Dan Liang

Quasiparticle and optical properties of strained stanene and stanane

Quasiparticle band structures and optical properties of two dimensional stanene and stanane (fully hydrogenated stanene) are studied by the GW and GW plus Bethe–Salpeter equation (GW-BSE) approaches, with inclusion of the spin-orbit coupling (SOC). The SOC effect is significant for the electronic and optical properties in both stanene and stanane, compared with their group IV-enes and IV-anes counterparts. Stanene is a semiconductor with a quasiparticle band gap of 0.10 eV. Stanane has a sizable band gap of 1.63 eV and strongly binding exciton with binding energy of 0.10 eV. Under strain, the quasiparticle band gap and optical spectrum of both stanene and stanane are tunable.

Electronic and excitonic properties of two-dimensional and bulk InN crystals

Motivated by potential extensive applications in nanoelectronics devices of III-Vmaterials, we calculate the structural and optoelectronic properties of two-dimensional (2D) InN as well as its three-dimensional (3D) counterparts by using density functional theory (DFT). Compared with the 3D form, the In-N bonding in the 2D InN layer is stronger in terms of the shorter bond length, and the formation of the 2D one is higher in terms of the lower cohesive energy. The bandgap of monolayer InN is 0.31 eV at PBE level and 2.02 eV at GW(0) level. By many-body GW(0) and BSE within RPA calculations, monolayer InN presents an exciton binding energy of 0.12 eV. The fundamental bandgap increases along with layer reduction and is converted from direct (0.7-0.9 eV) in bulk InN to indirect (2.02 eV) in monolayer InN. Under biaxial compressive strain, the bandgap of 2D-InN can be further tuned from indirect to direct.

k ⋅ p calculations of bismuth induced changes in band structure of InN1−xBix, GaN1−xBix and AlN1−xBix alloys

Valence band anticrossing (VBAC) model is used to investigate band structure of InN1-xBix, GaN1-xBix and AlN1-xBix for the purpose of optimal performance group-III nitride related devices. Obvious reduction in band gap and increase in spin-orbit splitting energy are founded by doping dilute concentration of bismuth in all these III-N material. The band gap of GaN1-xBix and AlN1-xBix show a step change, and this can be explained by the special position relation between of Bi impurity energy level with corresponding hosts band offsets. We also show how bismuth may be used to form alloys by finding the doping region ΔSO > Eg which can provide a means of suppressing non-radiative CHSH (hot-hole producing) Auger recombination and inter-valence band absorption. For InN1-xBix, bismuth concentration beyond 1.25% is found to be corresponding to the range of ΔSO > Eg and it shows a continuous adjustable band gap from 0.7 eV to zero. This may make InN1-xBix a potential candidate for near or mid-infrared optoelectronic applications.

Closing the bandgap for III-V nitrides toward mid-infrared and THz applications

A theoretical study of InNBi alloy by using density functional theory is presented. The results show non-linear dependence of the lattice parameters and bulk modulus on Bi composition. The formation energy and thermodynamic stability analysis indicate that the InNBi alloy possesses a stable phase over a wide range of intermediate compositions at a normal growth temperature. The bandgap of InNBi alloy in Wurtzite (WZ) phase closes for Bi composition higher than 1.5625% while that in zinc-blende (ZB) phase decreases significantly at around 356 meV/%Bi. The Bi centered ZB InNBi alloy presents a change from a direct bandgap to an indirect bandgap up to 1.5625% Bi and then an oscillates between indirect bandgap and semi-metallic for 1.5625% to 25% Bi and finally to metallic for higher Bi compositions. For the same Bi composition, its presence in cluster or uniform distribution has a salient effect on band structures and can convert between direct and indirect bandgap or open the bandgap from the metallic gap. These interesting electronic properties enable III-nitride closing the bandgap and make this material a good candidate for future photonic device applications in the mid-infrared to THz energy regime.

First-principles study on electronic properties of stanene/WS2 monolayer

We present first-principles calculations to study the stability and electronic properties of stanene on WS2 hybrid structure. It can be seen that the stanene is bound to WS2 substrate with an interlayer distance of about 3.0 A with a binding energy of −51.8 meV per Sn atom, suggesting a weak interaction between stanene and WS2. The nearly linear band dispersion character of stanene can be preserved with a sizeable band gap in stanene on WS2 hybrid structure due to the difference of onsite energy induced by WS2 substrate, which is more helpful to the on–off current ratio in the logical devices made of stanene/WS2. Moreover, the band gaps, the position of Dirac point with respect to Fermi level, and electron effective mass (EEM) of stanene on WS2 hybrid structure can be tuned by the interlayer distance, external electric field and strains. These results indicate that stanene on WS2 hybrid structure is a promising candidate for stanene-based field-effect transistor (FET) with a finite band gap and high carrier mobility.