Thermal evaporation fabrication of UV-NIR p–i–n photodetectors based on highly tensile-strained Ge via incorporation of Pb rather than Sn and As

Abstract

Direct band gap strained germanium (Ge) is one of the promising materials that have been used in various applications in the last decades, with elements such as Sn, As, and Pb being used to modulate the Ge band gap. In this work, we compared the effect of the content of three metals (Sn, As, and Pb) on the Ge structure and optoelectronic properties and demonstrated the advantages of Pb content over Sn. We fabricated p–i–n based poly-Ge by Sn-, As-, and Pb-induced crystallization of thermally deposited Ge annealed at 400 °C under vacuum. Raman spectroscopy and X-ray diffraction were used to investigate the impact of the incorporation of metals on the strain in the Ge network. We investigated the direct transition of the prepared samples using UV-Vis-NIR spectroscopy and photoluminescence. We measured the charge carrier lifetime using time-resolved PL. We investigated the diode quality and dark current using I–V characteristics in dark conditions. Photoresponsivity measurements were performed to measure the spectral response of the prepared junctions. The results reveal that the GePb-based p–i–n junction has a higher tensile strain than GeAs and GeSn. GePb has many direct transitions in the UV, NIR, and mid-IR regions of the spectra. GePb has a longer carrier lifetime than GeSn and a low dark current and a quality factor near the ideal value compared to the other prepared junctions. The fabricated GePb-based photodetector (PD) has a higher responsivity in the UV and NIR regions compared to GeSn- and GeAs-based PDs. This makes the fabricated GePb-based PD more suitable than GeSn for photodetection applications in multiple regions of the spectrum.