Surface Modification And Photoelectric Properties Of Al-based Thin Films For Organic Photodetectors

With the in-depth research on organic optoelectronic devices and the continuous development of MEMS device technology,the integration of organic photosensitive arrays and CMOS readout circuits to fabricate organic photodetectors（OPDs）is an important development direction in the field of organic optoelectronic devices.Compared with inorganic photodetectors,organic photodetectors have the advantages of wider spectral response range and strong designability of organic materials,which have great application value in imaging,detection,communication and other fields.At present,most of the research focus is on OPD devices based on ITO transparent bottom electrode structure.However,due to the process compatibility of CMOS readout circuits,the traditional ITO transparent bottom electrode is difficult to be used as the bottom electrode of the monolithically integrated OPD.In order to promote the development process of organic optoelectronic technology and readout circuit integration,the development of devices with new bottom electrode material structures is of great value to promote the development of monolithic integrated OPD technology.In this thesis,Al thin film compatible with CMOS process is selected as the main material of the bottom electrode,and the effect of the material of the surface modification layer of the bottom electrode on the performance of the OPD device is explored.The main research contents of the paper are as follows:（1）The optoelectronic properties of Al bottom electrode OPD devices and traditional ITO bottom electrode OPD devices were compared.Under the irradiation of a light source with a wavelength of 650 nm,the specific detectivity of the OPD device based on the Al bottom electrode structure can reach 4.52×10¹¹ Jones,which is lower than that of the OPD device with the classical ITO bottom electrode structure(7.55×10¹² Jones).Al is easily oxidized in air.The OPD device with Al bottom electrode structure was placed in air for32 hours,the specific detectivity of the device decreased from 4.52×10¹¹ Jones to3.2×10¹⁰ Jones due to the oxidation of Al.（2）Based on the OPD device with Al bottom electrode structure,a layer of Ti film was deposited on the surface of Al bottom electrode film as a modified layer.The effects of different thickness of Ti film modified layer（20,40,60 and 80 nm）on the performance of OPD device with Al/Ti double bottom electrode structure were studied.When the thickness of the Ti film is 40 nm,the specific detectivity of the device reaches 4.4×10¹¹Jones.At the same time,the device has a-3 dB cut-off frequency of up to 120.1 kHz and a linear dynamic range of up to 80 dB.More importantly,after being placed in air for 32hours,the performance of the OPD device with the Al/Ti double-layer bottom electrode structure did not deteriorate significantly,and the specific detectivity remained at4.4×10¹¹ Jones.（3）Based on the OPD device with Al/Ti double-layer bottom electrode structure,metal vanadium which theoretical work function value is close to that of metal titanium is selected to replace the Ti film as the modification layer,and the OPD device performance of the Al/V double-layer bottom electrode structure is studied.In the actual preparation process,the work function of the Al/V double-layer bottom electrode reaches-4.66 eV,which is quite different from the theoretical work function of V of-4.3 eV.The specific detection ratio of the device is 2.1×10¹¹ Jones,the-3 dB cut-off frequency can reach 66.6 kHz,and the linear dynamic range can reach 77 dB.