Browsing by Author "Hagedorn, S."
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- ItemAdvances in electron channelling contrast imaging and electron backscatter diffraction for imaging and analysis of structural defects in the scanning electron microscope(London [u.a.] : Institute of Physics, 2020) Trager-Cowan, C.; Alasmari, A.; Avis, W.; Bruckbauer, J.; Edwards, P.R.; Hourahine, B.; Kraeusel, S.; Kusch, G.; Jablon, B.M.; Johnston, R.; Martin, R.W.; Mcdermott, R.; Naresh-Kumar, G.; Nouf-Allehiani, M.; Pascal, E.; Thomson, D.; Vespucci, S.; Mingard, K.; Parbrook, P.J.; Smith, M.D.; Enslin, J.; Mehnke, F.; Kneissl, M.; Kuhn, C.; Wernicke, T.; Knauer, A.; Hagedorn, S.; Walde, S.; Weyers, M.; Coulon, P.-M.; Shields, P.A.; Zhang, Y.; Jiu, L.; Gong, Y.; Smith, R.M.; Wang, T.; Winkelmann, A.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 micrometres. Here we report on the imaging and analysis of dislocations and sub-grains in nitride semiconductor thin films (GaN and AlN) and tungsten carbide-cobalt (WC-Co) hard metals. Our aim is to illustrate the capability of these techniques for investigating structural defects in the SEM and the benefits of combining these diffraction-based imaging techniques.
- ItemHigh-temperature annealing of AlN films grown on 4H-SiC(New York, NY : American Inst. of Physics, 2020) Brunner, F.; Cancellara, L.; Hagedorn, S.; Albrecht, M.; Weyers, M.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 of magnitude resulting in 8 × 108 cm-2 for a-type and 1 × 108 cm-2 for c-type dislocations. The high-temperature treatment removes pits from the surface by dissolving nanotubes and dislocations in the material. XRD measurements prove that the residual strain in AlN/4H-SiC is further relaxed after annealing. AlN films grown at higher temperature resulting in a lower as-grown defect density show only a marginal reduction in dislocation density after annealing. Secondary ion mass spectrometry investigation of impurity concentrations reveals an increase of Si after HTA probably due to in-diffusion from the SiC substrate. However, C concentration reduces considerably with HTA that points to an efficient carbon removal process (i.e., CO formation). © 2020 Author(s).
- ItemOrigin of a-plane (Al,Ga)N formation on patterned c-plane AIN/sapphire templates(Milton Park : Taylor & Francis, 2013) Mogilatenko, A.; Kirmse, H.; Hagedorn, S.; Richter, E.; Zeimer, U.; Weyers, M.; Tränkle, G.a-plane (Al,Ga)N layers can be grown on patterned c-plane AlN/sapphire templates with a ridge direction along [1bar 100]Al2O3. Scanning nanobeam diffraction reveals that the formation of a-plane layers can be explained by nucleation of c-plane (Al,Ga)N with [11bar 20](Al,Ga)N
- ItemStrain induced power enhancement of far-UVC LEDs on high temperature annealed AlN templates(Melville, NY : American Inst. of Physics, 2023) Knauer, A.; Kolbe, T.; Hagedorn, S.; Hoepfner, J.; Guttmann, M.; Cho, H.K.; Rass, J.; Ruschel, J.; Einfeldt, S.; Kneissl, M.; Weyers, M.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 these templates. This mismatch introduces additional compressive strain in AlGaN quantum wells resulting in enhanced transverse electric polarization of the quantum well emission at wavelengths below 235 nm compared to layer structures deposited on conventional MOVPE-grown AlN templates, which exhibit mainly transverse magnetic polarized emission. In addition, high temperature annealed AlN/sapphire templates also feature reduced defect densities leading to reduced non-radiative recombination. Based on these two factors, i.e., better outcoupling efficiency of the transverse electric polarized light and an enhanced internal quantum efficiency, the performance characteristic of far-UVC LEDs emitting at 231 nm was further improved with a cw optical output power of 3.5 mW at 150 mA.
- ItemStructural and luminescence imaging and characterisation of semiconductors in the scanning electron microscope(Bristol : IOP Publ., 2020) Trager-Cowan, C.; Alasmari, A.; Avis, W.; Bruckbauer, J.; Edwards, P.R.; Ferenczi, G.; Hourahine, B.; Kotzai, A.; Kraeusel, S.; Kusch, G.; Martin, R.W.; McDermott, R.; Naresh-Kumar, G.; Nouf-Allehiani, M.; Pascal, E.; Thomson, D.; Vespucci, S.; Smith, M.D.; Parbrook, P.J.; Enslin, J.; Mehnke, F.; Kuhn, C.; Wernicke, T.; Kneissl, M.; Hagedorn, S.; Knauer, A.; Walde, S.; Weyers, M.; Coulon, P.-M.; Shields, P.A.; Bai, J.; Gong, Y.; Jiu, L.; Zhang, Y.; Smith, R.M.; Wang, T.; Winkelmann, A.The scanning electron microscopy techniques of electron backscatter diffraction (EBSD), electron channelling contrast imaging (ECCI) and cathodoluminescence (CL) hyperspectral imaging provide complementary information on the structural and luminescence properties of materials rapidly and non-destructively, with a spatial resolution of tens of nanometres. EBSD provides crystal orientation, crystal phase and strain analysis, whilst ECCI is used to determine the planar distribution of extended defects over a large area of a given sample. CL reveals the influence of crystal structure, composition and strain on intrinsic luminescence and/or reveals defect-related luminescence. Dark features are also observed in CL images where carrier recombination at defects is non-radiative. The combination of these techniques is a powerful approach to clarifying the role of crystallography and extended defects on a material's light emission properties. Here we describe the EBSD, ECCI and CL techniques and illustrate their use for investigating the structural and light emitting properties of UV-emitting nitride semiconductor structures. We discuss our investigations of the type, density and distribution of defects in GaN, AlN and AlGaN thin films and also discuss the determination of the polarity of GaN nanowires. © 2020 The Author(s). Published by IOP Publishing Ltd.