This paper illustrates how technology computer-aided design (TCAD), which nowadays is an essential part of CMOS
technology, can be applied to LED development and manufacturing. In the first part, the essential electrical and optical
models inherent to LED modeling are reviewed. The second part of the work describes a methodology to improve the
efficiency of the simulation procedure by using the concept of process compact models (PCMs). The last part
demonstrates the capabilities of PCMs using an example of a blue InGaN LED. In particular, a parameter screening is
performed to find the most important parameters, an optimization task incorporating the robustness of the design is
carried out, and finally the impact of manufacturing tolerances on yield is investigated. It is indicated how the concept
of PCMs can contribute to an efficient design for manufacturing DFM-aware development.
We present a calibrated full-3D simulation of a widely-tunable sampled-grating distributed Bragg reflector (SGDBR) laser showing the characteristic quasi-continuous tuning map. The SGDBR laser is a longitudinally integrated device consisting of five waveguide sections: a front and rear mirror section together with a phase section allow for quasi-continuous tuning over a wavelength range of 100nm, while an active section provides the optical gain for the laser operation. For real world applications the tuning behavior needs to be well understood in order to guarantee stable operation for each wavelength channel. Due to the strong inhomogeneities both in the transverse and longitudinal dimensions a 3D simulation model is necessary to cover the full complexity of such devices. In our physics-based approach, we solve the fully coupled semiconductor drift-diffusion equations for electrons and holes, taking into account longitudinal current flux in full 3D. Gain calculation and the photon rate equation are included self-consistently in an iterative Newton scheme. The optical field is composed of several transverse mode patterns combined with the longitudinal field distribution as obtained by a transfer matrix formalism. By means of a Gummel-type iteration scheme a self-consistent solution of the optics and electronics is found. We show that this approach succeeds even in the numerically most challenging case of discrete wavelength jumps as observed in typical tuning maps of SGDBR lasers. Our simulations are in good agreement with measurements and prove the suitability of the simulator for the design and optimization of state-of-the-art tunable lasers.
We demonstrate a comprehensive multi-dimensional DBR laser simulation. The DBR laser under investigation consists of three longitudinally integrated waveguide sections: an active section providing the optical gain for the laser operation, a passive phase shift section which contains neither gratings nor active material and a DBR mirror section. This structure is representative for longitudinally integrated devices such as widely tunable sampled-grating laser diodes. In our physics-based approach, we solve the fully coupled semiconductor drift-diffusion equations for electrons and holes and the temperature diffusion equation, taking into account longitudinal current and heat flux. Gain calculation and the photon rate equation are included self-consistently. A general and comprehensive solution of the transverse optical field is combined with the longitudinal field distribution including general DBR sections. The simulator is applied for the design and optimization of state-of-the-art tunable lasers. It proofs to be an effective tool for bandgap engineering, for the optimization of the transverse confinement of the optical mode as well as the current, and for thermal management.
This work deals with the TCAD (technology computer aided design) based design of VCSEL (vertical-cavity surface emitting laser) devices. A comprehensive 2D electro-thermo-optical device model is presented. Furthermore, as examples, a micromechanical, electrostatically actuated vertical optical resonator is
investigated, a procedure for optimising the higher order mode suppression in a VCSEL is presented, and a coupled electro-thermo-optical simulation of a VCSEL is performed.
The laser device model employs the photon rate equation approach. It is based on the assumption that the shapes of the optical modes depend on the instantaneous value of the time-dependent dielectric function.
The optical fields in the VCSEL cavity are expanded into modes obtained from the complex frequency representation of the homogeneous vectorial Helmholtz equation for an arbitrary complex dielectric function. The 3D problem is transformed into a set of 2D finite element (FE) problems by using a Fourier series expansion of the optical field in azimuthal direction. For the bulk electro-thermal transport a 2D thermodynamic model is employed in a rotationally symmetric body. Heterojunctions are modeled using a thermionic emission model. Quantum wells are treated as scattering centres for
carriers. The optical gain and absorption model in the quantum well active region is based on Fermi's Golden Rule. The sub-bands in the quantum well are determined by solving the stationary effective mass Schroedinger equation with parabolic band approximation for the electrons, light and heavy holes.