Sebastian Steiger

Electroluminescence from a Quantum-Well LED using NEGF

Nonequilibrium Greens functions (NEGF) are employed to model carrier transport and luminescence in a single-quantum-well light-emitting diode (LED). The sound theoretical formalism allows for a consistent description of coherence loss as well as fundamental scattering mechanisms and reveals details about physical phenomena such as the quantum-confined Stark and Franz-Keldysh effects, tunneling and carrier capture. A comparison to semiclassical results is made and similarities as well as differences are highlighted.

tdkp/AQUA: Unified modelling of electroluminescence in nanostructures

This article summarizes the capabilities of the optoelectronic simulation framework tdkp/AQUA aimed at the description of electroluminescence in semiconductor nanostructures such as light-emitting diodes (LEDs). tdkp is a standalone finite-element software able to accurately calculate strain, built-in fields due to spontaneous and piezoelectric polarization, quantum states, gain and luminescence spectra in zero- to three-dimensional structures. AQUA calculates transport through nanostructures using an original model which accounts for the distinct behaviour of carriers confined to active regions and unconfined carriers. Furthermore, it computes electroluminescence spectra via a self-consistent coupling of the confined carriers to quantum-mechanical calculations using tdkp. Two examples are presented which highlight the versatility and generality of the developed simulator.

Electroluminescence in Nanostructures of Different Dimensionalities: A Comparative Simulation Study

We employ our simulation framework TDKP/AQUA to investigate bulk, planar quantum-well and V-groove quantum-wire light-emitting diodes. Carrier transport and spontaneous light emission are calculated self-consistently for all degrees of quantization. The simulation is based on a semi-coherent picture of drift and diffusion along unquantized directions whereas confinement and luminescence are calculated from a multiband Schroedinger equation in the confined directions. The three structures with different quantization degrees are compared with respect to light conversion efficiency and overall output power. It is shown that carrier confinement greatly improves the radiative conversion efficiency but at the same time limits output power and enhances carrier leakage into the minority regions due to a reduced density of states.

Ellipticity and spurious solutions in k⋅p calculations of III-nitride nanostructures

We analyze the ellipticity of the standard kldrp Wurtzite model for the symmetrized and the Burt-Foreman operator ordering. We find that the symmetrized Hamiltonian is unstable, leads to different results and can cause spurious solutions. We show that the operator ordering in Wurtzite must be completely asymmetric to be stable. The asymmetric operator ordering is elliptic and therefore no spurious solutions are obtained.

Optical gain in 407nm and 470nm InGaN/GaN heterostructures: signature of quantum-dot states

In this contribution, a detailed analysis of optical gain in InGaN/GaN quantum structures with Indium content of 10% and 20% is presented. Experimental data are obtained from Hakki-Paoli characterization of edge-emitting Fabry-Perot lasers. A gain model that includes many-particle effects on a microscopic level, as well as combined quantum-well and quantum-dot density of states, is used to explain the experimental findings. Inhomogeneous broadening arising from local Indium clusters is included via a statistical fluctuation of the electronic density of states. Excellent agreement is obtained for the characteristic gain spectra from structures emitting at 405nm (10% In content) and 470nm (20% In content), and a systematic analysis of the microscopic physics shows signature of quantum-dot states.