Juergen Christen

Juergen Christen
Otto-von-Guericke University Magdeburg | OvGU · Institute of Physics (IfP)

PhD

About

469
Publications
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12,694
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Publications

Publications (469)
Article
Selective area epitaxial growth is an important technique, both for monolithic device integration as well as for defect reduction in heteroepitaxy of crystalline materials on foreign substrates. While surface engineering with masking materials or by surface structuring is an effective means for controlling the location of material growth, as well a...
Article
Full-text available
Sputter epitaxy is a low cost process suited for the deposition of group‐III‐nitride semiconductors and allowing the deposition on large substrate areas at lower growth temperatures than in metalorganic vapour phase epitaxy (MOVPE). We demonstrate high quality AlN, AlGaN and GaN epitaxially grown on Si(111) substrates by reactive magnetron sputteri...
Article
Full-text available
We report on nanoscopic exploration of the luminescence from individual InP quantum dots (QDs) by means of highly spatially resolved cathodoluminescence (CL) spectroscopy directly performed in a scanning transmission electron microscope (STEM). A 7-fold layer stack with high-density InP quantum dots is embedded as an active medium membrane in an ex...
Article
Blue and yellow emission bands in carbon-doped GaN grown by MBE were investigated in low-temperature cathodoluminescence measurements performed in a scanning transmission electron microscope (STEM-CL) with high spatial resolution. Blue luminescence at 2.85 eV and two contributions in the spectral range of the yellow emission band around 2.2 eV sepa...
Article
Full-text available
We report on the formation process of GaN/AlN quantum dots which arises after the deposition of 1 - 2 monolayers of GaN on an AlN/sapphire template followed by a distinct growth interruption. The influence of the duration of a growth interruption on structural and optical properties of the GaN layer has been systematically investigated. Quantum dot...
Article
Full-text available
The characteristic energies of traps in InAlN/AlN/GaN high-electron mobility transistor structures on Si(111) substrates formed after irradiation with 75 MeV S-ions is studied by means of c-lattice parameter analysis, vertical IV-characteristics, micro-photoluminescence (µ-PL), photocurrent (PC) and thermally stimulated current (TSC) spectroscopy....
Article
Full-text available
We report on the realization of highly conductive and highly reflective n-type AlInN/GaN distributed Bragg reflectors (DBR) for use in vertical cavity surface emitters in a metalorganic vapor phase epitaxy process. While Ge-doping enables low-resistive n-type GaN/AlInN/GaN heterostructures, very high Ge doping levels compromise maximum optical refl...
Article
We present a pulsed reactive magnetron sputter process for high quality AlN on Si (111) beneficially avoiding any high-temperature growth. Initially, metallic aluminium with a nominal thickness of about one monolayer is deposited at a substrate temperature around 850 °C in an Ar plasma followed by sputtering in an Ar/N plasma. For 250 nm thick AlN...
Conference Paper
Full-text available
Freshly introduced a-screw dislocations in gallium nitride are an effective source of ultraviolet radiation, characterized by intense emission of narrow luminescence doublet lines in the spectral range of 3.1-3.2 eV. Furthermore, an additional narrow spectral line with an energy of 3.3 eV has been found at the points of intersection of such disloca...
Article
Full-text available
Color‐tunable InGaN/GaN multi‐quantum‐well (MQW) light‐emitting diodes (LEDs) are reported based on GaN microfacet structure directly grown on c‐plane patterned sapphire substrate by metal organic vapor phase epitaxy (MOVPE) through promoting 3D growth. By adjusting GaN growth temperature and pattern arrangement, a GaN microfacet with almost pure {...
Article
Full-text available
AlN/GaN/AlN quantum disks (Q-disks) embedded in self-assembled hexagonally shaped GaN nanowires have been grown on the Si (111) substrate by plasma-assisted molecular beam epitaxy. To correlate the structural and optical properties of individual Q-disks inside the nanowire, highly spatially resolved cathodoluminescence (CL) spectroscopy in a scanni...
Chapter
Microcavities with InGaN quantum wells or GaN-based quantum dots as active medium are building blocks of electrically-driven, low-threshold surface-emitting lasers or single photon emitters in the visible-to-UV spectral range. In this chapter, we highlight essential developments in epitaxial growth techniques of such nitride-based microcavities and...
