LayTec is happy to announce the sale of an EpiCurveTT system to the Technical University of Braunschweig, Germany. The tool will be used by the group of Prof. A. Hangleiter for R&D of GaN based long wavelength emitters, mainly green lasers and LEDs.
Fig. 1:
a model of the wafer bow
process due to growing
In content: composition
induced lattice mismatch
causes wafer bow and
temperature deviations.
Dr. Uwe Rossow will use EpiCurve TT for monitoring and understanding the strain effects and the relaxation process of the underlying cladding and waveguide layers as well as of the layers in the active region of the emitting structures. His team uses Indium-Gallium-Nitride as quantum wells. EpiCurve TT measures in-situ wafer bowing, temperature and reflectance, which helps to control the stress, film composition, surface roughness and wafer temperature.
Fig. 1 shows roughly what happens when strained InGaN is grown on a GaN buffer: a layer of InGaN, which has a lattice constant larger than the underlying layer, forces the whole stack to bow. The wafer becomes convex, which causes temperature deviations in the middle and on the edges of the structure. Fig. 2 is an example of curvature measurements during growth of ternary InGaN and AlGaN layer. Both, film composition and strain induced relaxation can be detected.
"Simultaneous curvature and temperature measurements by EpiCurveTT already during the process will help us to control the relaxation process, to achieve better uniformity, to reproduce growth conditions and improve the structure quality," said Dr. Uwe Rossow. LayTec is looking forward to a successful collaboration with the University of Braunschweig!