Muhammad A. Alam

Role of p-doping profile in InGaAsP multiquantum well lasers: comparison of simulation and experiment

We study the role of p-doping on the characteristics of InGaAsP/InP multi-quantum well lasers through detailed simulations and experiments. The static and dynamic characteristics of a series of 1.3 μm lasers with varying p-i junction placement were measured. The device characteristics were simulated including carrier transport, capture of carriers into the quantum wells, quantum mechanical calculation of the levels and optical gain in the wells and solution for the optical mode. The simulations were self consistent and carried out as a function of device bias. The simulations account for the trends observed with p-doping profile. In particular, the simulated optical gain and small signal resonance frequencies agree well with the measurements. The trend of larger resonance frequency with increased p-doping in the active layer of the laser depends on both the gain and the carrier transport through the multi-quantum well region.

Simulation of semiconductor quantum well lasers

A 2D bulk and quantum well laser simulation tool, based on the Bell Laboratories electron device simulator PADRE, has been developed. PADRE contains a suite of robust programs for obtaining self-consistent solutions of the Drift Diffusion equations. To this suite has been added programs for calculating the optical intensity inside the laser, the capture and emission rates between bound and free carriers, the interaction between the confined carriers and the optical field, and a set of ne, powerful schemes for obtaining rapid convergence of the nonlinear equations of the model. This paper describes the augmented program in its present form, gives examples of its present abilities and limitations, and discusses some illustrative results to show features of the simulation tool.

Simulation of carrier dynamics in multiple-quantum-well lasers

We study the impact of carrier dynamics on the characteristics of InGaAsP/InP multi-quantum well lasers through detailed simulations and experiments. The device characteristics were simulated including carrier transport, capture of carriers into the quantum wells, quantum mechanical calculation of the levels and optical gain in the wells and solution for the optical mode. The simulations were self consistent for each value of device bias. The device characteristics studied include static light-current-voltage curves, dynamic small signal impedance and the small signal modulation of the light output. The comparison between simulation and experiment constrains the capture rate for these devices. The simulations suggest that the modulation response of these devices is not fundamentally limited by the carrier transport for the frequency range studied. The trends are understood in terms of sequential transport through the multi-quantum well active region.

Role of nonequilibrium carrier distributions in multiple quantum well InGaAsP-based lasers

A microscopic model for the operation of multi-quantum well laser diodes is described. It includes bulk transport of carriers modeled by drift-diffusion equations, confined carriers in the quantum wells modeled by the Schroedinger equation, photon modes modeled by a Helmholtz equation and couplings described by rate equations. Application of this model shows that the carrier distribution in the active layer of the laser can not be described by quasi-equilibrium conditions. One consequence is the substantially non-uniform distribution of carriers among the quantum wells when the laser is biased above threshold. Another consequence is the observation of photoluminescence in wide area devices under short circuit conditions.

Comprehensive simulation of quantum well lasers

We demonstrate a simulation tool which treats a full two dimensional cross section of a semiconductor laser diode with multiple quantum wells in the active region. The free carrier transport, the bound quantum well populations, the capture of carriers into the quantum wells, the gain and spontaneous emission, the transverse optical mode and the photon mode population are all treated in a fully coupled and self-consistent solution for each bias of the laser diode. The simulations are illustrated for an EMBH laser structure with seven quantum wells in the active region.

Process simulation of selective-area MOCVD growth for optoelectronic integrated circuits

MOCVD selective area growth is a simple and versatile process technique widely used in the fabrication of optical integrated circuits. A computational model for selective area growth is verified using a comprehensive suite of experimental measurements: atomic force microscopy, optical interference microscopy, micro-photoluminescence, and micro-Xray diffraction. The model then allows for constructive engineering of the material thickness and composition through manipulation of the oxide mask used in selective area growth. Examples demonstrating the accuracy of the model and its applicability to device design are provided.