Contact-free investigation of the EL2-defect in the surface of GaAs wafers B. Gründig-Wendrock, K. Dornich, T. Hahn, U. Kretzer and J. R. Niklas Eur. Phys. J. Appl. Phys., 27 1-3 (2004) 363-366 Published online: 15 July 2004 DOI: 10.1051/epjap:2004111