Chapter
Advanced characterization methods with nanoscale resolution are powerful tools in order to overcome the continuing challenges in the optimization of nitride semiconductor nanostructures for more efficient nanophotonic devices in the UV and green spectral range. This chapter is devoted to the study of optical, electronic, and structural properties o...
Article
Investigating closely stacked GaN/AlN multiple quantum wells (MQWs) by means of cathodoluminescence spectroscopy directly performed in a scanning transmission electron microscope, we have reached an ultimate spatial resolution of σCL=1.8 nm. The pseudomorphically grown MQWs with high interface quality emit in the deep ultraviolet spectral range. De...
Article
Mapping individual radiative recombination channels at the nanoscale in direct correlation with the underlying crystal structure and composition of III–V semiconductor nanostructures requires unprecedented highly spatially resolved spectroscopy methods. Here, we report on a direct one-by-one correlation between the complex radial structure and the...
Article
AlInN/GaN heterostructure field effect transistors (HFETs) grown on silicon withstand irradiation with 75 MeV sulfur ions up to fluences of 5.5×10 13 ions/cm2. The static transistor operation characteristics of the devices exhibit a shift of the threshold voltage, a decrease in the saturation and off-state current. Micro-photoluminescence spectrosc...
Article
Ordered arrays of very high quality, defect-free GaN nanocolumns were achieved by selective area growth following a two step process involving nanopillar dry etching (top down) and overgrowth by Molecular Beam Epitaxy (bottom up). A study by transmission electron microscopy, over more than 50 individual nanocolumns, confirmed the absence of extende...
Article
Full-text available
An In 0.7 Ga 0.3 N layer with a thickness of 300 nm deposited on GaN/sapphire template by molecular beam epitaxy has been investigated by highly spatially resolved cathodoluminescence (CL). High crystal film quality without phase separation has been achieved. The InGaN layer shows intense emission in the IR spectral region. The lateral as well as t...
Article
Full-text available
Higher indium incorporation in self-organized triangular nanoprisms at the edges of InGaN/GaN core-shell nanorods is directly evidenced by spectral cathodoluminescence microscopy in a scanning transmission electron microscope. The nanoprisms are terminated by three 46 nm wide a-plane nanofacets with sharp interfaces forming a well-defined equilater...
Article
Full-text available
The structural and optical properties of InGaSb/GaP(001) type‐II quantum dots (QDs) grown by metalorganic vapor phase epitaxy (MOVPE) are studied. Growth strategies as growth interruption (GRI) after deposition of InGaSb and Sb‐flush prior to QD growth are used to tune the structural and optical properties of InGaSb QDs. The Sb‐flush affects the su...
Article
Full-text available
Despite the strong interest in optoelectronic devices working in the deep ultraviolet range, no suitable low cost, large-area, high-quality AlN substrates are available up to now. The aim of this work is the selective area growth of AlN nanocolumns by plasma assisted molecular beam epitaxy on polar (0001) and semi-polar (11-22) GaN/sapphire templat...
Article
Quantitative STEM: Comparative Studies of Composition and Optical Properties of Semiconductor Quantum Structures - Volume 23 Issue S1 - Andreas Rosenauer, Florian Fritz Krause, Knut Müller-Caspary, Elias Goldmann, Frank Jahnke, Matthias Paul, Michael Jetter, Peter Michler, Marcus Müller, Peter Veit, Jürgen Christen, Tilman Schimpke, Jan-Philipp Ahl...
Article
Full-text available
Nanometer-scale Resolved Cathodoluminescence Imaging: New Insights into GaAs/AlGaAs Core-shell Nanowire Lasers - Volume 23 Issue S1 - Marcus Müller, Peter Veit, Bernhard Loitsch, Julia Winnerl, Sonja Matich, Frank Bertram, Gregor Koblmüller, Jonathan J. Finley, Jürgen Christen
Preprint
A pencil-like morphology of homoepitaxially grown GaN nanowires is exploited for the fabrication of thin conformal intrawire InGaN nanoshells which host quantum dots in nonpolar, semipolar and polar crystal regions. All three quantum dot types exhibit single photon emission with narrow emission line widths and high degrees of linear optical polariz...
Preprint
Single-photon emitters (SPEs) are at the basis of many applications for quantum information management. Semiconductor-based SPEs are best suited for practical implementations because of high design flexibility, scalability and integration potential in practical devices. Single-photon emission from ordered arrays of InGaN nano-disks embedded in GaN...
