Role of Carbon on the electrical, optical and structural properties of GaN
Synthesis and Properties of Functional Materials
Final Report Abstract
The starting point of the project was to investigate the potential of carbon as a shallow acceptor in gallium nitride (GaN) grown by molecular beam epitaxy (MBE). MBE offers the possibility to establish ultra-pure GaN as a perfect clean reference system for further doping trials. Potential acceptor signatures of carbon were investigated in temperature-dependent transport and photoluminescence experiments, while its atom concentration was verified with element-specific analyses. It was found that at moderate level below 1e18cm-3 carbon- doping does not result in p-type conductivity below 300K. Nevertheless it was shown, that carbon is able to very well compensate unintentional donors in GaN. A prime example is the elimination of parasitic conductivity at the substrate/MBE interface originating from inherently present silicon at the wafer surface. This parasitic conductivity is detrimental for the performance of lateral devices, as it prevents e.g. switching-off of field-effect transistors (FETs), and can be compensated for by carbon when the layer stacks are grown on uncompensated substrates. Signatures of acceptor-bound excitons related to carbon in near band-gap emission spectra around 3.4eV could not be found in photoluminescence data at temperatures above 15K. Regardless of this fact, carbon in GaN contributes to yellow luminescence (YL), an emission band around 2.2eV originating from its deep acceptor character, which was and is in the focus of GaN research since many decades. Even in ultra- pure material with no traceable carbon impurity there also seems to exist a deep defect level, which contributes to YL and cannot be related to carbon. Band diagram simulations of GaN/AlGaN heterostructures as well as the switching characteristics of lateral FETs prove, that in a likely scenario this deep defect can pin the Fermi level in ultra-pure GaN deep inside the band-gap. These findings should trigger further experimental investigations on deep acceptor states in GaN.
Publications
- Carbon-doped MBE GaN: Spectroscopic Insights, Cryst. Growth 514, p. 29-35, 2019
D. Pohl, V.V. Solovyev, S. Röher, J. Gärtner, I.V. Kukushkin, T. Mikolajick, A. Großer, and S. Schmult, J.
(See online at https://doi.org/10.1016/j.jcrysgro.2019.02.041) - Critical parameters for the presence of a 2DEG in GaN/AlxGa1-xN heterostructures, AIP Advances 9, 125018, 2019
T. Scheinert, T. Mikolajick, and S. Schmult
(See online at https://doi.org/10.1063/1.5126917) - Magneto-optical Confirmation of Landau Level Splitting in a GaN/AlGaN 2DEG grown on Bulk GaN, J. Vac. Sci. Technol. B 37 (2), 021210, 2019
S. Schmult, V.V. Solovyev, S. Wirth, A. Großer, T. Mikolajick, and I.V. Kukushkin
(See online at https://doi.org/10.1116/1.5088927) - Heterostruktur einer elektronischen Schaltung mit einem Halbleiterbauelement, DE 10 2018 006 173, issued July 9, 2020
Stefan Schmult (TU Dresden), Andre Wachowiak (NaMLab gGmbH), Alexander Ruf (NaMLab gGmbH)
- Normally-off operation of lateral field-effect transistors fabricated from ultra-pure GaN/AlGaN heterostructures, Phys. Stat. Solidi a 217, 1900732, 2020
S. Schmult, S. Wirth, V.V. Solovyev, R. Hentschel, A. Wachowiak, T. Scheinert, A. Großer, I.V. Kukushkin and T. Mikolajick
(See online at https://doi.org/10.1002/pssa.201900732) - Quantum and transport lifetimes in optically-induced GaN/AlGaN 2DEGs grown on bulk GaN, J. Vac. Sci. Technol. B 38, 042203, 2020
Luisa Krückeberg, Steffen Wirth, Victor Solovyev, Andreas Großer, Igor Kukushkin, Thomas Mikolajick and Stefan Schmult, J.
(See online at https://doi.org/10.1116/1.5145198) - Light-tunable 2D subband population in a GaN/AlGaN heterostructure, Appl. Phys. Lett. 118 (1), 013101, 2021
V.V. Solovyev, S. Schmult, L. Krückeberg, A. Großer, T. Mikolajick, and I.V. Kukushkin
(See online at https://doi.org/10.1063/5.0027010)
