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The 14th International NUSOD Conference welcomes researchers from six continents who present about 100 papers, including 9 invited talks. The conference sessions cover a wide range of topics, such as novel materials and devices, nanostructures, laser diodes, photodetectors, solar cells, light-emitting diodes as well as numerical methods.
We present a theoretical method for calculations of exciton and bi-exciton energies in type-II colloidal quantum dots. Our methodology is based on an 8-band k · p Hamiltonian of the zinc-blend structure, which incorporates the effects of spin-orbit interaction, strain between the core and the shell and piezoelectric potentials. Exciton states are found using the configuration interaction (CI) method...
Different numerical simulations of quantum-dot heterostructures derived from experimental results are presented. We extrapolated three-dimensional dot models directly by atomic force microscopy and high-resolution transmission electron microscopy results, and we present electromechanical, continuum k→ · k→, atomistic Tight Binding and optical calculations for these realistic structures, also compared...
A quantum-electrodynamics model is developed for a nanolaser with a semiconductor quantum-dot gain region. Intensity, coherence time and photon autocorrelation function are calculated, especially during transition from below to above lasing threshold.
In this work, an ultracompact electro-optic modulator based on refractive index modulation by plasma dispersion effect in PhC all-optical gate (AOG) is proposed. The index modulation is achieved by applying a time-varying bias voltage across the electrical contacts of the AOG. The proposed modulator has potential for high-speed operation, with bandwidths in excess of 30GHz achievable.
Auger recombination and the relaxation of the resulting excited electrons are investigated in III-nitride light-emitting diodes (LEDs) with a full-band Monte Carlo carrier transport model to assess the possibility of recovering Auger signatures from experiments. Full-Brillouin-zone calculations of Auger coefficients indicate that Auger recombination may not be negligible for LED operation, although...
In this work we present the effect of compositional fluctuations in InGaN/GaN quantum wells (QWs) on their spontaneous emission properties. We show that random alloy fluctuations lead to fluctuations of both the optical matrix elements and the emission energy and that the two quantities are correlated. A qualitatively different behaviour between flat band QWs and QWs with strong quantum confined Stark...
We present results from a combined experimental and numerical investigation of a blue InGaN/GaN LED test structure grown on a SiC substrate, confirming that tunneling represents a critical contribution to the sub-threshold forward-bias current and discussing the relative importance of different trap-assisted electron tunneling processes.
Simulations using continuum elasticity theory and an eight-band k · p approach suggest the reduction of the diameter of InxGa1−xN/GaN axial nanowire heterostructures to be a promising approach to increase the intensity of light emitting processes. A reduction of the nanowire diameter significantly reduces the magnitude of surface potentials and thus leads to a much larger overlap of the electron and...
The paper reviews applications of ABC-model to interpret internal quantum efficiency and its droop in III-nitride light-emitting diodes (LEDs). Advantages of the model, its intrinsic limitations, and tentative mechanisms responsible for deviation of the model predictions from available observations are discussed. New experimental information on recombination processes in the LED active regions coming...
GaN-based light-emitting diodes (LEDs) exhibit a severe efficiency droop with increasing current. The physical mechanisms behind this droop phenomenon are still under dispute, but most droop models hold the rising carrier density inside the quantum wells responsible. This paper analyses a new approach to circumvent the droop problem by raising the quantum efficiency beyond 100% utilizing multiple...
We study electron dynamics in a multi-quantum well (MQW) light-emitting diode (LED) using Monte Carlo simulation and show that at strong injection, Auger recombination in the quantum wells creates a hot electron population which is still visible at the p-contact 250 nm away from the MQW. The Auger-excited electrons also generate a leakage current that is notably larger than leakage predicted by drift-diffusion,...
Light-emitting diode (LED) with designed metal electrode to the top p-semiconductor layer is studied. Original numerical model and procedure are developed for the LED with nonuniform distributions of electrical and optical characteristics caused by the mesh-like configuration of the top electrode. The proposed approach can be used to optimize the LED ouput optical performance by proper choice of the...
In this paper, we established a optical model and made an analysis of GaN-based LED flip chip by double-sided PSS (patterned sapphire substrate). The result analysis shows that the small distance and large radius of micro-cylinder and micro-hemisphere for cylindrical and hemispherical PSS would be more effective to enhance LED efficacy. The hemispherical pattern is more efficient than the cylindrical...
We present a multiband envelope-function model for wurtzite nanostructures based on a rigorous numerical procedure to determine operator ordering and band parameters from nonlocal empirical pseudopotential calculations. The proposed approach leads to numerically stable envelope equations that accurately reproduce full-Brillouin-zone subband dispersions of quantum systems obtained within the linear...
Electrical characteristics of GaAs-based blocked-impurity-band (BIB) detector are numerically studied. Electron density and electric field distributions of the device are presented with consideration of immaturity of GaAs blocking layer. Temperature-dependent dark current characteristics are then simulated by taking into account impurity-band effects.
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