Suihu Dang

Electronic structure and ferromagnetic properties of Cu-doped AlN from first principles

Using the first-principles method based on the density functional theory, we studied the ferromagnetic stability and electronic structure of (Al, Cu) N. The Cu dopants were found spin polarized and the calculated band structure suggested a 100% polarization of the conduction carriers. The ferromagnetic ground state in Cu-doped AlN can be explained in terms of p‐d hybridization mechanism. Based on the analysis on Cu-doped ZnO [L. H. Ye et al., Phys. Rev. B 73, 033203 (2006)], Curie temperature (TC) higher than 350K can be expected in AlN doped with Cu. These results suggest that the Cu-doped wide band AlN may present a promising dilute magnetic semiconductor and find applications in the field of spintronics.

Performance enhancement of GaN-based light-emitting diodes by surface plasmon coupling and scattering grating

Using the analysis of the evanescent surface plasmon polariton (SPP) mode at the GaN/Ag interface as basis, we propose a light-emitting diode (LED) structure with a plasmonic Ag nanostructure and sapphire grating to enhance external quantum efficiency. The 2D finite-difference time-domain method is used to study the spectral properties of the hybrid structure and the effects of structural parameters on light emission enhancement. The plasmonic Ag nanostructure couples recombination energy to the SPP modes at the GaN/Ag interface, whereas the sapphire grating scatters photons out of the LED chips with high extraction efficiency. Under optimal parameters, external quantum efficiency enhancement increases to approximately eighteen times the original value at a relatively long wavelength.

Improvement of light extraction efficiency of GaN-based light-emitting diodes using Ag nanostructure and indium tin oxide grating.

Based on the analysis of the evanescent wave from total internal reflection, a light-emitting diode (LED) structure with a plasmonic Ag nanostructure and indium tin oxide (ITO) grating was proposed to enhance the extraction efficiency. The two-dimensional finite-difference time-domain method was used to study the spectral properties of the hybrid structure and the effects of structure parameters on extraction enhancement. The results demonstrate that the plasmonic Ag nanostructure can couple the evanescent wave to a propagation wave around the GaN/ITO interface, and then the photons are scattered out of the LED chips by the ITO grating with high extraction efficiency. Under the optimal parameters, the light extraction efficiency can reach approximately three times the original value at a relatively longer wavelength.

Theoretical studies on transforming a GaN semiconductor into a photonic crystal under a periodic external magnetic field

In this study, the properties of light propagation for a GaN semiconductor when subjected to a periodic external magnetic field were calculated by means of a transfer matrix. The dielectric function which was modulated periodically by the periodic external magnetic field caused changes of photonic band gap (PBG). In the reflection spectra, photons can be localized in the narrow bands. The position and intensity of PBGs can be modulated by changing the periodic external magnetic field and angle of the incident electromagnetic wave. All of these results have shown that a semiconductor has functions similar to conventional photonic crystals subjected to periodic external magnetic field.

Effects of polarization field distribution on photoelectric properties of InGaN light-emitting diodes

Effects of the polarization field distribution in the quantum well layer of InGaN light-emitting diodes (LEDs) on their photoelectric properties are numerically studied. Specifically, the polarization and built-in electricfield distributions, energy band diagrams, carrier concentrations, radiative recombination rate, carrier current density, electroluminescence (EL) spectra, and internal quantum efficiency (IQE) are investigated. The simulation results suggest that the triangular polarization field distribution contributes to uniform carrier distribution in the quantum wells, which inhibits electron current leakage and enhances radiative recombination. In addition, the effects of the polarization field on InGaN multiple quantum wells (MQWs) are effectively suppressed by implementation of triangular MQWs, which leads to minimization of the resulting efficiency droop. LEDs incorporated with triangular MQWs with gallium face-oriented inclination band profiles exhibit a 128% improvement in EL intensity at 20 mA and a 9% reduction in droop at 100 mA in comparison to the conventional square-MQW LEDs.

Carrier Transport Improvement in Blue InGaN Light-Emitting Diodes Via Reduced Polarization Using a Band-Engineered Electron Blocking Layer

This study numerically investigates the effect of using a new electron blocking layer (EBL) for blue InGaN light-emitting diodes (LEDs) to improve hole injection efficiency and electron confinement. Simulation results suggest that the carrier transportation behavior of the EBL can be appropriately modified by adept control of the graded AlGaN layer. Furthermore, when compared with the conventional LED structure, the redesigned LED with graded AlGaN layer shows a slight improvement in forward voltage Vf and a significant enhancement in light output power. The redesigned LED can achieve an exceptional increment of 106.6% in light output power at 100 mA when compared with conventional LED. The observed improvement in the photoelectric performance of blue LEDs is primarily due to the reduced polarization effect at the last-barrier/EBL interface, as a result of the graded Al composition in EBL.