Cathodoluminescence-integrated electron microscopy for failure analysis of long-wave ridge waveguide quantum cascade lasers

Abstract

This work presents the refined implementation of a previously developed electron microscopy characterization process for analyzing the propagation of defects within quantum cascade lasers (QCLs) as they relate to device degradation and eventual failure during continuous-wave operation. Electron microscopy techniques such as scanning electron microscopy and transmission electron microscopy are used to isolate the presence of defect nucleation sites within a set of ridge waveguide QCLs emitting in the long-wave infrared range. In addition to these methods, the use of cathodoluminescence as a standout tool for the localization and characterization of dislocations is demonstrated for QCLs. The method is illustrated through a defect density analysis of different QCL wafers grown on lattice mismatched substrates. It is then implemented as an intermediate step in the damage analysis, where it serves a dual purpose of characterizing the propagation of crystalline defects in the QCL cladding for a large field of view, while also providing information which allows for more informed lamella extraction for subsequent TEM imaging. The observed defect sites are detected across a range of devices, from healthy baseline devices to those exhibiting sub-par performance and failure. The primary defect in these samples is observed to result from delamination between the SiN and InP interface in the ridge waveguide, creating large discontinuities within the active region and contributing to device degradation and failure.