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Harold

A hetero-structure laser diode model

Simulations

Harold Simulations

A HAROLD device simulation consists of solving the governing equations of the model at a set of bias currents, so as to obtain the characteristics of the device vs. current.

HAROLD has a number of simulation modes to choose from:

  • Running mode

  • 1D: Solves self-consistently the various differential equations of the model in the vertical (y) direction only, assuming uniformity on the longitudinal (z) direction.

  • 2D: Solves self-consistently same equations as in 1D mode but also considers longitudinal effects such as surface recombination and optical absorption at facets, and the non-uniformity of the optical field.

  • PICWave Model: a variation of the 1D isothermal model, this mode is used for producing material gain models which can be exported to PICWave.

  • Execution mode

  • Isothermal: Simulates the device under “pulsed” operation i.e. ignores heating such that the temperature is fixed at a constant value throughout the whole structure.

  • Self-heating: Simulates the device under “CW” operation i.e. accounts for device heating model the heatflow within the device

  • Test: A quick diagnostic mode which simulates the device at zero bias - it allows you examine basic results so you check that your layer structure has been set up as intended.

Simulation Results

Due to its detailed physical model, HAROLD can obtain a wide range of simulation results, including:

  • 1D/2D Results (i.e. vertical/vertical-longitudinal profiles):

  • Electrostatic potential, electric field

  • Electron and hole Fermi energies

  • Conduction and valence band edges

  • Electron and hole densities (in bulk and QWs)

  • Electron and hole current densities

  • Recombination rates: SRH, Auger, spontaneous emission, stimulated

  • Heat flow and temperature profiles, profiles of different heat sources (Joule effect, non-radiative recombination, free-carrier absorption)

Alignment of electron and hole Fermi energies with conduction and valence bands

(left) Alignment of electron and hole Fermi energies with conduction and valence bands in
InGaAsP 1.55µm 6QW epi-structure and (right) profile of confined and unconfined electron and
hole densities in same structure – vertical leakage of unconfined carriers through QWs can be seen

  • Per-bias Results (i.e. vs. bias current/voltage/current density):/p>

  • Optical powers for left and right-hand facets (optical output power, scattered and absorbed power)

  • Dissipated power due to Joule heating, non-radiative recombination, free carrier absorption

  • External slope efficiency for both facets (dP/dI)

  • Electron and hole densities (in bulk and QWs)

  • Active region temperature

  • Quantum efficiency

  • Lasing wavelength

  • Modal and material gain

  • Effective mode index change

  • Free carrier loss

  • Recombination rates (in bulk and QWs): SRH, Auger, spontaneous emission, stimulated

A comparison of the various recombination rates in a laser

(left) LI curves for self-heating laser diode simulation for ambient temperatures 0C to 100C
and (right) recombination rates for 50C ambient temperature simulation –
the rising Auger contributes to the thermal roll-over in the LI curve

  • Spectra (at maximum bias):

  • Gain

  • Spontaneous emission

  • Refractive index

Spectra

Gain (left) and spontaneous emission (right) spectra for the set of simulated biases (isothermal simulation)

  • Quantum well results:

  • Electron, light-hole, heavy-hole potentials

  • QQW wavefunctions and energy eigenvalues for electron, light-hole and heavy-hole sub-bands

Wavefunction of the lowest energy electron state in a 6 QW structure

Wavefunction of the lowest energy electron state in a 6 QW structure