Study of PVK buffer layer effects on the performance of n-ZnO/p-Cu2O thin film heterojunction photodetectors

Abstract

In this dissertation I investigate the effects of a poly-(N-vinylcarbazole) (PVK) intermediate layer on the performance of n-ZnO nanorods/p-Cu2O heterojunction photodiodes Polycrystalline p-Cu2O thin film was electrodeposited on a commercial available ITO/glass substrate An organic PVK layer was then spin-coated onto the Cu2O film followed by ZnO nanorods synthesis on a patterned ZnO seed layer using a chemical bath deposition (CBD) method The PVK layer acts as an electron blocking/hole transporting layer between the ZnO and the Cu2O films Meanwhile the ZnO/Cu2O heterojunction photodiodes without PVK layer was also fabricated for comparison A scanning electron microscope was used to observe the surface morphologies and cross-sectional images of the samples Crystalline phase and orientation were determined by x-ray diffraction patterns obtained from an x-ray diffractometer To analyze the role of PVK I measured the electrical and optical properties of the photodiodes Under UV light illumination the photocurrent/dark current ratios of the n-ZnO/PVK/p-Cu2O and n-ZnO/ p-Cu2O photodiodes at -0 5 V bias are 133 and 3 99 respectively The n-ZnO/p-Cu2O exhibits a UV-to-visible rejection ratio (R-360nm/R-450nm) of approximately 1 735 under a -0 5V bias When the PVK buffer layer is inserted between the n-ZnO and the p-Cu2O layers the rejection ratio increase to 350 owing to higher UV photocurrent/dark current contrast ratio and lower photocurrent generation under visible light illumination On the basis of above results several novel features have been demonstrated for the first time: (a) UV photo-generated holes can effectively transmit through the PVK layer to the p-Cu2O layer; (b) insertion of a PVK buffer layer significantly minimize the reversed-bias leakage current which leads to a large amplification of the photocurrent; and (c) the device with a PVK buffer layer can improve UV-visible responsivity ratio and achieves better UV detection sensitivity

Date of Award	2015 Jul 15
Original language	English
Supervisor	Dung-Ching Perng (Supervisor)