Improved performance of photoconductive gain hybrid UV detector by trap state engineering of ZnO nanoparticles

Abstract

With the purpose of examining the impact of donor polymer on the performance of nanocomposite photodetectors (PDs) and to better understand the underlying physics, different wide-bandgap semiconducting polymers, poly(N-vinylcarbazole), poly(9, 9-di-n-octylfluorenyl-2, 7-diyl) , and [9,9′-dioctyl-fluorene-2,7-diyl]-copoly[diphenyl-p-tolyl-amine-4,4′-diyl] (BFE), are mixed with ZnO nanoparticles (NPs) to fabricate hybrid UV PDs. Three different polymer matrix nanocomposites were investigated that differ in the electron-trap depth in the nanocomposite and also the carrier tunneling energy at the interface. All the fabricated PDs exhibit strong photoconductive gain characteristics which can be attributed to trapped electron accumulation and band bending at the cathode interface. Experimental results show that the manipulation of the photoactive nanocomposite improves the PD properties simultaneously, namely, the external quantum efficiency (EQE, ∼104%), the maximum detectivity (D*, ∼1013 Jones), and the linear dynamic range (LDR, ∼85 dB). In addition, the gain bandwidth product of the device improves more than 50 times. Furthermore, the effect of the photogenerated carrier profile within the active layer is investigated experimentally by changing the direction of the incident light using a transparent cathode. Interestingly, under illumination through the Al cathode, faster photocurrent response, wider spectral range toward the deep UV region, and higher EQE in relatively low voltages are observed. These considerations might provide a general strategy to fabricate low-cost photoconductive PDs with a reasonably good combination of gain, response speed, LDR, and selectivity.