Investigation the performance of hydrogen peroxide pretreatment ZnO UV photodetectors using plasma-enhanced atomic layer
deposition
Yu-Chang Lin and Hsin-Ying Lee*
Department of Photonics, National Cheng Kung University, 701 Tainan, Taiwan, Republic of China
*Tel: 886-6-2082368 Fax: 886-6-2082368 E-mail: hylee@ee.ncku.edu.tw
Abstract− The ZnO films were deposited using a plasma-enhanced atomic layer deposition (PE-ALD) system and applied to metal-semiconductor-metal ultraviolet photodetectors (MSM-UPDs) as an active layer. In chemisorption of the ALD system at early cycles, the hydroxyl (OH) group on the initial substrate surface was necessary for the reaction with diethylzinc (DEZn). To improve the quality of the ZnO films and further enhanced the performance of the ZnO MSM-UPDs, the sapphire substrates were pretreated by hydrogen peroxide (H2O2) to increase the chemical bonding between ZnO film and substrate prior to the deposition. According to the X-ray photoelectron spectroscopy (XPS) analysis at the binding energy of 530.4 eV and 1021.6 eV in O 1s and Zn 2p orbit, the ZnO films exhibited the strongest Zn-O bonds under the H2O2 pretreatment for 60 min. The results indicated that H2O2 pretreatment effectively made more nucleation opportunity on the initial surface of the substrate to create more Zn-O bonds. Besides, the dark current of the ZnO MSM-UPDs without and with H2O2 pretreatment for 60 min operated at a bias voltage of 5 V was 3.64 μA and 0.27 μA, respectively. Since the better structural property and bonding condition caused the reduction of defects, the dark current was improved. In addition, the UV-visible rejection ratio (R365/R450) of the ZnO MSM-UPDs with H2O2 pretreatment for 60 min increased from 6.32×102 to 1.06×103 in comparison with the ZnO MSM-UPDs without H2O2 pretreatment.
