New wide-gap semiconductor materials for opto-electronics and for fundamental research
Final Report Abstract
Within the project novel aspects of GaN-based UV-sensitive and normally-off device concepts were investigated. Depending on the residual impurity background a 2DEG can be absent in dark environment in ultra-pure GaN/AlGaN stacks grown by MBE. This property facilitates the fabrication of normally-off lateral FETs. Additionally it represents a new class of UV-sensitive GaN-based devices, as a 2DEG can be generated optically. Low-temperature magnetotransport investigations reveal, that quantum transport and the 2DEG mobility is limited by elastic scattering events in these optically-generated 2DEGs. Scattering results from a yet unidentified deep acceptor not related to carbon, which was energetically identified and only varies by ~ 120 meV in energy compared to the energy of carbon. This also implies that the low temperature 2DEG mobility is not limited by the density of charged threading dislocations, as commonly reported in the past. By systematically varying the GaN/AlGaN layer stack architecture it was possible to achieve low 2D channel densities, desired for fundamental investigations of GaN/AlGaN based 2DEGs within the quantum Hall regime. Furthermore the role of atmospheric silicon adhesion at GaN substrate surfaces prior to overgrowth was examined. It turns out, that exposure of the GaN substrates to cleanroom environment leads to a silicon-induced parasitic channel the regrowth (substrate/MBE) interface, which deteriorates the operation of lateral field-effect devices and quantum transport behavior. It was shown that by compensating the silicon at the GaN substrate surface by carbon, the parasitic channel vanishes at low temperature and the undistorted 2DEG properties come to light.
Publications
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Quantum and transport lifetimes in optically induced GaN/AlGaN 2DEGs grown on bulk GaN. Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 38(4).
Krückeberg, Luisa; Wirth, Steffen; Solovyev, Victor V.; Großer, Andreas; Kukushkin, Igor V.; Mikolajick, Thomas & Schmult, Stefan
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Light-tunable 2D subband population in a GaN/AlGaN heterostructure. Applied Physics Letters, 118(1).
Solovyev, V. V.; Schmult, S.; Krückeberg, L.; Großer, A.; Mikolajick, T. & Kukushkin, I. V.
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Correlating yellow and blue luminescence with carbon doping in GaN. Journal of Crystal Growth, 586, 126634.
Schmult, S.; Schürmann, H.; Schmidt, G.; Veit, P.; Bertram, F.; Christen, J.; Großer, A. & Mikolajick, T.
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Spin-Orbit Interaction in GaN / Alx Ga1−x N Heterojunctions Probed by Electron Spin Resonance. Physical Review Applied, 18(2).
Shchepetilnikov, A.V.; Khisameeva, A.R.; Solovyev, V.V.; Großer, A.; Mikolajick, T.; Schmult, S. & Kukushkin, I.V.
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Status of Aluminum Oxide Gate Dielectric Technology for Insulated-Gate GaN-Based Devices. Materials, 15(3), 791.
Calzolaro, Anthony; Mikolajick, Thomas & Wachowiak, Andre
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Systematic suppression of parasitic conductivity highlights undistorted quantum transport in GaN/AlGaN 2DEGs. Journal of Crystal Growth, 589, 126673.
Schmult, S.; Wirth, S.; Silva, C.; Appelt, P.; Großer, A. & Mikolajick, T.
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Wavelength-dependent conductivity of photo-generated 2DEGs in ultra-pure GaN/AlGaN heterostructures. Journal of Crystal Growth, 594, 126788.
Chen, Hui-Tzu; Solovyev, Victor V.; Kukushkin, Igor V.; Großer, Andreas; Mikolajick, Thomas & Schmult, Stefan
