The addition of a thick insulating layer (I) between the semiconductor (S) layer and the metal (M) electrodes in a conventional MSM photodetector induces a differential photoresponse due to capacitive charging/discharging of the insulator layer by the photo-induced polarization of the active semiconductor layer in the MISM device.[1] The magnitude of the photoresponse in such differential photodetectors can be greatly enhanced by using high-k electrolytic insulator layers (I'), such as ionic liquids, through the strong influence of the highly energetic SI' interface on charge separation and stabilization. The move towards liquid insulating systems not only allows direct illumination of the active layer without the need for transparent electrode contacts, but also extends the choice of photoactive materials to include biomolecules, which benefit from a fluid environment.[2] Upon further insertion of a low-k polymer dielectric (I") at the opposite MS contact, yielding a “floating” photoactive layer, the resultant MI'SI"M architecture ensures purely non-Faradaic operation, and allows the responsivity and bandwidth to be mutually improved, thereby breaking the responsivity-bandwidth trade-off that limits the MISM architecture.[3]
In this seminar, I will focus on our recent results in differential photodetection utilizing organic, biological and, more recently, inorganic active layer materials, including viable strategies for their optimization and their applicability for motion detection. Furthermore, using a number of examples, their merits as an analytical tool for the characterization of (novel) (bio)materials will be discussed. Amongst those, I will present our recent results into the use of 3 microbial rhodopsin proteins in such MISM photodetectors - proteins, which are often regarded as the “eyes” of microbes, as they not only resemble the light receptors in our eyes in structure, but also undergo light-induced structural changes that can lead to signaling cascades within microbes to lead them toward favorable territories, or to the production of ATP (the unit of energy in a biological cell). Not only the device performance driven by the activation of such proteins by light, in terms of responsivity, bandwidth and signal stability will be discussed, but also what information we can gain through our studies under a range of conditions (temperature, pH, illumination wavelength), about the biomolecules themselves.
REFERENCES
[1] L. Reissig, S. Dalgleish, K. Awaga, AIP Adv. 6, 015306 (2016).
[2] S. Dalgleish, L. Reissig, Y. Sudo et al., Chem. Comm. 51, 16401 (2015).
[3] L. Reissig, S. Dalgleish, K. Awaga, Sci. Rep. 8, 15415 (2018).