M. Weyers
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View article: Impact of Silicon Doping on High‐Temperature Annealed AlN/Sapphire Templates
Impact of Silicon Doping on High‐Temperature Annealed AlN/Sapphire Templates Open
The threading dislocation density (TDD) of epitaxially grown AlN layers on sapphire substrates can be significantly decreased by high‐temperature annealing (HTA). This study employs a process to improve the material quality of such AlN lay…
View article: Analysis of the External Quantum Efficiency of 233 nm Far‐Ultraviolet‐C‐Light Emitting Diodes with Distributed Polarization Doped <i>p</i> ‐AlGaN‐Layers
Analysis of the External Quantum Efficiency of 233 nm Far‐Ultraviolet‐C‐Light Emitting Diodes with Distributed Polarization Doped <i>p</i> ‐AlGaN‐Layers Open
AlGaN‐based far‐ultraviolet‐C light emitting diodes (far‐UVC LEDs) with an emission wavelength of 233 nm and a peak external quantum efficiency () of 1% are explored to derive the radiative recombination efficiency (), the light extraction…
View article: GaAs-based photonic integrated circuit platform enabling monolithic ring-resonator-coupled lasers
GaAs-based photonic integrated circuit platform enabling monolithic ring-resonator-coupled lasers Open
This paper reports on a monolithically integrated gallium arsenide (GaAs)-based photonic integrated circuit platform for wavelengths around 1064 nm. Enabled by spatially selective quantum well removal and two-step epitaxial growth, it supp…
View article: Spatial correlation of defect-selective etching and dark luminescence spots in Al <sub>x</sub> Ga<sub>1−x </sub>N
Spatial correlation of defect-selective etching and dark luminescence spots in Al <sub>x</sub> Ga<sub>1−x </sub>N Open
Defect-selective etching with molten Ba(OH) 2 /MgO etch drops was performed on c -plane AlGaN layers covering the entire composition range between GaN and AlN. Regardless of the aluminum content, the etchant produced shallow, hexagonal etc…
View article: 226 nm Far‐Ultraviolet‐C Light Emitting Diodes with an Emission Power over 2 mW
226 nm Far‐Ultraviolet‐C Light Emitting Diodes with an Emission Power over 2 mW Open
Far‐ultraviolet‐C (far‐UVC) light emitting diodes (LED) emitting at an emission wavelength of 226 nm with different n‐AlGaN contact layers, quantum well barriers, and quantum well numbers are compared regarding their emission power, operat…
View article: AlGaN/AlN heterostructures: an emerging platform for nonlinear integrated photonics
AlGaN/AlN heterostructures: an emerging platform for nonlinear integrated photonics Open
In the rapidly evolving area of integrated photonics, there is a growing need for materials that satisfy the particular requirements of increasingly complex and specialized devices and applications. Present photonic material platforms have…
View article: Telecom‐Band Spontaneous Parametric Down‐Conversion in AlGaAs‐on‐Insulator Waveguides
Telecom‐Band Spontaneous Parametric Down‐Conversion in AlGaAs‐on‐Insulator Waveguides Open
Widespread commercial adoption of telecom‐band quantum key distribution (QKD) will require fully integrated, room‐temperature transmitters. Implementing highly efficient spontaneous parametric down‐conversion (SPDC) on a platform that offe…
View article: GaN Drift Layers on Sapphire and GaN Substrates for 1.2 kV Class Vertical Power Devices
GaN Drift Layers on Sapphire and GaN Substrates for 1.2 kV Class Vertical Power Devices Open
The development of processes for epitaxial growth of vertical gallium nitride (GaN) drift layers enabling 1.2 kV breakdown voltage on low‐cost sapphire substrates is presented in comparison to GaN bulk substrates. The targeted blocking cap…
View article: Origin of the parasitic luminescence of 235 nm UVC LEDs grown on different AlN templates
Origin of the parasitic luminescence of 235 nm UVC LEDs grown on different AlN templates Open
AlN layers annealed at high temperatures offer low threading dislocation densities of mid 108 cm−2 and are therefore increasingly used as base layers in ultraviolet (UV) light emitting diode (LED) heterostructure growth. These LEDs, just l…
View article: High‐Temperature Annealing of Si‐Doped AlGaN
High‐Temperature Annealing of Si‐Doped AlGaN Open
This study explores the impact of Si doping on the material properties of high‐temperature annealed (HTA) Al 0.71 Ga 0.29 N layers, which are grown on AlN/sapphire templates. The AlGaN layers are doped with Si by applying different IV/III …
View article: Telecom-Band SPDC in AlGaAs-on-Insulator Waveguides
Telecom-Band SPDC in AlGaAs-on-Insulator Waveguides Open
Widespread commercial adoption of telecom-band quantum-key-distribution (QKD) will require fully integrated, room-temperature transmitters. Implementing highly efficient spontaneous parametric down-conversion (SPDC) on a platform that offe…
View article: AlGaN/AlN heterostructures: an emerging platform for nonlinear integrated photonics
AlGaN/AlN heterostructures: an emerging platform for nonlinear integrated photonics Open
In the rapidly evolving area of integrated photonics, there is a growing need for materials that satisfy the particular requirements of increasingly complex and specialized devices and applications. Present photonic material platforms have…
View article: Imaging Threading Dislocations and Surface Steps in Nitride Thin Films Using Electron Backscatter Diffraction
Imaging Threading Dislocations and Surface Steps in Nitride Thin Films Using Electron Backscatter Diffraction Open
