Modulation of light absorption in flexible GeSn metal-semiconductor-metal photodetectors by mechanical bending

We have demonstrated flexible GeSn metal-semiconductor-metal (MSM) photodetectors (PDs) by exploring the effect of mechanical strain on their optoelectronic properties. The PDs were fabricated from transfer-printed GeSn nanomembranes on polyethylene terephthalate (PET) substrates. Strain was introduced into the GeSn PDs under bend-down (uniaxial tensile strain) and bend-up (uniaxial compressive strain) conditions and their values were measured by Raman spectroscopy. The applied strain can affect the band-structure of the GeSn alloys, leading to a modulation of the electrical and optical characteristics of the PDs. Accordingly, dark current characteristics show an increase from 8.1 to 10.3 mu A under the bend-down conditions and a decrease to 7.2 mu A under the bend-up conditions, respectively. The optical responsivity at a wavelength of 2 mm increased by 151% under bend-down conditions, while it decreases by 35% under bend-up conditions. A theoretical study was carried out to support the fact that the responsivity enhancement is attributed to the change in the absorption coefficient of the strained GeSn. The results offer a new pathway to modulate the optical properties of GeSn for flexible applications.