Evidence of chlorine ion penetration in InP/InAsP quantum well structures during dry etching processes and effects of induced-defects on the electronic and structural behaviour

Abstract

In this work, the overall point of interest is the occurrence of artefacts associated with dry etching processes on InP-based structures. By artefacts we mean creation of defects in the remaining material after etching, defects which might be deleterious to both performance of the photonic devices being fabricated, and reliability/lifetime of these devices. A specific sample structure was defined on InP with InAsxP1−x quantum wells (QWs). These QWs are buried within 1μm from the surface, for maximum sensitivity to reactive species produced in the etch plasma, and are designed with a gradual As/P composition, such that the luminescence peak produced by each QW is clearly identified. These samples thus possess a “built-in” marker including its own scale. We focused on chemistries with chlorine (SiCl4/H2/Ar and Cl2/N2), implemented in an inductively coupled plasma reactor. With such chemistries, etch rates of 0.5μm/min can be reached.The samples are not really etched, but just exposed shortly to the plasma for the interaction to take place. Actually, we just etch at most a few tens of nanometers. Characterisation was carried out by spectrally-resolved cathodo-luminescence and photo-luminescence. We also measured secondary ion mass spectrometry profiles, which revealed the penetration of chlorine into the samples. High resolution transmission electron microscopy was used, to probe the crystal quality. By comparing doped and un-doped samples, we show that the chlorine observed after exposure consists at least partly in Cl− ions. The other important observation is some mechanical compressive stress, which is also a consequence of the local concentration of Cl impurities after exposure to the plasma.