Dependence of Threshold Current Density on the Waveguide Ridge Width in Quantum-Cascade Lasers

We make a systematic study to find the dependence of the threshold current density of a mid-infrared quantum-cascade laser on the waveguide ridge width. The optical and thermal parameters of the waveguide are calculated with a finite-element method, and gain is found from a self-consistent rate equation model with energy-balance. The results show the existence of an optimal ridge width that minimizes the threshold current density of the laser. The influence of the interface roughness parameters on laser performance is also discussed.

I. Introduction

Quantum cascade lasers (QCLs), based on intersubband transitions between the conduction subbands in multilayer periodic semiconductor structures embedded in waveguide resonators, have undergone tremendous and continuous progress since their launch in 1994 [1]. Numerous aspects of these structures are still being investigated by various, even more sophisticated modeling methods. These include electron transport and optical gain modeling, e.g., [2]–[6], waveguide optimization [7], thermal management [8]–[10], etc.