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"Semiconducting Metal-Oxides: Recent Advances and Perspectives"

Relatore: Roberto Fornari- Dipartimento di Fisica e Scienza della Terra - Università di Parma

Aula A - Plesso di Geologia
31 Ottobre 2013 ore 16.30

Semiconducting oxides, in particular such as ZnO, Ga2O3 and In2O3, have peculiar characteristics which attracted the attention of the crystal growth and physical communities in the past few years. So far most of the research on these materials was carried out on thin layers deposited on hetero-substrates. The quality of the resulting oxide epilayers was therefore quite bad, which in turn limited the applicability of these materials. Indeed they were so far exploited as transparent conductive electrodes for solar cells or optical displays. In 2012 the first report on high-performance FETs fabricated with β-Ga2O3 single crystals triggered a lot of new efforts in order to grow high-quality bulk β-Ga2O3 and manufacture the corresponding substrates. In addition to enabling the formation of better Schottky barriers, the availability of such substrates may also allow the homoepitaxy of high-quality epilayers with lower residual carrier density and fewer extended defects, which paves the way for a new set of electronic devices, exactly as it happened with arsenides, phoshides and later with nitrides. In this presentation the melt growth of Ga2O3 and In2O3 single crystals will be reviewed. Transparent semiconducting β-Ga2O3 single crystals can be grown by the Czochralski method along the b-axis, using an iridium crucible and a suitable atmosphere in order to minimize the dissociation of Ga2O3 melt and ingot.
 In the case of In2O3 the dissociation pressure is extremely high and the Czochralski technique is not applicable. However, very recently a novel semi-closed melt growth method was developed which indeed supplied large single crystals. An important feature of both materials is given by their strong sensitivity to thermal processing. The free carrier concentration and the absorption spectra drastically vary as a function of annealing temperature, duration and ambient. [1] M. Higashiwaki, K. Sasaki, A. Kuramata,T. Masui, S. Yamakoshi, “Gallium oxide (Ga2O3) metal-semiconductor field-effect transistors on single-crystal β-Ga2O3 (010) substrates” Appl. Phys. Lett. 100, 013504 (2012) [2] Z. Galazka, R. Uecker, K. Irmscher, M. Albrecht, D. Klimm, M. Pietsch, M. Bruetzam, R. Bertram, S. Ganschow, and R. Fornari “Czochralski growth and characterization of beta-Ga2O3 single crystals”, Cryst. Res. Technol. 45, 1229 (2010). [3] Z. Galazka, R. Uecker, K. Irmscher, D. Schulz, D. Klimm, M. Albrecht, M. Pietsch, S. Ganschow, A. Kwasniewski, and R. Fornari “Melt growth, characterization and properties of bulk In2O3 single crystals”, J.Crystal Growth 362, 349 (2013).