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ACS Appl Mater Interfaces. 2016 Jun 1;8(21):13181-6. doi: 10.1021/acsami.6b01582. Epub 2016 May 17.

Density and Capture Cross-Section of Interface Traps in GeSnO2 and GeO2 Grown on Heteroepitaxial GeSn.

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Imec , Kapeldreef 75, Leuven B-3001, Belgium.
Department of Metallurgy and Materials Engineering (MTM), KU Leuven , Kasteelpark Arenberg 10, Leuven B-3001, Belgium.
Department of Solid State Sciences, Ghent University , Krijgslaan 281/S1, Gent B-9000, Belgium.
Department of Physics and Astronomy, KU Leuven , Celestijnenlaan 200D, B-3001 Leuven, Belgium.
Department of Electronics and Information Systems, Ghent University , Sint-Pietersnieuwstraat 41, B-9000 Gent, Belgium.


An imperative factor in adapting GeSn as the channel material in CMOS technology, is the gate-oxide stack. The performance of GeSn transistors is degraded due to the high density of traps at the oxide-semiconductor interface. Several oxide-gate stacks have been pursued, and a midgap Dit obtained using the ac conductance method, is found in literature. However, a detailed signature of oxide traps like capture cross-section, donor/acceptor behavior and profile in the bandgap, is not yet available. We investigate the transition region between stoichiometric insulators and strained GeSn epitaxially grown on virtual Ge substrates. Al2O3 is used as high-κ oxide and either Ge1-xSnxO2 or GeO2 as interfacial layer oxide. The interface trap density (Dit) profile in the lower half of the bandgap is measured using deep level transient spectroscopy, and the importance of this technique for small bandgap materials like GeSn, is explained. Our results provide evidence for two conclusions. First, an interface traps density of 1.7 × 10(13) cm(-2)eV(-1) close to the valence band edge (Ev + 0.024 eV) and a capture cross-section (σp) of 1.7 × 10(-18) cm(2) is revealed for GeSnO2. These traps are associated with donor states. Second, it is shown that interfacial layer passivation of GeSn using GeO2 reduces the Dit by 1 order of magnitude (2.6 × 10(12) cm(-2)eV(-1)), in comparison to GeSnO2. The results are cross-verified using conductance method and saturation photovoltage technique. The Dit difference is associated with the presence of oxidized (Sn(4+)) and elemental Sn in the interfacial layer oxide.


DLTS; GeSn; capture cross-section; interface traps Dit; virtual Ge substrate


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