterostructure must be maximized and operating voltages reduced. this study, we investigate effect of GaN:Mg contact layer thickness on light‐output current‐voltage characteristics LEDs. AlGaN‐based heterostructures, that are fully transparent for emission except grown by metal organic vapor phase epitaxy c‐plane sapphire substrates. From transfer line measurements, it is found p‐contact...