Harold

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 (XY, option): as above but models variations of electrical and optical fields in both transverse directions.

• 2D (YZ): 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)

(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):

• 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

(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:

• Gain

• Spontaneous emission

• Refractive index

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