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Temperature-dependent cathodoluminescence spectra were measured for rock salt-structured MgxZn1−xO films with x = 0.95–0.61. The Mg0.95Zn0.05O film exhibited the shortest deep UV peak wavelength of 199 nm (6.24 eV) at 6 K. Relatively high equivalent internal quantum efficiencies of 0.9%–11% were obtained. The Tauc plots, which were obtained from temperature-dependent optical transmittance measurements, exhibited large Stokes-like shifts of 0.7–0.9 eV at 6–300 K. Time-resolved photoluminescence (PL) signals at 7 K exhibited fast and slow decay components. The fast decay component had PL lifetimes of 2.59–3.08 ns, and the slow decay component far exceeded the measurement time range of 12.5 ns. The fast decay constant reflected the transfer lifetime of the photoexcited carriers to certain trapping centers. These centers were tentatively ascribed to Zn-related isoelectronic trapped-hole centers and may be a cause of the large Stokes-like shifts. The signals at 300 K exhibited very short PL lifetimes of 120–180 ps. The PL lifetimes were mainly attributed to the nonradiative recombination lifetime. Simultaneous decreases in the Zn-related isoelectronic trapped-hole centers and the nonradiative recombination centers were found to be necessary to improve the DUV emission properties of RS-MgxZn1−xO films. [ABSTRACT FROM AUTHOR]

We investigated bandgap engineering of spinel-structured Mg B 2O4 (B = Al, Ga, In) alloys. The trend of bandgap change was tunable from approximated 7.8–3.6 eV by substituting group III cation atoms in Mg B 2O4. To evaluate the doping possibility, we have calculated the natural band alignment and doping pinning energy of the normal and inverse spinel structures of Mg B 2O4 alloys. The calculated doping pinning energies show that spinel-structured Mg B 2O4 alloys can potentially control the electron concentration, but hole doping is difficult. Our computational results are expected to provide new insights into the doping control of ultra-wide bandgap semiconductors. [ABSTRACT FROM AUTHOR]

We have calculated formation enthalpies, bandgaps, and natural band alignment for MgO1−xSx alloys by first-principles calculation based on density functional theory. The calculated formation enthalpies show that the MgO1−xSx alloys exhibit a large miscibility gap, and a metastable region was found to occur when the S content was below 18% or over 87%. The effect of S incorporation for bandgaps of MgO1−xSx alloys shows a large bowing parameter (b ≃ 13 eV) induced. The dependence of the band lineup of MgO1−xSx alloys on the S content by using two different methods and the change in the energy position of the valence band maximum (VBM) were larger than those of the conduction band minimum. Based on the calculated VBM positions, we predicted that MgO1−xSx with S content of 10%–18% can be surface charge transfer doped by high electron affinity materials. This work provides an example to design for p-type oxysulfide materials. [ABSTRACT FROM AUTHOR]

The kilogram based on the Plank constant will be realized at the National Metrology Institute of Japan (NMIJ) by using the X-ray crystal density method. In this study, for the realization, the volume of a 28Si-enriched sphere, named AVO28-S5c, was measured. The volume was determined from diameter measurements taken in many directions using an optical interferometer. The apparent volume of the sphere, which does not consider the influence of the surface layers on the volume measurement, was determined with a relative standard uncertainty of $1.8\times 10^{-8}$. The reproducibility of the kilogram realization is important for the reliable dissemination of the kilogram at the NMIJ. Therefore, the volume determined in this study was compared with that determined in 2016. These volumes were shown to agree with the uncertainty. This article provides details on the measurements, improvements of the interferometer, data analysis, and uncertainty evaluation. [ABSTRACT FROM AUTHOR]

We used first-principles calculations based on density functional theory and the Boltzmann transport equation with an empirical relaxation time scheme to investigate the thermoelectric (TE) properties of Bi2(SexTe1-x)3 alloys. We examined various TE indicators and found that Bi2SeTe2 shows relatively highest TE performance in Bi2(SexTe1-x)3 alloys than bulk Bi2Te3. The result indicated that it is difficult to find the favorable Se composition for Bi2(SexTe1-x)3 via power factor. The findings suggested that our computational framework provides a useful guide for the effect of Se incorporation on TE performance of Bi2(SexTe1-x)3 alloys. [ABSTRACT FROM AUTHOR]

Recently, α-Ga2O3 has been attracting great attentions as a new wide bandgap semiconductor, however, the reason why metastable α-Ga2O3 is grown by mist chemical vapor deposition (CVD) has not been understood. In this study, in order to elucidate growth mechanism of mist CVD-grown α-Ga2O3, growth processes in the initial stage were investigated by atomic force microscopy, transmission electron microscopy, and X-ray diffraction reciprocal space mapping. We found that the characteristics of mist CVD make the relaxation mechanisms of α-Ga2O3 on (0001) sapphire different from those of molecular beam epitaxy, pulsed-laser deposition, and metalorganic chemical vapor deposition. We also proposed the growth procedure in the initial stage. [ABSTRACT FROM AUTHOR]

The electrical and thermal transport properties of the isovalent Cu- or Sn-doped ternary phosphide Ag6Ge10P12 have been investigated. Polycrystalline ingots of Cu- and Sn-doped Ag6Ge10P12 were grown by the melting method. In Ag6−xCuxGe10P12 (x ≤ 0.3) and Ag6Ge10−ySnyP12 (y ≤ 0.25), the lattice thermal conductivity accounted for ∼95% of the total thermal conductivity. The lattice thermal conductivity of Cu- and Sn-doped Ag6Ge10P12 decreased with increasing doping concentration. Because of the decrease of the lattice thermal conductivity, the figure of merit ZT value of Ag5.85Cu0.15Ge10P12 reached ∼0.26, which was ∼60% higher than that of non-doped Ag6Ge10P12. Although the lattice thermal conductivity of Sn-doped Ag6Ge10P12 decreased, the electrical resistivity of Sn-doped Ag6Ge10P12 increased, resulting in the ZT value of Sn-doped Ag6Ge10P12 monotonically decreasing. Therefore, Cu doping of Ag6Ge10P12 is the effective way to enhance the thermoelectric performance. [ABSTRACT FROM AUTHOR]