Disk MQW Laser

laserex09.in : Disk MQW Laser

Requires: Blaze/Quantum/Laser
Minimum Versions: Atlas 5.28.1.R

This example demonstrates the simulation of a tunnel injection InGaAsP/InAsP disk laser. The Disk laser has a cylindrical cavity, which favors lasing of modes with high azimuthal (orbital) number. The fact that this is a tunnel injection laser has an important modeling implication. Since hot carriers are suppressed in the active region due to tunnel injection directly to low energy bound states, the carrier density in active region is predominantly fully 2 dimensional. Thus as opposed to a conventional laser, the capture-escape model is not necessary to dynamically couple the bound state density to bulk carriers in the active region.

To model the optical response in the active region, the deck employs the Luttinger-Kohn model k.p band structure model using the KP.CV2 parameter on the MODELS statement. The quantum wells are treated as coupled. The optical gain and spontaneous emission are computed using integration over k-space. The integration can be activated by the KP.ADAPTIVE parameter on MODELS statement. It is not activated by default in this example to reduce simulation time.

The deck employs a 2D cylindrical vector Helmholtz solver to find intensity and optical field distribution in R-Z plane of the cavity. The orbital number is set by ORBIT parameter on the LASER statement. If a range of orbital numbers is desired, set parameters ORB.MIN and ORB.MAX. Metal electrodes are excluded from the solution domain by swtching off HELMHOLTZ parameter on the REGION statement. Perfect Electric Conductor boundary conditions are used at the boundaries of the domain.

Details of extraction of light from the cavity is not modeled here. Instead, exctraction losses are set by parameter EXTR.LOSS [1/cm], which is included in the photon rate equations. Mirror losses are kept at zero by setting mirror reflectivities to 100% . Parameter PHOTON.ENERGY is the initial guess for the cavity eigen mode's energy. The actual eigen energies are printed on the screen, when parameter PRT.EVAL is specified on the LASER statement.

The deck uses voltage boundary conditions throughout the simulation. The voltage boundary conditions were found to provide better stability and performance in the simulation.

The important modeling highlights are:

  • k.p bandstructure based calculation of gain and spontaneous emission in the active region. The band structure is computed with strain effects and full coupling to the electrostatic potential at every bias step.
  • Multi-transverse mode simulation of disk laser, with mode competition
  • Demonstration of a 2D vector Helmholtz solver for disk geometry with full coupling to the changes in the complex refractive index due to the gain computed from the k.p model, and free-carrier absorption from the bulk carrier density in the device.
  • Tunnel injection modeled using a non-local tunneling junction.

The results show the total power emitted, modal photon density, gain and loss of the lasing mode as a function of anode current. The family of k.p gain and spontaneous emission spectra are shown at the sub-threshold point of micro Amps, near threshold, and above threshold. Flattening of the electrostatic potential across the active region above threshold reduces the energy differences between states localized in different wells. This effect is clearly seen by comparing the valence bands at the sub-threshold and above threshold points. The 2D plots optical intensity above threshold show the spatial profile of the lasing mode.

To load and run this example, select the Load button in DeckBuild > Examples. This will copy the input file and any support files to your current working directory. Select the Run button in DeckBuild to execute the example.