Intermixing in InP-based Quantum Well Photonic Structures Induced by the Dry-Etching Process: a Spectral Imaging Cathodoluminescence Study

Ridge waveguides in InP-based heterostructures were fabricated by inductively coupled plasma (ICP) reactive ion etching using chlorine-based gases. The heterostructures included a series of 6 quantum wells (QW) made from quaternary material GaxIn1-xAsyP1-y emitting at 1.55 mu m, and located very close to the surface (first QW at 300 nm). The etched structures (different widths and depths) were characterized at room and low temperature (80 K) by spectrum image cathodoluminescence (CL). The signature of the QWs was used to investigate effects induced by the dry etching process. Defects (or defect complexes) were observed, especially close to the edges of the etched structures, as well as a blue-shift of the CL lines from the nominal position. This was attributed to some intermixing of the QWs. Intermixing is induced by the defects that form during the dry etching process. The origin of these defects is discussed, taking into account previous studies performed on similar samples, except for the fact that the etched material was bulk InP instead of QW layers.