Positron annihilation study of equilibrium point defects in GaAs Dissertation zur Erlangung des akademischen Grades Dr. rerum naturlalium (Dr. rer. nat.) vorgelegt der Mathematisch-Naturwissenschaftlich-Technischen Fakultät (mathematisch-naturwissenschaftlicher Bereich) der Martin-Luther-Universität Halle-Wittenberg von Herrn Vladimir Bondarenko geb. am 15.02.1978 in Sumy, Ukraine Gutachter: (1) Prof. Dr. R. Krause-Rehberg (2) Prof. Dr. U. M. Gösele (3) Prof. Dr. P. Masher urn:nbn:de:gbv:3-000006446[http://nbn-resolving.de/urn/resolver.pl?urn=nbn%3Ade%3Agbv%3A3-000006446] Halle(Saale), November 2003verteidigt am 30.01.2004 Table of contents 1.Introduction ____________________________________________________1 2. Thermodynamics of native point defects in GaAs_____________________3 2.1 GaAs system at melting point _____________________________________3 2.2 Defects chemistry in GaAs________________________________________5 2.3 Tan model and Fermi-level effect __________________________________7 2.4 Quantum mechanical calculations _________________________________9 2.5 Electrical compensation in n-type GaAs ___________________________11 3. Experimental methods _________________________________________13 3.1 Positron annihilation lifetime spectroscopy _________________________13 3.1.1 Physical background of positron trapping ________________________________ 13 3.1.