Solid State Physics Seminar

Transparent semiconducting oxides (TSOs) constitute a class of oxide materials combiningboth semiconducting behaviour and transparency in the visible / UV spectral region arisingfrom wide or ultra-wide bandgaps. The TSOs drive extensive research towards novel devicesand applications, especially in electronics and UV opto-electronics among others. In most cases, a device development depends on the availability of bulk single crystals,mainly functioning as lattice-matched substrates for homoepitaxial growth and devicefabrication in different architectures. High melting points and thermal instability of the TSOsmake the crystal growth directly from the melt difficult and demanding, often requiring novelapproaches in crystal growth technology. All the TSO compounds to be discussed were grownat IKZ and include binary (ZnO, In2O3, SnO2, r-GeO2, β-Ga2O3), ternary (β-(AlxGa1-x)2O3,MgGa2O4, ZnGa2O4, BaSnO3, ZnSnO3), and quaternary (Zn1-xMgxGa2O4, InGaZnO4) systems. An overview will include main aspects of crystal growth and basic physical properties ofobtained crystals, with the focus on electrical properties. Two prominent compounds β-Ga2O3and β-(AlxGa1-x)2O3 will be discussed in more detail to reveal challenges in crystal growth byvarious methods, wafer preparation, and film growth by MOVPE. An emerging TSO compound,r-GeO2, will also be a subject of the more detailed presentation. The TSOs attract considerableattention worldwide, particularly for high-power electronic devices to improve voltageconversion efficiency by replacing large and heavy transformers with very small powermodules. With this respect, perspectives for ultra-wide bandgap β-Ga2O3, β-(AlxGa1-x)2O3, andr-GeO2 materials will be highlighted.