Article
Full-text available
We investigate the emission from confined excitons in the structure of a single-monolayer-thick quasi-two-dimensional (quasi-2D) InxGa1−xN layer inserted in GaN matrix. This quasi-2D InGaN layer was successfully achieved by molecular beam epitaxy (MBE), and an excellent in-plane uniformity in this layer was confirmed by cathodoluminescence mapping...
Article
Semipolar orientations of GaN have attracted considerable attention as potential platforms for high brightness light-emitting devices. The heteroepitaxy of semipolar GaN layers results in high densities of threading dislocations (TDs) and basal-plane stacking faults (BSFs). Various defect reduction methods have been employed to improve the crystal...
Article
This work reports on compositionally graded N-polar InxGa1-xN layers. The InGaN grades with different final In compositions up to were grown by plasma-assisted molecular beam epitaxy on vicinal GaN base layers with a miscut angle of 4° towards the m-direction. When increasing the surface morphology evolved from an interlacing finger structure, attr...
Article
A pencil-like morphology of homoepitaxially grown GaN nanowires is exploited for the fabrication of thin conformal intra-wire InGaN nanoshells which host quantum dots in nonpolar, semipolar and polar crystal regions. All three quantum dot types exhibit single photon emission with narrow emission linewidths and high degrees of linear optical polariz...
Chapter
The image intensity in high-angle annular dark field STEM images shows a strong chemical sensitivity. As it is also influenced by specimen thickness, crystal orientation as well as characteristics of illumination and detector, a standard-free quantification of composition requires a comparison with accurate image simulation, for which we use the fr...
Poster
Self‐assembled nanocolumns (NCs) with InGaN/GaN disks constitute an alternative to conventional light emitting diodes (LED) planar devices [1]. However, their efficiency and reliability are hindered by a strong dispersion of electrical characteristics among individual nanoLED. Polychromatic emission derives from an inhomogeneous distribution of ind...
Article
Nitride-based three-dimensional core-shell nanorods (NRs) are promising candidates for the achievement of highly efficient optoelectronic devices. For a detailed understanding of the complex core-shell layer structure of InGaN/GaN NRs, a systematic determination and correlation of the structural, compositional, and optical properties on a nanometer...
Article
Full-text available
div class="title">Nanoscale Imaging of Structural and Optical Properties Using Helium Temperature Scanning Transmission Electron Microscopy Cathodoluminescence of Nitride Based Nanostructures - Volume 22 Issue S3 - Frank Bertram, Marcus Müller, Gordon Schmidt, Peter Veit, Silke Petzold, Steven Albert, Ana María Bengoechea-Encabo, Miguel Ángel Sánch...
Article
div class="title">Nanoscale Cathodoluminescence of an InGaN Single Quantum Well Intersected by Individual Dislocations - Volume 22 Issue S3 - Gordon Schmidt, Peter Veit, Sebastian Metzner, Christoph Berger, Frank Bertram, Armin Dadgar, Andre Strittmatter, Jurgen Christen
Article
Full-text available
Crystal phase quantum dots (CPQD) embedded in a nanowire (NW) geometry have recently emerged as efficient single photon emitters. In typical III–V semiconductor NWs such CPQDs are linked to the well-known zincblende (ZB)/wurtzite (WZ) polytypism that occurs mostly randomly along the NW axis, making it difficult to assess the exact position and micr...
Conference Paper
In this contribution we present our recently developed “reverse-reaction-growth” scheme in molecular beam epitaxy to fabricate 1D GaAs nanowires (NWs) with diameters down to 7 nm. We observe the presence of strong quantum confinement phenomena, opening the path towards a true 1D NW platform. The introduction of crystal defects in the NW effectively...
Article
Large arrays of GaN core–shell microrods were fabricated on Si(111) substrates applying a combined bottom-up and top-down approach which includes inductively coupled plasma (ICP) etching of patterned GaN films grown by metal–organic vapor phase epitaxy (MOVPE) and selective overgrowth of obtained GaN/Si pillars using hydride vapor phase epitaxy (HV...
Article
We give direct evidence of distinct quantum dot states clustered but also spatially separated in single GaN islands. Resulting from GaN layer growth on top of AlN, the islands are predominantly formed in close vicinity to threading dislocation bundles. Detailed analysis of the inner optical and structural properties, performed by nanoscale cathodol...
