X. K. Hong

Half-metallic properties, single-spin negative differential resistance, and large single-spin Seebeck effects induced by chemical doping in zigzag-edged graphene nanoribbons.

Ab initio calculations combining density-functional theory and nonequilibrium Greens function are performed to investigate the effects of either single B atom or single N atom dopant in zigzag-edged graphene nanoribbons (ZGNRs) with the ferromagnetic state on the spin-dependent transport properties and thermospin performances. A spin-up (spin-down) localized state near the Fermi level can be induced by these dopants, resulting in a half-metallic property with 100% negative (positive) spin polarization at the Fermi level due to the destructive quantum interference effects. In addition, the highly spin-polarized electric current in the low bias-voltage regime and single-spin negative differential resistance in the high bias-voltage regime are also observed in these doped ZGNRs. Moreover, the large spin-up (spin-down) Seebeck coefficient and the very weak spin-down (spin-up) Seebeck effect of the B(N)-doped ZGNRs near the Fermi level are simultaneously achieved, indicating that the spin Seebeck effect is comparable to the corresponding charge Seebeck effect.

A high-efficiency double quantum dot heat engine

High-efficiency heat engine requires a large output power at the cost of less input heat energy as possible. Here we propose a heat engine composed of serially connected two quantum dots sandwiched between two metallic electrodes. The efficiency of the heat engine can approach the maximum allowable Carnot efficiency ηC. We also find that the strong intradot Coulomb interaction can induce additional work regions for the heat engine, whereas the interdot Coulomb interaction always suppresses the efficiency. Our results presented here indicate a way to fabricate high-efficiency quantum-dot thermoelectric devices.

Temperature-controlled giant thermal magnetoresistance behaviors in doped zigzag-edged silicene nanoribbons

Based on the nonequilibrium Greens function (NEGF) method combined with density functional theory (DFT), we investigate the spin-dependent thermoelectric transport properties of zigzag-edged silicene nanoribbons (ZSiNRs) doped by an Al–P bonded pair at different edge positions. For the ferromagnetic (FM) configuration, the strong quantum destructive interference effects between the localized states induced by the Al–P bonded pair and the side quantum states results in the appearance of spin-dependent transmission dips near the Fermi level. This fact leads to the simultaneous enhancement of the spin-filter efficiency and spin Seebeck coefficient at the Fermi level, while their signs are dependent on the doping positions. Moreover, for the antiferromagnetic (AFM) configuration, the spin-dependent transmission peaks with ordinary Lorentzian shapes near the Fermi level can be introduced by the Al–P bonded pair. Interestingly, a pure spin current in the doped AFM ZSiNRs can be achieved by modulating the temperature. In this case, the spin-filter efficiency can reach infinity, while the thermal magnetoresistance (TMR) between the FM and AFM configurations can also reach infinity.

Trap-assisted tunneling in AlGaN avalanche photodiodes

We fabricated AlGaN solar-blind avalanche photodiodes (APDs) that were based on separate absorption and multiplication (SAM) structures. It was determined experimentally that the dark current in these APDs is rapidly enhanced when the applied voltage exceeds 52 V. Theoretical analyses demonstrated that the breakdown voltage at 52 V is mainly related to the local trap-assisted tunneling effect. Because the dark current is mainly dependent on the trap states as a result of modification of the lifetimes of the electrons in the trap states, the tunneling processes can be modulated effectively by tuning the trap energy level, the trap density, and the tunnel mass.

Light absorption enhancement by embedding aluminum nanodisk arrays in rear dielectric of ultra-thin film solar cells

In this work, in order to enhance the light absorption in one micron thick crystalline silicon solar cells, a back reflecting and plasmonic nanodisk scheme is proposed. We investigate the scattering properties of aluminum nanostructures located at the back side and optimize them for enhancing absorption in the silicon layer by using finite difference time domain simulations. The results indicate that the period and diameters nanoparticles, spacer layer have a strong impact on short circuit current enhancements. This finding could lead to improved light trapping within a thin silicon solar cell device.

Rear located hemispherical silver nanoparticles for light trapping in thin film solar cells

In this work, we investigate the scattering and coupling efficiencies of the rear located hemispherical silver nanoparticles by using finite difference time domain simulations. The results indicate that the placement and diameters of silver nanoparticles have a strong impact on scattering efficiency. This finding could lead to improved light trapping within a thin silicon solar cell device.

Plasmon-enhanced light absorption of silicon solar cells using Al nanoparticles

The absorption enhancements of silicon layer in silicon solar cells with Al sphere nanoparticles are studied by the finite difference time domain (FDTD) method. The results show that the light absorption of silicon is significantly improved due to the localized surface plasmon (LSP) resonance. The relations of the absorption enhancement with the parameters of nanoparticles are thoroughly analyzed. The optimal absorption enhancement can be achieved by adjusting the relevant parameters. Specially, the silicon with the 140nm Al nanoparticles shows the most efficient absorption enhancement at optimal conditions and its maximum absorption enhancement factor is 1.4.

Study on the structure characteristics of HgCdTe infrared detector using laser beam-induced current

The structure characteristics of typical n+-on-p HgCdTe infrared detector have been studied by laser beam-induced current (LBIC). The dependence of LBIC on laser wavelength, junction depth and localized leakage has been presented. The spreading length of minority carrier of p-type region (Lsp) is extracted by the exponential decay fitting of the curve of LBIC. It is found that the peak magnitude of LBIC and junction depth approximates to a linear relationship for practical values of device fabrication. The Lsp monotonously increases with junction depth. A notable shift of LBIC profile is observed when localized leakage exists. This provides a powerful explain for LBIC applying to characterize the structure and process uniformity of HgCdTe infrared detector.