The self-consistent simulation of carrier transport and its effect on the modulation response in semiconductor quantum well lasers

Abstract

A fully two-dimensional self-consistent quantum well laser simulator called Minilase has been developed. Both the optical and electronic device equations that describe a laser diode are discussed in detail. The dark and radiative recombination processes and the carrier transport mechanisms included in the simulator are first presented. Carrier transport in bulk regions of the device is modeled with drift-diffusion theory, and carrier fluxes at abrupt heterojunctions are treated with ballistic transport derived from thermionic emission theory. In addition, the first treatment of carrier capture in a quantum well laser simulator is presented, and a net capture rate is derived.

The methods used to solve the device equations are also discussed in detail. Since the simulation of quantum well lasers is a multiscale problem, a mesh of discrete points must be carefully generated to adequately resolve the device. Also, carrier transport at hetero-junctions and the injection of carriers into the quantum well require new discretization schemes not found in other electron device simulators.

Finally, modulation responses calculated with Minilase are studied. A direct comparison with experiment shows excellent agreement between the simulation results and measured data. The simulator is further used to explain the causes of gain saturation and low-frequency roll-off and to explore design variations that improve the modulation bandwidth. The study of the modulation responses confirms that, for the first time, the most significant carrier transport mechanisms have been incorporated into a quantum well laser simulator.