Akihira Munakata

SrTiO3 (STO) has attracted considerable interest as a wide-bandgap semiconductor for advanced high-k capacitors and photocatalytic applications. Although previous angle-resolved photoemission spectroscopy (ARPES) studies have characterized the valence band structure originating from O 2p orbitals, the conduction band arising from Ti 3d orbitals upon electron doping, which is called electron pockets, remains poorly understood. In this study, polarization-dependent ARPES measurements were performed on Nb 1%-doped SrTiO3 (001), enabling the direct, orbital-selective visualization of the electron pockets. From the measured band dispersion, we quantitatively determined their effective masses, anisotropy, and electron density. Our results revealed the formation of an electron pocket at the Γ point induced by Nb doping, yielding a direct bandgap energy of 3.79 eV, consistent with previous optical measurements. Furthermore, the effective masses of m1 = 0.63m0 (short-axis direction) and m2 = 8.0m0 (long-axis direction) were identified, where m0 is the free electron mass, and the Fermi surface has been shown to be ellipsoidal. The electron density derived from these dispersions was found to be 3.58 × 1020 cm−3. These findings provide a comprehensive picture of the conduction-band electronic structure that will be crucial in the design of STO-based functional devices.

Temperature dependence of barrier height in Ni/β-Ga2O3 Schottky barrier diode has been investigated in 303–573 K. The barrier height obtained by the capacitance-voltage (C-V) measurements slightly decreased with increasing temperature with the temperature coefficient of −0.51 meV/K. Since the electron mobility in β-Ga2O3 is not high, the thermionic emission-diffusion (TED) model was used for the analysis of the current-voltage (I-V) measurements. The consistent temperature coefficient of −0.49±0.02 meV/K were obtained from the C-V and I-V measurements, suggesting that the origin of the temperature dependence of the barrier height of Ni/β-Ga2O3 stems from lowering of the conduction band minimum.