DLTS and FTIR study of quenching induced defects in germanium

Due to the high carrier mobility in Ge, it is more and more used as active semiconducting layer in advanced electronic devices on Si substrates [1]. Successful growth, doping and further processing of Ge requires however a good understanding of the intrinsic point defect properties that are unfortunately not well known. The present paper reports on the progress of an effort to determine the formation energy and diffusivity of the vacancy in Ge using thermal quenching techniques [2]. Experimental data on the thermal equilibrium concentration and diffusivity of vacancies in Ge are scarce and most are more than 40 years old. Most of the experimental data were obtained based on thermal quenching experiments assuming that the formed acceptors are due to quenched-in vacancies so that their concentration and formation energy can be determined from measured resistivity changes. The formation energy of the vacancy in its different charge states has recently also been calculated using ab initio calculations which showed that the (double) negatively charged vacancy has the lowest formation energy of about 2 eV in good agreement with the acceptor formation energy determined from the quenching experiments. Based on vacancy mediated dopant diffusion studies, Brotzmann et al [3] also concluded that the double negatively charged vacancy is the most probable charge state of the vacancy. In this contribution, the quenched-in acceptors are studied using deep-level transient spectroscopy. As Cu is known as contaminant which is difficult to avoid when quenching Ge, the electric properties of the quenched-in acceptors are carefully compared with those of substitutional Cu. Although at first glance similarities are striking, remarkable differences are also observed and discussed. [1] J. Vanhellemont and E. Simoen, J. Electrochem. Soc. 154 (2007), p. H572. [2] J. Vanhellemont, J. Lauwaert, A. Witecka, P. Spiewak, I. Romandic and P. Clauws, Physica B 404 (2009), p. 4529. [3] S. Brotzmann and H. Bracht, J. Appl. Phys. 103 (2008), p. 033508