Article
Three-dimensional (3D) InGaN/GaN quantum-well (QW) core–shell light emitting diodes (LEDs) are a promising candidate for the future solid state lighting. In this contribution, we study direct correlations of structural and optical properties of the core–shell LEDs using highly spatially-resolved cathodoluminescence spectroscopy (CL) in combination...
Article
Among the major obstacles for development of non-polar and semipolar GaN structures on foreign substrates are stacking faults which deteriorate the structural and optical quality of the material. In this work, an in-situ SiNx nano-network has been employed to achieve high quality heteroepitaxial semipolar (112¯2)GaN on m-plane sapphire with reduced...
Article
This work reports an experimental and theoretical insight into phenomena of two-color emission and different electron-hole recombination dynamics in InGaN nanodisks, incorporated into pencil-like GaN nanowires. The studied nanodisks consist of one polar (on c facet) and six (nominally) identical semipolar (on r facets) sections, as confirmed by tra...
Article
A uniform array of gallium nitride core‐shell microrod (MR) light‐emitting diode (LED) structures was grown by metalorganic vapor phase epitaxy. Defects and the quantum well (QW) luminescence in an individual rod were investigated by scanning tunneling electron microscopy (STEM) and STEM cathodoluminescence. Luminescence with different wavelength w...
Article
We report on metalorganic vapor phase epitaxy (MOVPE) of distributed Bragg reflectors (DBR) applying a periodic modulation of the GaN doping concentration only. The doping modulation changes the refractive index of GaN via the Burstein-Moss-effect. MOVPE growth of highly doped GaN:Ge and modulation of the dopant concentration by at least two orders...
Article
authoren We report the growth of green emitting InGaN quantum wells (QWs) by metal-organic vapor-phase epitaxy (MOVPE) on three-dimensional GaN templates. The {10overbar11} facets of GaN pyramids, fabricated by selective-area growth (SAG), reduce the influence of the quantum-confined Stark effect (QCSE) on the emission properties of the QW. The lum...
Article
Spatially resolved cathodoluminescence (CL) microscopy is used to study semipolar {112-2} gallium nitride (GaN) grown out of trenches with c-plane-like sidewalls etched into the r-plane {11-02} sapphire substrate. The beneficial effect of growing locally c-GaN on c-sapphire and subsequent switching to the semipolar growth mode manifests in bending...
Article
Polarization-field reduction in c-plane InGaN multi-quantum well (MQW) structures is achieved by pulsed-flow growth of quaternary AlInGaN barriers using metalorganic vapor phase epitaxy (MOVPE). The pulsed-flow growth allows for precise control of the quaternary composition at very low growth rate. In photoluminescence (PL) experiments a blue-shift...
Article
The optical and crystalline properties of a c-plane GaN-based LED structure with embedded semipolar InGaN quantum wells (QW) were investigated using highly spatially resolved cathodoluminescence spectroscopy (CL) directly performed in a scanning transmission electron microscope (STEM). Direct correlation of the cross-sectional STEM image with the s...
Article
In GaN, the basal plane stacking fault type I1 is a two-dimensional defect characterized by a cubic inclusion within the wurtzite structure. Excitons are bound at the BSF I1 similar to the localization in a quantum well heterostructure leading to an efficient radiative recombination. In this study, we present the optical and structural properties o...
Conference Paper
In the past few years, tremendous progress has been achieved on epitaxial growth and processing of group III nitride nano- and microrods. Furthermore, these growth improvements have allowed the fabrication of optoelectronic devices based nanorods as active elements, i.e. light emitting diodes (LEDs). However, their efficiency is still far behind th...
Article
Full-text available
Single-photon emitters (SPEs) are at the basis of many applications for quantum information management. Semiconductor-based SPEs are best suited for practical implementations because of high design flexibility, scalability and integration potential in practical devices. Single-photon emission from ordered arrays of InGaN nano-disks embedded in GaN...
Article
GaN based laser diodes with semipolar quantum wells are typically grown on free-standing pseudo-substrates of small size. We present an approach to create a distributed-feedback (DFB) laser with semipolar quantum wells (QWs) on c-oriented templates. The templates are based on 2-inch sapphire wafers, the method could easily be adapted to larger diam...
