
Markus WeyersFerdinand-Braun-Institut | FBH · Department of Materials Technology
Markus Weyers
Prof. Dr.
About
652
Publications
87,482
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12,863
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Introduction
Additional affiliations
September 1990 - March 1992
NTT Basic Resarch Lab
Position
- PostDoc Position
Description
- PostDoc working on gasphase growth of III-V semiconductors
Education
October 1980 - June 1990
Publications
Publications (652)
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 supports on-chip gain as well as passive waveguides. In addition, shallow- and deep-etched waveguides are realized....
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 supports on-chip gain as well as passive waveguides. In addition, shallow- and deep-etched waveguides are realized....
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 etch pits with depth-to-diameter ratios of 1/10–1/100. Two predominant types of etch pits were observed, which differ...
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, operation voltage, and lifetime. Electroluminescence measurements show higher emission power but also an increased op...
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 offers co‐integration of the pump laser has been an outstanding challenge. Here, using such a platform based on AlG...
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 made significant progress over the past years; however, each platform still faces specific material and perfor...
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 capability demands drift layers with a thickness of 10 μm and low but controllable n‐type doping. Using a growth r...
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 like those grown on conventional metalorganic vapor phase epitaxy (MOVPE) AlN templates, often suffer from long-...
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 ratios during epitaxial growth and compared to undoped Al 0.71 Ga 0.29 N. Before HTA, the threading dislocation...
AlGaN on AlN/Sapphire stands out in photonics for its strong nonlinearity, electro-optic modulability, and low loss in the visible spectrum. We fabricate and characterize AlGaN photonic devices, including ring resonators, directional couplers, and tapers.
We demonstrate 7-dB light amplification at 921 nm by transfer-printing a GaAs-based amplifier on a a-Si:H waveguide. This paves the way towards the development of evanescently-coupled integrated laser systems on SiN emitting in the near-infrared.
Static light-current-voltage (LIV) curves, spectrum, and far-field o f oxide-confined 7,19,100, and 312 vertical-cavity surface-emitting laser (VCSEL) arrays centered at 940 nm were collected to quantify scalability limits set by thermal coupling.
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 electron intensity as the electron beam is scanned over the sample, with the sample positioned so the electron beam i...
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. The influence of the thickness of the polarization-doped layer (PDL), an additional Mg doping of the PDL, as we...
The electroluminescence of UVB light-emitting diodes emitting at 310 nm before and after 1000 h of operation is studied in the temperature range from 20 to 340 K. Before operation, the external quantum efficiency (EQE) at 10 mA gradually increases with decreasing temperature from 0.8% at 340 K to 1.8% at 150 K and then levels off. This trend is att...
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 between the template and the AlGaN-based ultraviolet-C light emitting diode (UVC LED) heterostructure grown on th...
We report unprecedentedly low second harmonic band propagation losses in highly nonlinear AlGaAs-on-insulator waveguides pumped in the telecom L-band. These rafindings pave the way towards pa metric nonlinearities at single photon-level.
We report on the first observation of spontaneous parametric down-conversion and a highly efficient second harmonic generation with η shg ≈ 420 %/W/mm ² in AlGaAs- on-insulator waveguides operated at telecom wavelengths.
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 comparison to their standard gain-guided counterparts. To realize this new variant (eSAS-V2), a two-step epitaxial...
Growth of Si-doped AlN and of Al0.63Ga0.37N on high quality AlN templates grown by HVPE has been investigated. The strain state of Si-doped AlN is thickness-dependent due to the surface-mediated dislocation tilt which induces a tensile strain component. At very low dislocation density in the AlN buffer strain relaxation in micrometer-thick Al0.63Ga...
In this paper, we examine the carbon defects associated with peaks of infrared (IR) absorption and Raman scattering appearing in GaN crystals at carbon (C12) doping in the range of concentrations from 3.2×1017 to 3.5×1019cm−3. Here, 14 unique vibrational modes of defects are observed in GaN samples grown by HVPE (hydride vapor phase epitaxy) and th...
Abstract 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 gratings implemented on a single epitaxial wafer. Depending on the wavelength, the devices achieved an op...
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 section without gain material. Here, this extended cavity diode laser (ECDL) concept is realized in a monolithic de...
This work examines the carbon defects associated with recently reported and novel peaks of infrared (IR) absorption and Raman scattering appearing in GaN crystals at carbon ($^{12}C$) doping in the range of concentrations from $3.2*10^{17}$ to $3.5*10^{19} cm^{-3}$. 14 unique vibrational modes of defects are observed in GaN samples grown by hydride...
