The demonstration of a CMOS compatible laser working at room temperature has been eagerly sought since the beginning of silicon photonics. Although bulk Germanium (Ge) is an indirect bandgap material, Tin (Sn) can be incorporated into it to turn the resulting alloy into a direct band-gap semiconductor. Recently, lasing was demonstrated at cryogenic temperatures using thick GeSn layers with Sn contents of 8.5% and above. Optical micro-cavities were later added to reduce the laser threshold. Here, an under-etching of thick GeSn layers selectively with regard to Ge confines optical modes and relaxes the compressive strain built inside the layers, resulting in more direct band-gaps behavior. Such photonic components rely on technological processes dedicated to GeSn. In this paper, we present our recent developments on (i) anisotropic etching of GeSn and (ii) isotropic etching of Ge selective with regard to GeSn. Even for GeSn with a Sn content as low as 6%, the etching selectivity is of 57. For 8% Sn content, the selectivity reaches 433. We used these processes to fabricate micro-disk optical cavities in thick GeSn layers. Under continuous wave pumping, optical modes were detected from photoluminescence spectra.
L. Milord, J. Aubin, A. Gassenq, S. Tardif, K. Guilloy, N. Pauc, J. Rothman, A. Chelnokov, J. M. Hartmann, V. Calvo, and V. Reboud, "Inductively coupled plasma etching of germanium tin for the fabrication of photonic components," Proc. SPIE 10108, Silicon Photonics XII, 101080C (Presented at SPIE OPTO: January 30, 2017; Published: 20 February 2017); https://doi.org/10.1117/12.2252280.
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