| AVS 61st International Symposium & Exhibition | |
| Electronic Materials and Processing | Thursday Sessions |
| Session EM1-ThA |
| Session: | Materials for Quantum Computation |
| Presenter: | Martin McDaniel, The University of Texas at Austin |
| Authors: | M.D. McDaniel, The University of Texas at Austin T.Q. Ngo, The University of Texas at Austin A.B. Posadas, The University of Texas at Austin C. Hu, The University of Texas at Austin S.N. Chopra, The University of Texas at Austin E.T. Yu, The University of Texas at Austin A.A. Demkov, The University of Texas at Austin J.G. Ekerdt, The University of Texas at Austin |
| Correspondent: | Click to Email |
Crystalline strontium hafnate, SrHfO3 (SHO), is an ideal candidate to study as a suitable high-k gate dielectric on Ge. SHO (a ~ 4.069 Å) has a reasonable lattice match to the Ge (001) surface (a/√2 ~ 3.992 Å), yielding a ~1.9% compressive strain in the epitaxial film. SHO shows a high permittivity (k~20) with appropriate band alignment (~1 eV offset) to Ge. In addition, the crystalline nature of the SHO film is expected to drastically reduce the interface trap density at the oxide-Ge interface. We will report our recent results on the growth, characterization, and electrical performance, of epitaxial SHO films and heterostructures for next-generation high-k dielectrics on Ge.
In our recent publication, we reported on the direct growth of crystalline strontium titanate, SrTiO3 (STO), on Ge via atomic layer deposition.[1] Electrical measurements of a 15-nm thick undoped STO film show a large dielectric constant (k~90), but high leakage current (~10 A/cm2 at +1 eV). In the present work, the unfavorable conduction band offset (and high leakage current) of STO on Ge is circumvented by growing the Hf-based perovskite, SHO. For the growth of SHO, we employ the commercially available strontium bis(triisopropylcyclopentadienyl) and hafnium formamidinate precursors. After thermal deoxidation, the Ge substrate is transferred in vacuo to the deposition chamber where a thin film of SHO (2-4 nm) is deposited by ALD at 225 °C. Following post-deposition annealing at 700 °C, the perovskite film becomes crystalline with epitaxial registry to the underlying Ge (001) substrate. In situ x-ray photoelectron spectroscopy confirms stoichiometric to Sr-rich films with no GeOx formation or carbon impurities.
Ex situ x-ray diffraction confirms the perovskite structure and orientation of the SHO film. Thicker SHO films (above 2 nm) appear to show a relaxed lattice constant, indicating relaxation of the epitaxial film above the critical thickness. The electrical performance of several SHO films and heterostructures will be presented. In general, the leakage current is reduced by several orders of magnitude for the SHO films versus STO on Ge. The current work demonstrates the promise for crystalline oxides grown by ALD on Ge for advanced semiconductor devices, including high-mobility Ge-based transistors.
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[1] M. D. McDaniel et al., “A Chemical Route to Monolithic Integration of Crystalline Oxides on Semiconductors,” accepted to Adv. Mater. Interfaces (2014), doi: 10.1002/admi.201400081.