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Harold

The Hetero-structure Laser Diode Model

Introduction Features Applications
Harold

Cross Section Simulations (Harold XY)

For the lateral structure of laser devices

Intoduction

Harold’s simulation algorithm can be extended from 1D epitaxy stack simulations to model a lateral structure such as a ridge waveguide cross section for edge emitting lasers - we refer to this as Harold XY and it is available within the base functionality of Harold.

Harold’s XY supports insulating layers, graded etching, and allows n and p-contacts to both be on the top of the structure. Its non-uniform simulation grid allows rigorous and efficient simulation of lateral current and heat spreading in the region below and either side of the active region/optical mode, which may extend for 100s of microns. In addition, it can simulate multimode operation and can simulate the change in the optical mode properties with increasing bias (hot-cavity effects). All this makes it ideal for the detailed modelling of a variety of laser designs, from simple ridge waveguide lasers to SOI hybrid lasers, high-power lasers with asymmetric waveguides and p-n blocking buried het lasers.

Harold XY simulations make use of Harold's existing layers editor, trap definition editor and mesh policy editor, making it easy to adapt and use existing 1D projects to set up XY simulations. XY simulations also have the same execution modes as a Harold's 1D simulations: Test mode (for quick diagnostics), Isothermal (pulsed), and Self-Heating (CW) modes.

Cross-section editor

The cross-section editor allows you to fully define a laser’s 2D cross-section. A cross-section is composed of a number of vertical slices, of varying widths, each of which uses its own (or a shared) epitaxial layer structure. Slices can be etched to varying depths and can also have graded etching. Each slice can have its top or bottom connected to the bias contact, the ground contact, or no contact at all.

The cross-section editor incorporates our powerful FDM Mode Solver which allows for detailed mode analysis including our Farfield Calculator. 

XY Cross-section Editor: A ridge waveguide structure with graded etching: in this case, all slices share a common layer structure; the bias contact is attached to top of ridge, ground contact extends across the bottom of all slices
XY Cross-section Editor: A ridge waveguide structure with graded etching: in this case, all slices share a common layer structure; the bias contact is attached to top of ridge, ground contact extends across the bottom of all slices

Simulations results

In addition to Per Bias results (i.e. vs. bias current/voltage/current density), Harold XY produces 2D lateral-vertical profiles of various quantities, including:

  • Electrostatic potential and electric field (vector plot)
  • Electron and hole Fermi energies
  • Conduction and valence band edges
  • Electron and hole densities (in bulk and QWs)
  • Electron and hole current densities (vector field plots)
  • Recombination rates: SRH, Auger, spontaneous emission, stimulated
  • Temperature profile
  • Optical mode
Optical mode of graded etch ridge waveguide as computed by Harold XY’s FDM Solver
Optical mode of graded etch ridge waveguide as computed by Harold XY’s FDM Solver
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Temperature profile in region around ridge waveguide, illustrating how Harold XY can efficiently model a large spatial region around the waveguide so as to obtain a realistic temperature profile. The temperature peaks in the 4-um wide ridge waveguide on the top of the structure where current is injected and most of the heating takes place. Heat then flows out into the substrate and side regions until reaching the ambient/heatsink temperature.

XY current density vector plot for ridge waveguide laser – illustrating the current spreading that occurs as the current flows out of the ridge and down to the active region
XY current density vector plot for ridge waveguide laser – illustrating the current spreading that occurs as the current flows out of the ridge and down to the active region
Profile of Auger recombination in QW of ridge waveguide laser – showing reduced Auger rate in centre of waveguide where mode intensity, and therefore stimulated recombination, is large
Profile of Auger recombination in QW of ridge waveguide laser – showing reduced Auger rate in centre of waveguide where mode intensity, and therefore stimulated recombination, is large
Laser LI curve results from a 2-mode, self-heating simulation exhibiting thermal-rollover. Curves show the total output power (blue) and the individual output powers of fundamental (green) and first order (red) waveguide modes.
Laser LI curve results from a 2-mode, self-heating simulation exhibiting thermal-rollover. Curves show the total output power (blue) and the individual output powers of fundamental (green) and first order (red) waveguide modes.
Laser LI curve results from a 2-mode, self-heating simulation exhibiting thermal-rollover. Curves show the total output power (blue) and the individual output powers of fundamental (green) and first order (red) waveguide modes.
Laser LI curve results from a 2-mode, self-heating simulation exhibiting thermal-rollover. Curves show the total output power (blue) and the individual output powers of fundamental (green) and first order (red) waveguide modes.

Comparison with PICWave, Harold and Harold QCSE

Please see here for a comparison of the active component (laser diode, SOA, modulators etc.) modelling capabilities of PICWave, Harold, Harold XY and Harold QCSE.