The coupling of electrothermal and optical models in multidimensional semiconductor laser simulation is a non-trivial task: While electrothermal models are conveniently formulated in a system of partial differential equations, the optical problem necessitates the solution of Maxwell's equations with results in eigenvalue problems with the eigenvalues representing lasing wavelengths and losses of the laser's modes. The state-of-the-art approach to achieve a self-consistent electro-optothermal solution os a Gummel-type iteration where the electrothermal equations (using a Newton scheme), and the optical eigenvalue problems are solved iteratively until a convergence criterion is reached. This is extremely time-consuming and unstable, especially for simulation of devices featuring closely spaced multiple modes (for example broad area lasers, VCSELs). In this work, we present a novel numerical electro-optothermal coupling scheme for semiconductor lasers which is based on the integration of the optical eigenvalue into a single global Newton formulation, The necessary derivatives are obtained by perturbation theory. The proposed scheme is more robust and decreases the computational burden (simulation time) by more than an order of magnitude compared to Gummel-type interations. This novel coupling scheme allows to investigate the influence of the electro-optothermal coupling on the device characteristics and internal physics. The effects of bias conditions on the modal dynamics, optical wavelengths, losses, and far-field patterns are analyzed. For a VCSEL, we quantify the role of gain guiding and thermal lensing.
A stable far-field and single-mode performance is of great interest for many applications in sensing or communications.
In this contribution an analysis of the far-field stability versus current and temperature is performed
for a long-wavelength vertical-cavity surface-emitting laser (VCSEL) emitting around 1310 nm. Furthermore,
the single-mode stability is investigated by means of a technology computer aided design (TCAD) tool.
The electro-opto-thermal multi-dimensional simulations are fully-coupled and use microscopic models. The optical
modes are obtained by solving the vectorial Helmholtz equation, using a finite element approach. The
impact of temperature, free carrier absorption and gain on the refractive index is accounted for. The far-field is
calculated using Green's functions.
The investigated VCSEL features an InP-based cavity with multiple quantum wells and a tunnel junction as well
as wafer-fused AlGaAs/GaAs distributed Bragg reflectors.
The comparison of simulated and measured L-I, V-I characteristics and far-field as well as the wavelength-shift
show good agreement for different ambient temperatures as well as driving current values. The simulations reveal
the impact of temperature, gain and carrier effects on the far-field. The design of optical guiding structures
(such as oxides or tunnel junctions) and its impact on the far-field behaviour over ambient temperature and bias
current is discussed.
Electrostatic Discharge (ESD) events can cause irreversible damage during production, packaging and application
of Vertical-Cavity Surface Emitting Lasers (VCSELs). Experimental investigation of those damage patterns
inside a real device is a complex and expensive task. Simulation tools can provide insight into the physics during
an actual discharge event. This paper aims to analyze ESD events in VCSELs with a microscopic simulation.
With the help of a state-of-the art Technology Computer Aided Design (TCAD) virtual ESD tests are
performed on oxide-confined VCSELs. The 2-D simulation model takes into account high-field effects and
self-heating in a hydrodynamic framework that allows time-dependent spatially resolved monitoring of critical
quantities (such as electric field across the oxide, temperature profile, current densities) during the ESD events.
Human Body Model (HBM), Machine Model (MM) and Charged Device Model (CDM) show typical local
heating and current crowding effects which may lead to irreversible damaging of the device. For slow ESD events
the temperature peak is found near the center of the device. Faster pulses show maximum temperature at the
interface between oxide and aperture. Physics-based explanations in terms of local electric field, heat generation
and heat transport are given. Oxide aperture, thickness and its position relative to the intrinsic region strongly
influence self-heating, electric fields, current density profiles and the dielectric breakdown conditions. The impact
of those factors on ESD robustness are analyzed and guidelines for robust ESD design in VCSELs are presented.
We present the static and dynamic simulation of a long-wavelength
vertical-cavity surface-emitting laser (VCSEL) operating at around
1310 nm. The device consists of AlGaAs/GaAs distributed Bragg reflectors (DBRs) which are wafer-fused to both sides of the InP-based cavity with InAlGaAs quantum wells. A tunnel junction is used for current injection into the active region. The structure is simulated with a modified version of the commercial device simulator Synopsys Sentaurus Device. The fully-coupled two-dimensional electro-opto-thermal simulations use a microscopic physics-based model. Carrier transport is described by the continuity and Poisson equations and self-heating effects are accounted for by a thermodynamic equation. To obtain the opticalmodes, the wave equation is solved using a finite element approach. The optical gain model includes many-body effects. The equations are solved self-consistently. Calibrations of static (L-I, V-I curves) and dynamic characteristics (RIN) show good agreement with measurements at different temperatures. On this basis, the simulations reveal the critical factors that determine the modulation-current efficiency factor (MCEF) of the device.
Yield enhancement and reliability improvement are main requirements in todays industrial VCSEL manufacturing. This requires a thorough understanding of process tolerances and the effects resulting
from design variations. So far, this has been done by statistical
analysis of experimental data. In this work, we use a state-of-the art technology computer aided design (TCAD) tool to analyze device
reliability and yield for multiple VCSEL designs. The starting point is a physics-based simulation model that is calibrated to temperature-dependent static and dynamic measurements for a set of single- and multi-mode VCSELs lasing at 850 nm. Applying statistical variations that result from design modifications and process fluctuations, yield and reliability data are extracted by means of simulation. The yield will be derived by compliance to selected device specifications (such available single-mode power), and the device reliability is determined from an analysis of the internal device properties. As example, the oxide aperture and metal aperture design will be discussed, and a robust design will be presented.
A novel spatially distributed noise model is used in a device simulator in order to describe relative intensity noise and frequency noise for semiconductor lasers. For charge carrier transport, continuity and Poisson equations are used and self-heating is considered by a thermodynamic equation. Spontaneous and stimulated recombination are calculated in the framework of the semiconductor Bloch equations using the second Born approximation to include many-body effects. The optical field is expanded into modes. The temporal behavior is described by a photon rate and a photon phase equation for each mode. Noise is taken into account by spatially distributed Langevin forces. The correlation functions are described directly in the frequency domain assuming small signal noise sources. All relevant equations are solved in a fully self-consistent fashion. Comparison of static characteristics and dynamic characteristics, such as relative intensity noise, with measurements show excellent agreement for a vertical-cavity surface-emitting laser (VCSEL).
We report on the simulation of 1.32μm vertical-cavity surface-emitting lasers (VCSELs). The device comprises a tunnel junction for current and optical confinement and features intra-cavity ring contacts. Distributed Bragg reflectors (DBRs) in the GaAs/AlGaAs material system form the optical cavity and are wafer-bonded to InP-based spacers. The active region consists of five InAlGaAs quantum wells (QW). For the simulations, a thermodynamic transport model is used for electrical and thermal calculations while the optical modes are computed by solving the vectorial Helmholtz equation with an finite element (FE) solver. Calibrations show good agreement with measurements and on this basis, electrical benefits of the TJ are studied. Moreover, the physics of thermal rollover are analyzed.