Article
Selective area growth has been applied to fabricate a homogeneous array of GaN nanocolumns (NC) with high crystal quality. The structural and optical properties of single NCs have been investigated at the nanometer-scale by transmission electron microscopy (TEM) and highly spatially resolved cathodoluminescence (CL) spectroscopy performed in a scan...
Article
Full-text available
Intense emission from GaN islands embedded in AlN resulting from GaN/AlN quantum well growth is directly resolved by performing cathodoluminescence spectroscopy in a scanning transmission electron microscope. Line widths down to 440 μeV are measured in a wavelength region between 220 and 310 nm confirming quantum dot like electronic properties in t...
Article
The gallium gradient in Cu(In,Ga)Se2 (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co-evaporation processes, plays a key role in the device performance of CIGS thin-film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradie...
Conference Paper
Full-text available
Enhancement of optical and structural quality of semipolar (1122) GaN grown by metal-organic chemical vapor deposition on planar m-sapphire substrates was achieved by using an in situ epitaxial lateral overgrowth technique with nanoporous SiNx layers employed as masks. The effect of SiNx deposition time on optical and structural quality of the film...
Conference Paper
Full-text available
Reduced electric field in semipolar (1122) GaN/InGaN heterostructures makes this orientation attractive for high efficiency light emitting diodes. In this work, we investigated indium incorporation in semipolar (1122) GaN grown by metal-organic chemical vapor deposition on planar m-plane sapphire substrates. Indium content in the semipolar material...
Article
A 5λ-thick hybrid semiconductor/dielectric GaN-based microcavity grown by metal-organic chemical vapor deposition on a c-plane bulk GaN substrate was investigated using angle-resolved photoluminescence and angle-resolved cathodoluminescence techniques at room and low temperature (5.8 K), respectively. The cavity structure consisted of an InGaN mult...
Conference Paper
Full-text available
The realization of reliable single photon emitters operating at high temperature and located at predetermined positions still presents a major challenge for the development of solid-state systems for quantum light applications. We demonstrate single-photon emission from two-dimensional ordered arrays of GaN nanowires containing InGaN nanodisks. The...
Article
We report the influence of {111} stacking faults on the cathodoluminescence (CL) emission characteristics of cubic GaN (c-GaN) films and cubic GaN/AlN multi-quantum wells. Transmission electron microscopy (TEM) measurements indicate that stacking faults (SFs) on the {111} planes are the predominant crystallographic defects in epitaxial films, which...
Conference Paper
Full-text available
The realization of reliable single photon emitters operating at high temperature and located at predetermined positions still presents a major challenge for the development of solid-state systems for quantum light applications. We demonstrate single-photon emission from two-dimensional ordered arrays of GaN nanowires containing InGaN nano-disks. Th...
Article
Full-text available
Diffusion lengths of photo-excited carriers along the c-direction were determined from photoluminescence (PL) and cross-sectional cathodoluminescence (CL) measurements in p- and n-type GaN epitaxial layers grown on c-plane sapphire by metal-organic chemical vapor deposition. The investigated samples incorporate a 6 nm thick In0.15Ga0.85N active lay...
Article
Full-text available
In this contribution we report on the optical properties of cubic AIN/GaN asymmetric multi quantum wells (MQW) structures on 3C-SiC/Si (001) substrates grown by radio-frequency plasma-assisted molecular beam epitaxy (MBE). Scanning transmission electron microscopy (STEM) and spatially resolved cathodoluminescence (CL) at room temperature and at low...
Article
The technique of time-of-flight cathodoluminescence measurements of semi-conductive samples is covered by a lightproof mask with a special geometry. The results of experimental measurements of cathodoluminescence transient for bulk samples of gallium nitride in a wide temperature range (5-300 K) are shown. The results based on the analysis of the m...
Article
A comprehensive study on the impact of growth modes on the structural and optical properties of thick InGaN layers suitable for photovoltaic application is presented. Samples grown by metalorganic vapour phase epitaxy with different growth rates and thicknesses have been analyzed. The application of slow growth rates result in smooth layers while h...
Article
Full-text available
Using cathodoluminescence spectroscopy directly performed in a scanning transmission electron microscope at liquid helium temperatures, the optical and structural properties of a 62 InGaN/GaN multiple quantum well embedded in an AlInN/GaN based microcavity are investigated at the nanometer scale. We are able to spatially resolve a spectral redshift...