We present first results of our research towards ultra-short pulse generation in the sub-100 ps range based on cascaded gain-switched diodepumped vertical-cavity surface-emitting semiconductor lasers. In particular, we focus on the surface emitters themselves and on the dependence of the output parameters on the pump wavelength and the pump fluence...
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 passively Q-switched Nd:YVO4 microchip laser. A broad bandwidth, tuneable over 300 nm between 710 nm to 1015 nm,...
Increase of light extraction efficiency (LEE) and total output power of UV light emitting diodes (LEDs) emitting at 265 and 310 nm, respectively, after encapsulation with a UV-transparent silicone are studied. Raytracing simulations suggest that a properly placed hemispherical encapsulation with a refractive index in the range from 1.4 to 1.8 enhan...
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 HTA process leads to a reduction of the in-plane lattice constant of the AlN layers, further homoepitaxial overg...
In this paper we compare the suitability of the etchants NaOH/KOH and Ba(OH)2 for defect etching of MOVPE grown AlN layers with a MgO assisted “drop method”. Defect selectivity for the new etchant Ba(OH)2 is confirmed by local TEM‐analysis. Temperature dependence (420 °C – 500 °C) of etch‐pit sizes of a‐, mixed‐ and c‐type dislocations for both etc...
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 power to about 50%–30% of the initial value during the first ∼100 h of operation, which is accompanied by an incr...
AlGaN-based UVC light-emitting diodes (LED) were fabricated on high-quality AlN templates with an engineerable in-plane lattice constant. The controllability of the in-plane strain originated from the vacancy formation in Si-doped AlN (AlN:Si) and their interaction with edge dislocations. The strain state of the Si:AlN top interface could be well d...
We present a monolithically integrated extended cavity diode laser at 778 nm with a 3 dB linewidth of 200 kHz @ 1 ms. This is the first successful demonstration of active layer removal in AlGaAs by a 2-step epitaxy manufacturing process.
Recovery of epitaxial AlN films on sapphire at high temperatures is now an established process to produce pseudo-substrates with high crystalline perfection, which can be used to grow epitaxial structures for UV-light-emitting devices. To elucidate the elementary mechanisms taking place during the thermal treatment of MOVPE-grown films, we studied...
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 sub-micrometer range. Dark spots can significantly reduce the internal quantum efficiency in single layers, or whole (Al,Ga)N-...
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 related to CN and CN−Hi that decrease with increasing carbon concentration. Besides the formation of nonradiat...
A resonant-tunneling conductivity was experimentally registered in a doped heterostructure with a single quantum well using admittance spectroscopy. Earlier, this effect was only realized in artificially created resonant tunneling structures, having four heterojunctions. A heterostructure with an In0.3Ga0.7As/GaAs quantum well was examined in the t...
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 a peak wavelength of 233 nm, with a full width at half maximum...
On the example of epitaxial lateral overgrowth of AlN on trench-patterned AlN/sapphire templates the impact of introducing a high-temperature annealing step into the process chain is investigated. Covering the open surfaces of sapphire trench sidewalls with a thin layer of AlN is found to be necessary to preserve the trench shape during annealing....
We present a monolithic integrated passively Q-switched sub-150 ps microchip laser at 1064 nm with a wedged Nd:YVO4 crystal operating up to a repetition rate of 1 MHz. The wedge enables to change the cavity length by a small amount to fine tune the spectral cavity mode position over the full gain bandwidth of Nd:YVO4 and hence to optimize the outpu...
Light emitting diode structures emitting in the ultraviolet spectral range are investigated. The samples exhibit defect luminescence bands. Synchrotron-based photoluminescence excitation spectroscopy of the complicated multi-layer stacks is employed to assign the origin of the observed defect luminescence to certain layers. In the case of quantum w...
Light emitting diodes (LED) with an emission wavelength of 310 nm containing either a single or a triple quantum well are compared regarding their efficiency and long‐term stability. Additionally, the influence of the thickness of the lower quantum well barrier and the quantum well thickness in single quantum well (SQW) LEDs is investigated. Electr...
Abstract A multi‐active‐region bipolar‐cascade edge‐emitting laser emitting at nearly 900 nm is presented. The three active regions and two tunnel junctions located in a single waveguide core share the same third‐order vertical mode. A slope efficiency of 3.6 W/A was measured with a threshold current density of 230 A/cm2. The epitaxial layer stack...
The impact of different AlN/sapphire template technologies (i.e. planar, epitaxial lateral overgrown (ELO) and high temperature annealed sputtered ELO) is studied with respect to the operation-induced degradation of 265 nm UVC LEDs. UVC LEDs with identical heterostructures were grown on templates providing different threading dislocation densities...
