Pure spin current is of central importance in spintronics. Here, we propose a two-dimensional (2D) spin-battery system that delivers pure spin current without an accompanying charge current to the outside world at zero bias. The principle of the spin battery is rooted in the photogalvanic effect (PGE) and the system has good operational stability against structural perturbation, photon energy, and other material characteristics. The principle of the device is numerically implemented in the 2D material phosphorene as an example, and first-principles calculations give excellent qualitative agreement with the physics of the PGE. The 2D spin battery is interesting as it is both a device that generates pure spin currents and also an energy source that harvests photons. Given the versatile operational space, the spin battery should be experimentally feasible.

Photodetectors based on two-dimensional materials have shown impressive performance including fast and broadband photoresponse and high responsivity.

High-$\kappa$ metal oxides are a class of materials playing an increasingly important role in modern device physics and technology. Here we report theoretical investigations of the properties of structural and lattice dielectric constants of bulk amorphous metal oxides by a combined approach of classical molecular dynamics (MD), for structure evolution, and quantum mechanical first-principles density function theory (DFT), for electronic structure analysis. Using classical MD based on the Born-Mayer-Buckingham potential function within a melt and quench scheme, amorphous structures of high-$\kappa$ metal oxides Hf${}_{1-x}$Zr${}_x$O${}_2$ with different values of the concentration $x$ are generated. The coordination numbers and the radial distribution functions of the structures are in good agreement with the corresponding experimental data. We then calculate the lattice dielectric constants of the materials from quantum mechanical first principles, and the values averaged over an ensemble of samples agree well with the available experimental data and are very close to the dielectric constants of their cubic form.

For analyzing quantum transport in semiconductor devices, accurate electronic structures are critical for quantitative predictions. Here we report theoretical analysis of electronic structures of all III-V zinc-blende semiconductor compounds. Our calculations are from density functional theory with the semilocal exchange proposed recently [Tran and Blaha, Phys. Rev. Lett. 102, 226401 (2009)], within the linear muffin tin orbital scheme. The calculated band gaps and effective masses are compared to experimental data and good quantitative agreement is obtained. Using the theoretical scheme presented here, quantum transport in nanostructures of III-V compounds can be confidently predicted.

Nonequilibrium spin injection and spin-polarized quantum transport in monolayer black phosphorus are studied using the first principles method.

We report the calculated fundamental band gaps ofwurtziteternary alloys Zn_1−xM_xO (M = Mg, Cd) and the band offsets of the ZnO/Zn_1−xM_xO heterojunctions, these II-VI materials are important for electronics and optoelectronics. Our calculation is based on density functional theory within the linear muffin-tin orbital (LMTO) approach where the modified Becke-Johnson (MBJ) semi-local exchange is used to accurately produce the band gaps, and the coherent potential approximation (CPA) is applied to deal with configurational average for the ternary alloys. The combined LMTO-MBJ-CPA approach allows one to simultaneously determine both the conduction band and valence band offsets of the heterojunctions. The calculated band gap data of the ZnO alloys scale asE_g = 3.35 + 2.33xandE_g = 3.36 − 2.33x + 1.77x²for Zn_1−xMg_xO and Zn_1−xCd_xO, respectively, wherexbeing the impurity concentration. These scaling as well as the composition dependent band offsets are quantitatively compared to the available experimental data. The capability of predicting the band parameters and band alignments of ZnO and its ternary alloys with the LMTO-CPA-MBJ approach indicate the promising application of this method in the design of emerging electronics and optoelectronics.