Growth and properties of bulk single crystals of selected transparent semiconducting oxides (TSOs): β-Ga2O3, In2O3 and SnO2

Zbigniew Galazka ,  Reinhard Uecker ,  Klaus Irmscher ,  Detlef Klimm ,  Mike Pietsch ,  Martin Albrecht ,  Detlev Schulz ,  Steffen Ganschow ,  Albert Kwasniewski ,  Robert Schewski ,  Rainer Bertram ,  Matthias Bickermann ,  Roberto Fornari 

Leibniz Institute for Crystal Growth (IKZ), Max-Born-Str 2, Berlin 12489, Germany

Abstract

β-Ga2O3, In2O3, and SnO2 are attractive transparent semiconducting oxides (TSOs) with wide bandgaps of 4.8, 2.8, and 3.6 eV, respectively. They are however, chemically unstable at elevated temperatures and tend to decompose, therefore growing such single crystals from the melt is a very challenging task. Bulk β-Ga2O3 (MP=1820°C) single crystals were grown by the Czochralski method using a self-adjusting dynamic growth atmosphere. The crystal appearance and electrical / optical properties are strongly dependent on applied growth conditions. In2O3 (MP=1950°C) is much more unstable than Ga2O3 and ZnO, and for the purpose of growing bulk In2O3 single crystals from the melt we have developed a novel crystal growth method (PCT patent application, 2012), which will be disclosed for the first time at this conference. SnO2 is the most chemically unstable compound at high temperatures (MP>2100°C) among other TSOs so that single crystals of SnO2 cannot be grown from the melt. Therefore, bulk SnO2 single crystals were obtained by the physical vapor transport (PVT). All these bulk TSO single crystals showed n-type conductivity with free electron concentrations in the range of 5x1016–5x1018 cm–3 and electron mobilities between 120–220 cm2/(V s). A systematic annealing study of the bulk TSOs at different atmospheres, temperatures, and times revealed that all the crystals are thermo-chemically stable up to 1200°C in non-reducing and up to 600–700°C in highly reducing conditions. Moreover, in terms of electrical properties, bulk TSO single crystals are sensitive to annealing conditions: the free electron concentration of bulk In2O3 crystals could be modified by more than 2 orders of magnitude, while bulk β-Ga2O3 and SnO2 crystals could be even switched interchangeably between semiconductor and electrical insulator just by suitable annealing. Availability of truly bulk TSO single crystals combined with their unique electrical and optical properties opens the door to new applications, such as high power electronics, transparent electronics, and light detectors.

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Presentation: Invited oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 2, by Zbigniew Galazka
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-04-12 15:10
Revised:   2013-04-29 11:15
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