Effect of hole blocking dielectric layer on microstructure and photoconducting properties of polycrystalline Se thin films
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We fabricated polycrystalline selenium (c-Se) based photodetectors using three different dielectrics (HfO2, Al2O3 and SiO2) as the hole blocking layer (HBL), and studied the influence of the HBLs on the photoconducting performance of the photodetectors. The microstructure of the c-Se layer is greatly influenced by the nucleation behavior of the tellurium (Te) adhesion layer deposited between the c-Se layer and the HBLs. The photoconducting performance of the photodetectors is basically dependent on the barrier height at the junctions of the HBL with the tin-doped indium oxide (ITO) anode and with the c-Se layer. A higher barrier height at the HBL/ITO junction leads to a lower dark current density (ID) of the photodetectors. However, the photodetector with the SiO2 HBL exhibits the largest ID as the bias exceeds 2 V although it has the highest junction barrier height. We attribute the abnormity to the rugged morphology of the c-Se layer, which is a result of a less dense Te nucleation on the SiO2 HBL. The photocurrent density (Iph) is inversely related to the junction barrier height at the HBL/c-Se contact. The c-Se photodetector with the HfO2 HBL has the largest IPh and the one with the SiO2 HBL has the smallest. The photodetector with the HfO2 HBL exhibits a quantum efficiency of ~ 89% at 6 V.
This study is supported by the Ministry of Science and Technology, R.O.C. under the contract number MOST 106-2221-E-009-075-MY2. The technical support of the National Nano Device Laboratories are also acknowledged.
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