Extended defects, like threading dislocations, are detrimental to the performance of optoelectronic devices. In the scanning electron microscope, dislocations are traditionally imaged using diodes to monitor changes in backscattered electr…
View article: 234 nm far-ultraviolet-C light-emitting diodes with polarization-doped hole injection layer
234 nm far-ultraviolet-C light-emitting diodes with polarization-doped hole injection layer Open
Far-ultraviolet-C (far-UVC) light-emitting diodes (LEDs) with an emission wavelength of 234 nm with different polarization-doped AlGaN hole injection layers (HILs) are compared regarding their emission power, voltage, and leakage current. …
View article: Role of Oxygen Incorporation in High Temperature Annealed AlGaN
Role of Oxygen Incorporation in High Temperature Annealed AlGaN Open
High‐temperature annealing (HTA) is a powerful technique to decrease dislocation density in AlN, which can also be applied on AlGaN. This work investigates the impact of using sapphire and AlN as a material cover during the face‐to‐face HT…
View article: Strain induced power enhancement of far-UVC LEDs on high temperature annealed AlN templates
Strain induced power enhancement of far-UVC LEDs on high temperature annealed AlN templates Open
High temperature annealed AlN/sapphire templates exhibit a reduced in-plane lattice constant compared to conventional non-annealed AlN/sapphire grown by metalorganic vapor phase epitaxy (MOVPE). This leads to additional lattice mismatch be…
View article: High-power diode lasers with in-situ-structured lateral current blocking for improved threshold, efficiency and brightness
High-power diode lasers with in-situ-structured lateral current blocking for improved threshold, efficiency and brightness Open
We present high-power GaAs-based broad-area diode lasers with a novel variant of the enhanced self-aligned lateral structure ‘eSAS’, having a strongly reduced lasing threshold and improved peak conversion efficiency and beam quality in com…
View article: Monolithically Integrated Extended Cavity Diode Laser with 32 kHz 3 dB Linewidth Emitting at 1064 nm
Monolithically Integrated Extended Cavity Diode Laser with 32 kHz 3 dB Linewidth Emitting at 1064 nm Open
The spectral linewidth of semiconductor lasers is a crucial performance parameter in a growing number of applications. A common method to improve the coherence of the laser relies on increasing the optical cavity length by an extended sect…
View article: Distributed Bragg reflector lasers emitting between 696 and 712 nm
Distributed Bragg reflector lasers emitting between 696 and 712 nm Open
The authors report on design, fabrication, and electro‐optical characterization of single‐frequency diode lasers emitting around 696, 707, and 712 nm. This has been achieved by a variation of the periods of the 10th order surface Bragg gra…
View article: Passively Q-switched microchip laser based picosecond light source in the visible-red to near-infrared band for semiconductor excitation
Passively Q-switched microchip laser based picosecond light source in the visible-red to near-infrared band for semiconductor excitation Open
We developed a visible-red to near-infrared wavelength tunable all-solid-state laser system utilizing an optical parametric generation process in a MgO doped PPLN crystal pumped at 532 nm by an amplified and frequency doubled picosecond pa…
View article: Impact of Si doping on dislocation behavior in MOVPE-grown AlN on high-temperature annealed AlN buffer layers
Impact of Si doping on dislocation behavior in MOVPE-grown AlN on high-temperature annealed AlN buffer layers Open
In this work, we compare the defect structure in unintentionally doped and Si-doped AlN layers grown by metalorganic vapor phase epitaxy (MOVPE) on high-temperature annealed (HTA) sputtered AlN templates on sapphire substrates. Since the H…
View article: Molten Barium Hydroxide as Defect Selective Drop Etchant for Dislocation Analysis on Aluminum Nitride Layers
Molten Barium Hydroxide as Defect Selective Drop Etchant for Dislocation Analysis on Aluminum Nitride Layers Open
In this article, the suitability of the etchants NaOH/KOH and Ba(OH) 2 for defect etching of metalorganic vapour‐phase epitaxy (MOVPE) grown AlN layers with a MgO‐assisted “drop method” is compared. Defect selectivity for the new etchant B…
View article: Impact of operation parameters on the degradation of 233 nm AlGaN-based far-UVC LEDs
Impact of operation parameters on the degradation of 233 nm AlGaN-based far-UVC LEDs Open
The impact of the operation parameters current and temperature on the degradation of AlGaN-based 233 nm far-ultraviolet-C LEDs is investigated. The observed effects can be divided into two groups: First, a rapid reduction in the optical po…
View article: Temperature Dependence of Dark Spot Diameters in GaN and AlGaN
Temperature Dependence of Dark Spot Diameters in GaN and AlGaN Open
Threading dislocations in c‐plane (Al,Ga)N layers are surrounded by areas with reduced light generation efficiency, called “dark spots.” These areas are observable in luminescence measurements with spatial resolution in the submicrometer r…
View article: A carbon-doping related luminescence band in GaN revealed by below bandgap excitation
A carbon-doping related luminescence band in GaN revealed by below bandgap excitation Open
Carbon doped GaN grown by hydride vapor phase epitaxy was investigated by photoluminescence and photoluminescence excitation spectroscopy covering a broad range of carbon concentrations. Above bandgap excitation reveals typical transitions…