A gas sensor based on a ZnGa₂O₄(ZGO) thin film grown by metalorganic chemical vapor deposition operated under the different temperature from 25 °C to 300 °C is investigated in this study. This sensor shows great sensing properties at 300 °C. The sensitivity of this sensor is 22.21 as exposed to 6.25 ppm of NO and its response time is 57 s. Besides that, the sensitivities are 1.18, 1.27, 1.06, and 1.00 when exposed to NO₂(500 ppb), SO₂ (125 ppm), CO (125 ppm), and CO₂ (1500 ppm), respectively. These results imply that the ZGO gas sensor not only has high sensitivity, but also has great selectivity for NO gas. Moreover, the obtained results suggest that ZGO sensors are suitable for the internet of things(IOT) applications.

Gallium nitride films, epitaxially grown on Si(111) via a lattice-matched ${\mathrm{ZrB}}_2$ buffer layer by plasma-assisted molecular beam epitaxy, have been studied in situ by noncontact atomic force microscopy and also in real time by reflection high-energy electron diffraction. The grown films were determined to be always N-polar. First-principles theoretical calculations modeling the interface structure between GaN(0001) and ${\mathrm{ZrB}}_2(0001)$ clarify the origin of the N polarity.

We conduct first-principles total-energy density functional calculations to study the heteroepitaxial growth behavior of GaN(0001) on $\mathrm{Zr}{\mathrm{B}}_2\left(0001\right)$ substrates. Using repeated free-surface terminated slabs, our calculated surface energies suggest that the $\mathrm{Zr}{\mathrm{B}}_2\left(0001\right)$ surface is Zr terminated. The relative stability of six different models of the $\mathrm{Ga}\mathrm{N}\left(0001\right)∕\mathrm{Zr}{\mathrm{B}}_2\left(0001\right)$ interface is examined as a function of the chemical potentials of Ga and Zr, and the most favorable interface consists of tetrahedrally coordinated N with one Ga-N bond and three N-Zr bonds. This interface structure gives rise to N-polarity in the GaN epitaxial film. Both of these findings agree with previously reported experimental results.

We conduct first-principles total-energy density functional calculations to study the band structures in Ge1−xSnx infrared semiconductor alloys. The norm-conserving optimized pseudopotentials of Ge and Sn have been constructed for electronic structure calculations. The composition-bandgap relationships in Ge1−xSnx lattices are evaluated by a detailed comparison of structural models and their electronic band structures. The critical Sn composition related to the transition from indirect- to direct-gap in Ge1−xSnx alloys is estimated to be as low as x∼ 0.016 determined from the parametric fit. Our results show that the crossover Sn concentration occurs at a lower critical Sn concentration than the values predicted from the absorption measurements. However, early results indicate that the reliability of the critical Sn concentration from such measurements is hard to establish, since the indirect gap absorption is much weaker than the direct gap absorption. We find that the direct band gap decreases exponentially with the Sn composition over the range 0 <x 0.375, in very good agreement with the theoretical observed behavior [D. W. Jenkins and J. D. Dow, Phys. Rev. B 36, 7994, 1987]. For homonuclear and heteronuclear complexes of Ge1−xSnx alloys, the indirect band gap at L-pointis is found to decrease homonuclear Ge-Ge bonds or increase homonuclear Sn-Sn bonds as a result of the reduced L valley. All findings agree with previously reported experimental and theoretical results. The analysis suggests that the top of valence band exhibits the localization of bond charge and the bottom of the conduction band is composed of the Ge 4s4p and/or Sn 5s5p atomic orbits.