ABSTRACT
The present research scrutinizes the influences of trade diversification, air transportation, technological innovation, and economic complexity on ecological footprint from 1990 to 2019. The findings of the both time series unit root (with and without structural break) tests confirm that none of a single variable is stationary more than the first difference. Furthermore, the Wald and nonlinear autoregressive distributed lag bound methods check asymmetry and long-term cointegration relationship between the intended variables, respectively. Moreover, this study uses the nonlinear autoregressive distributed lag model to estimate the short-run and long-run coefficients/elasticity of the ecological footprint function. Following the empirical evidence, the findings revealed that positive (negative) components in trade diversification curtail the ecological footprint in the long-run. In addition, a positive shock in air transportation leads to an increase in ecological footprint in the long-run. Nevertheless, a negative shock in air transportation exerts a significant and adverse influence on the level of ecological footprint in the long-run. Furthermore, a positive (negative) shock in technological developments significantly reduces environmental pollution in the US economy in the long-run. Besides, the outcomes from economic complexity discovered a positive shock will significantly overcome the pressure on the environment in the long-run. However, in the short-run, it is observed that negative shock in trade diversification will lead to increase the ecological footprint level in USA. Similarly, a positive shock in air transportation will lead to increase the pollution level in the short-run. In contrast, a negative shock in air transportation will lead to reduce the pressure on the environment in the short-run. Besides, in terms of policy realization, the present research recommends adopting trade synchronization, harmonic trade strategies, and investment in technological innovations to diminish the existing level of ecological footprint in the region. For sustainable development, this study put forward for instantaneously encouraging the expansion of the digital economy and reducing air pollution, accelerating the green transformation, and impelling the industrial agglomeration process in the USA.
Subject(s)
Economic Development , Inventions , Carbon Dioxide , Investments , PolicyABSTRACT
Monoclinic gallium oxide (ß-Ga2O3) is attracting intense focus as a material for power electronics, thanks to its ultra-wide bandgap (4.5-4.8 eV) and ability to be easily doped n-type. Because the holes self-trap, the band-edge luminescence is weak; hence, ß-Ga2O3 has not been regarded as a promising material for light emission. In this work, optical and structural imaging methods revealed the presence of localized surface defects that emit in the near-UV (3.27 eV, 380 nm) when excited by sub-bandgap light. The PL emission of these centers is extremely bright-50 times brighter than that of single-crystal ZnO, a direct-gap semiconductor that has been touted as an active material for UV devices.
ABSTRACT
Advancement of optoelectronic and high-power devices is tied to the development of wide band gap materials with excellent transport properties. However, bipolar doping (n-type and p-type doping) and realizing high carrier density while maintaining good mobility have been big challenges in wide band gap materials. Here P-type and n-type conductivity was introduced in ß-Ga2O3, an ultra-wide band gap oxide, by controlling hydrogen incorporation in the lattice without further doping. Hydrogen induced a 9-order of magnitude increase of n-type conductivity with donor ionization energy of 20 meV and resistivity of 10-4 Ω.cm. The conductivity was switched to p-type with acceptor ionization energy of 42 meV by altering hydrogen incorporation in the lattice. Density functional theory calculations were used to examine hydrogen location in the Ga2O3 lattice and identified a new donor type as the source of this remarkable n-type conductivity. Positron annihilation spectroscopy measurements confirm this finding and the interpretation of the experimental results. This work illustrates a new approach that allows a tunable and reversible way of modifying the conductivity of semiconductors and it is expected to have profound implications on semiconductor field. At the same time, it demonstrates for the first time p-type and remarkable n-type conductivity in Ga2O3 which should usher in the development of Ga2O3 devices and advance optoelectronics and high-power devices.
