Interdigitated photodetectors (IPDs) based on the twodimensional electron gas (2DEG) at the AlGaN/GaN interface have gained prominence as high sensitivity ultraviolet (UV) PDs due to their excellent optoelectronic performance. However, most 2DEG-IPDs have been built on rigid substrates, thus limiting the use of 2DEG-IPDs in flexible and wearable applications. In this paper, we have demonstrated high performance flexible AlGaN/GaN 2DEG-IPDs using AlGaN/GaN 2DEG heterostructure membranes created from 8 in. AlGaN/GaN on insulator (AlGaN/GaNOI) substrates. The interdigitated AlGaN/GaN heterostructure has been engineered to reduce dark current by disconnecting the conductive channel at the heterostructure interface. Photocurrent has been also boosted by the escaped carriers from the 2DEG layer. Therefore, the utilization of a 2DEG layer in transferrable AlGaN/ GaN heterostructure membranes offers great promises for high performance flexible 2DEG-IPDs for advanced UV detection systems that are critically important in myriad biomedical and environmental applications.

We have demonstrated flexible GeSn metal-semiconductor-metal (MSM) photodetectors (PDs) by exploring the effect of mechanical strain on its optoelectronic properties. The PDs were fabricated from transfer-printed GeSn nanomembranes on polyethylene...

G. (2020). Strain-free GeSn nanomembranes enabled by transfer-printing techniques for advanced optoelectronic applications. Nanotechnology, 31(44), 445301-.

We have demonstrated high-performance flexible germanium (Ge) vertical p−i−n photodetectors (PDs) based on a resonant cavity structure by a direct flip transfer of Ge nanomembranes on polyethylene terephthalate (PET) substrates. Finite-difference time-domain simulation proves that the vertical cavity structure composed of the bottom gold and top SU-8 layers as a reflector and an anti-reflection surface, respectively, could enhance the average absorption in the near-infrared (NIR) region (i.e., 1520−1640 nm) from 0.06 to 0.20 by 233%. Strains introduced into Ge NMs by convex and concave fixtures are measured to be 0.37 and −0.32%, respectively. The fabricated PDs exhibit a low dark current density of 9.6 mA/cm 2 at −1 V and a high forward−reverse current ratio of 10 5 under the flat condition. Responsivity at 1550 nm increases from 52.5 to 133.8 mA/W by tensile strain, while it slightly decreases to 32.6 mA/W under comparable compressive strain. Furthermore, the devices show no degradation in their optoelectronic responses after 200 bending cycles at convex fixtures with a radius of 30 mm. Overall, such flexible Ge PDs with the capabilities of both excellent optoelectronic performance and mechanical durability represent significant advances in the field of group IV NIR optoelectronic devices.

We report an enhanced performance of flexible titanium nitride/germanium-tin (TiN/GeSn) photodetectors (PDs) with an extended photodetection range based on sub-bandgap absorption. Single-crystalline GeSn membranes transfer-printed on poly­(ethylene terephthalate) are integrated with plasmonic TiN to form a TiN/GeSn heterojunction. Formation of the heterojunction creates a Schottky contact between the TiN and GeSn. A Schottky barrier height of 0.49 eV extends the photodetection wavelength to 2530 nm and further enhances the light absorption capability within the detection range. In addition, finite-difference time-domain simulation proves that the integration of TiN and GeSn could enhance average absorption from 0.13 to 0.33 in the near-infrared (NIR) region (e.g., 1400–2000 nm) and more than 70% of light is absorbed in TiN. The responsivity of the fabricated TiN/GeSn PDs is increased from 30 to 148.5 mA W–1 at 1550 nm. There is also an ∼180 nm extension in the optical absorption wavelength of the flexible TiN/GeSn PD. The enhanced performance of the device is attributed to the absorption and separation of plasmonic hot carriers via TiN and the TiN/GeSn junction, respectively. The effect of external uniaxial strain is also investigated. A tensile strain of 0.3% could further increase the responsivity from 148.5 to 218 mA W–1, while it is decreased to 102 mA W–1 by 0.25% compressive strain. In addition, the devices maintain stable performance after multiple and long bending cycles. Our results provide a robust and cost-effective method to extend the NIR photodetection capability of flexible group IV PDs.