Fabrication And Characterization Of Ultraviolet Photodetectors Based On MgZnO And Organic Hole Transport Materials

Ultraviolet (UV) photodetectors (PDs) have drawn much attentions due to their applications in various area, such as environment monitoring, flame detection, missile warning and space to space transmission. During the inorganic materials for UV detection, MgZnO has been studied extensively in recent years for its tunable wide-band gap. However, the lack of reliable p-type MgZnO hinders any p-n junction based optoelectronics devices. Recently, organic UV PDs developed rapidly since its simplicity in fabrication, low cost and high performance. However, compared with the electron transport materials, the hole transport materials have much higher carrier mobility. To find suitable electron transport materials for UV OPD is a challenge.In this work, we choose the MgZnO thin film as the electron transport material with the organic hole transport materials to fabricate the UV PDs. By optimizing the grown condition of the films and structure of the devices, we got high performance UV PDs. The main results are as follows:1. The MgZnO/NPB heterojunction PDs were fabricated on ITO quartz substrates. In order to optimize the performance of the device, different thickness of NPB thin films were grown. It shows that the device has high performance, when the NPB film is 70 nm. A narrow band photoresponse was observed from 300 to 400 nm. The maximum peak response is at 340 nm, which is 0.192 A/w at the bias of-1 V. The PD has a high photo-to-dark ratio of 1×105 at-2 V and a high detectivity of 5.3×1012 cmHz1/2W-1, the dvice is sensitive for UV-A light.2. The MgZnO/PVK heterojunction PDs were fabricated on ITO quartz substrates. The effect of the thickness of MgZnO layer and PVK layer was investigated. The results indicate that the dark current is decreasing and the photo-to-dark ratio is increasing as the increasing thickness of MgZnO layer. When we keep the thickness of MgZnO layer unchanging (150 nm), the performance of the device shows a trend first increase and then decrease as the increase of thickness of PVK layer. The device has the best performance, when the PVK is 60 nm. The device is a visible-blind detector, the response peak is at 346 nm, which is 0.114 A/W. The PD has a high photo-to-dark ratio of 4.4×102 at-2 V and a high detectivity of 2.9×1011 cmHz1/2W-1.3. The MgZnO/PEDOT:PSS Schottky PDs with two structures were fabricated. The results indicate that the device with PEDOT:PSS as the transparent electrode has higher performance than the one with ITO electrode. The device has a wide-band photoresponse, the response peak is at 340 nm, which is 0.156 A/W and it’s sensitive for UV-B light. The idea factor and Schottky barrier height is 1.5 and 0.72 eV.4. The MgZnO/TAPC heterojunction PDs were fabricated on quartz substrate by using ITO and PEDOT:PSS as the transparent electrode. The detection performance of the devices was also investigated. The device with PEDOT:PSS electrode has better performance than the device with ITO electrode. The PD has a wide-band response, the response region is from 200 nm to 360 nm. Two response peak of the device have been observed, which is 0.159 A/W at 314 nm and 0.147 A/W at 247 nm. The detectivity of PD is 1.2×1011 cmHz1/2W-1 and 1.12×1011 cmHz1/2W-1.