Introduction of defects during the dry etching of InP photonic structures: a cathodo-luminescence study

Abstract

Introduction of point defects during the dry etching process of InP-based photonic structures has been investigated using the spectroscopic cathodo-luminescence (CL) technique. The measurements were performed on cleaved cross-sections from standard passive waveguides with rectangular shape, different widths, etched in bulk InP using either reactive ion etching (RIE) with CH4/H2 as the etching gases, or high density—inductively coupled plasma (ICP) etching with SiCl4. Etched depths up to 4 μm were reached. In the case of the ICP process, a defect-related band appears in the CL spectra, which is tentatively attributed to some kind of complex defect involving indium vacancies, because of its energy measured at low temperature. This band does not appear for the RIE process. In addition, local stress also occurs in the etched ridges (identified from the spectral shift of the band to band transitions), which seems to arise from the occurrence of the defects. The features on the spectroscopic CL images (both in terms of the defect band and the changes in intensity related to non-radiative recombination centers) are discussed based on the nature of the hard mask material used for the etching process and the local temperature reached during processing, especially with the high density ICP process.