Qiuming Yu1
Cornell University1
Photodetectors have a wide variety of applications in modern technology, and new ones are constantly arising. Therefore, it is highly desirable to be able to design devices quickly and cheaply<b>. </b>Traditional design process starts with making decisions and optimizing them to meet application needs. Inverse design offers promising approach for expediting design by starting with application criteria<b>. </b>Either way, the toolbox must be thoroughly understood and generalizable to different materials, spectral ranges, and devices<b>. </b>In this talk, I will cover our recent work on the development of photodetection toolbox to achieve sensitive, low driving-force, narrowband UV photodetectors. Our UV photodetectors are based on the photodiode structure. To enhance the photodetection sensitivity or to increase the specific detectivity of UV photodetectors, we vary the ratio of p-type conjugated polymer to n-type fullerene electron acceptor and control the photoactive layer morphology to achieve electron-trapping induced band bending and charge injection, and hence inducing the photomultiplication effect to gain the external quantum efficiency much higher than unit. Similar strategy can be applied to the polymer-ZnO nanoparticle nanocomposite system to utilize trapped electrons in ZnO nanoparticles to realize the photomultiplication effect. Additionally, by controlling and utilizing charge generation, separation and transport in the hole-only photodiode devices, we can achieve narrowband, photomultiplication, low-driving force UV photodetectors. Another strategy to achieve the narrowband photodetection is through the charge-collection narrowing by on purpose increase the thickness of the active layer to allow the selective detection of photons at the long-wavelength absorption edge. Considering the function of manipulating light absorption and confining electromagnetic energy into the nanoscale volume, we integrate aluminum plasmonic nanostructures into the photodiode to manipulate the UV photodetection. We can ether place the aluminum nanohole arrays on top of a glass substrate to replace the ITO layer as a transparent electrode or embed aluminum nano-hemisphere arrays into the top aluminum electrode to achieve the bias-dependent photoresponses and enhanced photosensitivity. All these developments are aided by the finite-difference time domain (FDTD) simulations, transfer matrix method (TMM) optical calculations, and experimental studies to understand the charge generation, separation, transport, and recombination in the devices. Our work highlights the importance to correlate the device internal physical processes to the design inputs and the sensing capabilities in order to achieve the desired photodetection.