Disclosing the structure of Multi-Quantum Wells in Electroabsorption-Modulated Lasers by using synchrotron radiation X-ray microprobe

In the last years strong efforts have been devoted to improve the frequency of optical fibre communications and to achieve this goal the monolithic integration of different functions at chip level is required. The most promising device fulfilling this requirement is the Electro-absorption Modulated Laser (EML) which is realized using the Selective Area Growth (SAG) technique and is based on a Multiple Quantum Well (MQW) Distributed Feedback Laser monolithically integrated with an MQW Electro Absorption Modulator. Optimization of the growth parameters is carried out by empirical approaches as direct structural characterization of the MQW is not possible with laboratory X-ray sources, owing to the micrometer-variation of composition and thickness inherent to the SAG technique. Exploiting the X-ray microbeam available at the ESRF ID22 beamline we performed a combined μm-resolved XRD, XRF and EXAFS study. directly on a MQW EML device of industrial interest realized by Avago Technologies. This investigation, coupled with the μm-resolved determination of the energy gap by PL, allowed us to fully determine the relevant parameters of the growth (i.e. well and barrier widths and mismatches). New generations of devices may arise from the information obtained from this unprecedented characterization approach.