Temperature-independent slow carrier emission from deep-level defects in p-type germanium

In the deep-level transient spectroscopy (DLTS) spectra of the 3d-transition metals cobalt and chromium in p-type germanium, evidence is obtained that hole emission from defect levels can occur by two parallel paths. Besides classical thermal emission, we observed a second, slower and temperature-independent emission. We show that this extra emission component allows determining unambiguously whether or not multiple DLTS peaks arise from the same defect. Despite similar characteristics, we demonstrate that the origin of the non-thermal emission is not tunnelling but photoionization related to black-body radiation from an insufficiently shielded part of the cryostat

Iron-boron pair dissociation in silicon under strong illumination

The dissociation of iron-boron pairs (FeB) in Czochralski silicon under strong illumination was investigated. It is found that the dissociation process shows a double exponential dependence on time. The first fast process is suggested to be caused by a positive Fe in FeB capturing two electrons and diffusion triggered by the electron-phonon interactions, while the second slow one would involve the capturing of one electron followed by temperature dependent dissociation with an activation energy of (0.21 +/- 0.03) eV. The results are important for understanding and controlling the behavior of FeB in concentrator solar cells

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

In situ UHVEM study of {113}-defect formation in Si nanowires

Results are presented of a study of {113}-defect formation in vertical Si nanowire n-type tunnel field effect transistors with nanowire diameters ranging from 40 to 500 nm. The nanowires are etched into an epitaxial moderately As doped n-type layer grown on a heavily As doped n(+) Si substrate. p(+) contacts on the nanowire are created by epitaxial growth of a heavily B doped layer. Using focused ion beam cutting, samples for irradiation are prepared with different thicknesses so that the nanowires are fully or partially embedded in the sample thickness. {113}-defects are created in situ by 2 MeV e-irradiation in an ultra-high voltage electron microscope between room temperature and 375 degrees C. The observations are discussed in the frame of intrinsic point defect properties, taking into account the role of dopants and capping layers. The important impact of the specimen thickness is elucidated