Filters

2020 - 20212

More filters

2021 - 20222
Reset filters

Settings

Author: Hagedorn, Sylvia × DDC: 530 × Publisher: Weinheim : Wiley-VCH × WGL Institute: IKZ ×

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    High-Temperature Annealing of AlGaN
    (Weinheim : Wiley-VCH, 2020) Hagedorn, Sylvia; Khan, Taimoor; Netzel, Carsten; Hartmann, Carsten; Walde, Sebastian; Weyers, Markus
    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 structural and optical material properties is presented. It is found that with increasing annealing temperature, the threading dislocation density can be lowered from an initial value of 6.0 × 109 down to 2.6 × 109 cm−2. Ga depletion at the AlGaN surface and Ga diffusion into the AlN buffer layer are observed. After annealing, the defect luminescence between 3 and 4 eV is increased, accompanied by an increase in the oxygen concentration by about two orders of magnitude. Furthermore, due to annealing optical absorption at 325 nm (3.8 eV) occurs, which increases with increasing annealing temperature. It is assumed that the reason for this decrease in ultraviolet (UV) transmittance is the increasing number of vacancies caused by the removal of group-III and N atoms from the AlGaN lattice during annealing.
  • Thumbnail Image
    Item
    High‐Temperature Annealing and Patterned AlN/Sapphire Interfaces
    (Weinheim : Wiley-VCH, 2021) Hagedorn, Sylvia; Mogilatenko, Anna; Walde, Sebastian; Pacak, Daniel; Weinrich, Jonas; Hartmann, Carsten; Weyers, Markus
    Using 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. Both the influence of annealing temperature and annealing duration are investigated. To avoid the deformation of the AlN/sapphire interface during annealing, the annealing duration or annealing temperature must be low enough. Annealing for 1 h at 1730 °C is found to allow for the lowest threading dislocation density of 3.5 × 108 cm−2 in the subsequently grown AlN, while maintaining an uncracked smooth surface over the entire 2 in. wafer. Transmission electron microscopy study confirms the defect reduction by high-temperature annealing and reveals an additional strain relaxation mechanism by accumulation of horizontal dislocation lines at the interface between annealed and nonannealed AlN. By applying a second annealing step, the dislocation density can be further reduced to 2.5 × 108 cm−2.