The effect of high-temperature annealing (HTA) at 1700 °C on AlN films grown on 4H–SiC substrates by metalorganic vapor phase epitaxy has been studied. It is shown that the structural quality of the AlN layers improves significantly after HTA similar to what has been demonstrated for AlN grown on sapphire. Dislocation densities reduce by one order...
We developed a red to near infrared continuous tunable laser system seeded by a picosecond passively Q-switched microchip laser at 1064 nm. Pulse duration below 150 ps and pulse energy > 700 nJ with kHz repetition rate were achieved.
In the past few years, high‐temperature annealing of AlN has become a proven method for providing AlN layers with low dislocation densities. Herein, the example of Al0.77Ga0.23N is used to investigate whether annealing can also improve the material quality of the ternary alloy. A detailed analysis of the influence of annealing temperature on struct...
Solid state UV emitters have many advantages over conventional UV sources. The (Al,In,Ga)N material system is best suited to produce LEDs and laser diodes from 400 nm down to 210 nm—due to its large and tuneable direct band gap, n- and p-doping capability up to the largest bandgap material AlN and a growth and fabrication technology compatible with...
We present a monolithic integrated passively Q-switched sub-150 ps microchip laser at 1064 nm with a slightly wedged Nd:YVO4 crystal for fine tuning of the spectral cavity mode position relative to the gain profile to optimise the output power and to increase wafer scale mass production yield.
In this article we describe the scanning electron microscopy (SEM) techniques of electron channelling contrast imaging and electron backscatter diffraction. These techniques provide information on crystal structure, crystal misorientation, grain boundaries, strain and structural defects on length scales from tens of nanometres to tens of micrometre...
In this article we describe the scanning electron microscopy (SEM) techniques of electron channelling contrast imaging and electron backscatter diffraction. These techniques provide information on crystal structure, crystal misorientation, grain boundaries, strain and structural defects on length scales from tens of nanometres to tens of micrometre...
The effects of the design and thicknesses of different optically transparent p‐current spreading layers (short‐period superlattice, superlattice and bulk p‐Al0.38Ga0.62N) as well as the type and thickness of the p‐GaN cap layer on the electrical and optical characteristics of 310 nm ultraviolet light emitting diodes have been investigated. Scanning...
A bulk photovoltaic effect was observed in insulating carbon-doped gallium nitride crystals by investigating the light-induced change of the contact potential difference with a Kelvin probe as a function of the carbon concentration in the crystal. Bulk polarization was caused by excitation of defects setting in at photon energies of 0.95–1.05 eV (C...
P-type contacts with a high reflectivity in the ultraviolet spectral region made of molybdenum/aluminum (Mo/Al) on AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) emitting at 265 nm have been investigated. Optimized Mo/Al contacts are shown to have a high optical reflectivity above 75 % at 265 nm. DUV LEDs with an absorbing p-AlGaN he...
In this work, we investigate the impact of high‐temperature (HT) annealing on the crystalline structure of MOVPE‐grown boron‐containing AlN layers. High‐resolution X‐ray diffraction studies reveal AlBN in wurtzite configuration for non‐annealed 300nm thick layers containing several percent of boron. After 3h annealing at 1700°C, the AlBN‐related re...
Carbon doping is used to obtain semi-insulating GaN crystals. If the carbon doping concentration exceeds 5 × 10¹⁷ cm⁻³, the carbon atoms increasingly form triatomic clusters. The tri-carbon defect structure is unambiguously proven by the isotope effect on the defects' local vibrational modes (LVMs) originally found in samples containing carbon of n...
Non-intentionally doped c-plane GaN layers are generally employed as p-side waveguide layers in violet/blue-emitting laser diodes. The recombination and diffusion of charge carriers in the p-side GaN waveguide influence the injection efficiency of holes into the InGaN quantum wells of these devices. In this study, the non-radiative recombination an...
In this paper, the properties of Pd-based p-contacts on GaN-based laser diodes are discussed. Pd is often the metal of choice for ohmic contacts on p-GaN. However, for Pd/p-GaN ohmic contacts, nanovoids observed at the metal/semiconductor interface can have a negative impact on reliability and also reproducibility. The authors present a thorough an...
Strain relaxation mechanisms in AlGaN based light emitting diodes emitting in the ultraviolet B spectral range (UVB‐LEDs) grown on different AlN/sapphire templates are analyzed by combining in situ reflectivity and curvature data with transmission electron microscopy. In particular, the impact of dislocation density, surface morphology, and lattice...