Investigation of performance improvement for ZnO-based ultraviolet photodetectors using plasma-enhanced atomic layer deposition system

Abstract

In this dissertation zinc oxide (ZnO) films were deposited on sapphire substrates by using a plasma-enhanced atomic layer deposition (PE-ALD) system Before the ZnO films deposition a hydrogen peroxide (H2O2) pretreatment technique was used to increase the nucleation opportunity on the initial sapphire surface which enhanced the quality of the deposited ZnO films Furthermore X-ray diffraction spectroscopy was conducted and the results revealed that the crystallinity of the ZnO films was considerably enhanced and that the (002) diffraction peak demonstrated the strongest intensity for the film subjected to H2O2 pretreatment for 60 min In addition X-ray photoelectron spectroscopy was executed and the results indicated that a high number of Zn-O bonds was generated in ZnO films pretreated appropriately with H2O2 The ZnO film deposited on a sapphire substrate with H2O2 pretreatment for 60 min was applied to metal-semiconductor-metal ultraviolet photodetectors (MSM-UPDs) as an active layer The dark current and ultraviolet–visible rejection ratio of the fabricated ZnO MSM-UPDs were improved to 0 27 μA and 1 06 × 10^3 respectively A plasma-enhanced atomic layer deposition system was also used to deposit magnesium zinc oxide (MgxZn1?xO) films with various Mg contents (x) Correspondingly the Mg content in the MgxZn1-xO films characterized using an energy dispersive spectrometer was 0 10 0 13 and 0 16 respectively The optical bandgap of the MgxZn1-xO films increased from 3 56 eV to 3 66 eV with an increase in Mg content from 0 10 to 0 16 The peak position of photoresponsivity for the MgxZn1-xO MSM-UPDs was also shifted from 350 nm to 340 nm The UV-visible rejection ratios of the MgxZn1-xO MSM-UPDs were higher than three orders of magnitude In addition excellent detectivity and noise equivalent power for the MgxZn1-xO MSM-UPDs were observed at a bias voltage of 5 V Finally the ultrathin alumina (Al2O3) inserted layer was applied to MgZnO MSM-UPDs The ultrathin Al2O3 inserted layer as an insulating layer effectively blocked leakage current and the dark current of the MgZnO MSM-UPDs was decrease from 1 nA to 0 34 nA with the thickness of the ultrathin Al2O3 layer increased from 0 nm to 5 nm Furthermore the noise equivalent power and detectivity of the MgZnO MSM-UPDs with 5-nm-thick Al2O3 inserted layer improved to 0 93×10^-14 W and 3 40?×?10^13 cmHz^1/2W^-1 respectively

Date of Award	2016 Aug 8
Original language	English
Supervisor	Hsin-Ying Lee (Supervisor)