Extraction of GeSn absorption coefficients from photodetector response

Germanium tin (GeSn) shifts the photo-response of infrared (IR) light detectors from a typical cutoff wavelength of Ge detectors of 1550nm toward the mid infrared (MIR) [1]. The determination of the optical absorption coefficient of GeSn is difficult because it requires both high grade GeSn material and appropriate measurement structure. A series of vertical pin photodetector with the absorber material GeSn of excellent quality were fabricated achieving quantitative extraction of the absorption coefficient from photo-response. In this paper the fabrication of vertical GeSn photodetectors, the measurement of the background doping level in the intrinsic region (i-region) and the determination of the absorption coefficient are presented and the influence of high doped contact layers and electro-absorption effects from the built-in electric field are discussed.