1. Laboratory of Semiconductor Materials, Institute of Materials, School of Engineering, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
2. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore
3. Laboratory of Thermomechanical Metallurgy, School of Engineering, Ecole Polytechnique Fédérale de Lausanne, 2002 Neuchâtel, Switzerland
4. Institute of Physics, School of Basic Sciences, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland