Integrating 2D electron gas oxide heterostructures on silicon using rare-earth titanates

ABSTRACTIntegrating oxide heterostructures on silicon has the potential to leverage the multifunctionalities of oxide systems into semiconductor device technology. We present the growth and characterization of two-dimensional electron gas (2DEG) oxide systems LaTiO3/SrTiO3 (LTO/STO) and GdTiO3/SrTiO3 (GTO/STO) on Si(001). We show interface-based conductivity in the oxide films and measure high electron densities ranging from ∼9 × 1013 cm-2 interface-1 in GTO/STO/Si to ∼9 × 1014 cm-2 interface-1 in LTO/STO/Si. We attribute the higher measured carrier density in the LTO/STO films to a higher concentration of interface-bound oxygen vacancies arising from a lower oxygen partial pressure during growth. These vacancies donate conduction electrons and result in an increased measured carrier density. The integration of such 2DEG oxide systems with silicon provides a bridge between the diverse electronic properties of oxide systems and the established semiconductor platform and points toward new devices and functionalities.

Control of Polymorphism and Mass-Transfer in Al2O3 Scale on Alumina Forming Alloys

The transformation from metastable polymorphs to stable alpha-Al2O3 in the scale formed on a CoNiCrAlY alloy is accelerated under lower oxygen partial pressure (PO2), where both Al and Cr in the alloy are simultaneously oxidized, resulting in the formation of a dense and monolithic alpha-Al2O3 scale. Under higher PO2, where all components of the alloy are oxidized, the transformation is retarded and (Co,Ni)(Al,Cr)2O4 is also produced. The oxygen permeability in polycrystalline alpha-Al2O3 wafers exposed to steep oxygen potential gradients is evaluated at high temperatures to investigate the complicated mass-transfer phenomena through the scale formed on the alloy. The diffusion of Al and O species, which are responsible for the oxygen permeation along the grain boundaries of Al2O3, is dependent on the formation of an oxygen potential gradients. For Lu-doped Al2O3 polycrystals, it was found that Lu depressed the mobility of oxygen, but did not directly influence the migration of Al.