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27 results on '"Gaubas, E"'

4. Pulsed photo-ionization spectroscopy in carbon doped MOCVD GaN epi-layers on Si.

Author

Gaubas, E, Ceponis, T, Mickevicius, J, Pavlov, J, Rumbauskas, V, Velicka, M, Simoen, E, and Zhao, M

Subjects
*HETEROJUNCTION field effect transistors, *OPTICAL measurements, *CHEMICAL vapor deposition, *INDIUM gallium zinc oxide, *CRYSTAL defects, *CARRIER density, *DOPING agents (Chemistry)
Abstract

GaN with intentionally incorporated carbon to create semi-insulating buffer layers shows improved performance in AlGaN/GaN heterojunction field effect transistors. Moreover, various impurities and crystal imperfections of GaN epi-layers determine a rather rich spectrum of deep levels. Thus, spectroscopy of defects is of paramount importance in optimizing GaN-based devices. In this work, pulsed photo-ionization spectroscopy (PPIS) has been applied to trace the prevailing defects and simultaneously monitor variations of carrier lifetime in metal−organic chemical vapor deposition grown GaN epi-layers on Si substrates of various carbon content concentration. A contactless technique for microwave probed photoconductivity has been employed to measure changes in excess carrier density, in order to evaluate variations in carrier lifetime and reveal the type of photo-activation processes. Six PPI spectral steps have been resolved in samples containing either superlattices (SLs) or AlN/AlGaN stress management layers. Three of these centres, namely, and (CNON)0, have been associated with carbon dopants. Other PPIS peaks have been ascribed to Ga vacancies and metal impurities. It has been deduced from analysis of the PPIS peak broadening factor that rather strong electron−phonon coupling is inherent in photo-ionization of carbon related complexes at room temperature. The concentration of separated defects and cross-sections for photon−electron coupling have been determined using calibration measurements of optical transmittance spectra and correlations between microwave probed photoconductivity peak signals and absorption coefficient. [ABSTRACT FROM AUTHOR]

Published
2020
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8. Study of neutron irradiated structures of ammonothermal GaN

Author

Gaubas, E, primary, Ceponis, T, additional, Deveikis, L, additional, Meskauskaite, D, additional, Miasojedovas, S, additional, Mickevicius, J, additional, Pavlov, J, additional, Pukas, K, additional, Vaitkus, J, additional, Velicka, M, additional, Zajac, M, additional, and Kucharski, R, additional

Published
2017
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27. Comparative Study of Carrier Lifetime Dependence on Dopant Concentration in Silicon and Germanium.

Author

Gaubas, E. and Vanhellemont, J.

Subjects
COMPARATIVE studies, GERMANIUM, SILICON, DOPED semiconductors, RECOMBINATION in semiconductors, ELECTRONIC equipment, ELECTRONIC excitation, ELECTRIC conductivity, SOLID state electronics
Abstract

The increasing use of thin germanium layers on silicon substrates as active layers in advanced electronic devices is the motivation for a comparative study of the dependence of the carrier recombination characteristics on excitation and dopant concentration in both semiconductors. Bulk and surface components of the carrier lifetime are separated by studying samples with different geometries and surface finishing. The bulk carrier lifetime is determined as a function of dopant concentration and in the case of germanium also as a function of the excitation level. The bulk lifetime observations are simulated by combining the lifetime according to Shockley-Read-Hall (SRH) theory with the lifetime resulting from Auger recombination above a doping concentration threshold. It is shown that the bulk carrier lifetime behavior in Si and Ge is very similar. Carrier lifetime changes in Si can be well described by a combined SRH and Auger recombination model, while lifetime variations in Ge fit well the SRH model, taking into account the lifetime dependence on the injection level. It is shown that the lifetime dependence on dopant concentration in germanium can be phenomenologically described by assuming a linear increase of recombination center concentration with dopant concentration. The results also illustrate the importance of surface passivation and of material quality which depends on the fabrication technology, when comparing carrier lifetimes obtained with different equipment and on different samples. [ABSTRACT FROM AUTHOR]

Published
2007
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