Nanocomposite Film Photodetector With Field-effect Transistor Configuration

In order to adapt the rapid development of information society, optoelectronic devices acting as the core of optical communication technology are getting miniaturized and integrated. In the promotion of nanotechnology, nanostructures with novel characteristics and advanced nanofabrication processes are both introduced into researches and applications of optoelectronic devices to accelerate their development. At the same time, nanophotonics further expands the depth of physics and application fields of optoelectronics technology. As an important member of nanostructured optoelectronic devices, the nanocomposite film photodetector combines the quantum effect and material advantages of nanofilms with the photoconductive effect of semiconductors effectively, and it has received much concern due to its excellent properties and wide application prospects. The nanocomposite film photodetector with field-effect transistor(FET) configuration can overcome the shortcomings of quick exciton quenching and low optical gain for conventional photodetectors, in this way, it can not only possess the excellent response properties but the function of signal amplification and easiness to be integrated. By introducing organic conjugated molecules with planar quantum dots properties into the nanocomposite film photodetector with FET configuration, it can not only achieve high carrier transport and enhanced the detecting performance, but also can simplify the fabrication processes, reduce the production cost, realize the flexible processing, and so on. It is significant for optoelectronic device to realize high-performance, miniaturization, flexible and mass production. In addition, quantum dots with tunable absorption range, large absorption coefficient, good stability, high output efficiency of carriers have been combined with organic conjugated molecules. By using both advantages and characteristics of them, organic/inorganic nanocomposite film photodetectors with excellent properties are fabricated, and they show a new development momentum for optoelectronic devices. Therefore, conjugate molecules and semiconductor quantum dots are tentatively used to fabricate new type photodetectors in this dissertation, and we hope it can open some exploratory works for researches and applications of photodetectors in the future.In this dissertation, the nanocomposite film photodetector with FET configuration is taken as the thesis object, and different nanocomposite photodetectors with FET configurations were fabricated through simple methods like spin-coating and vacuum evaporation. Electrical and detecting performances of the devices were characterized in specific spectral response ranges, and influential factors of the device performances were analyzed. The main research results can be summarized as follows:(1) Common planar bottom-gate top-contact FET configuration was chosen to fabricate FET-based pentacene photodetectors ITO(G)/PMMA/Pentacene/Au(S,D) with PMMA dielectric layer thicknesses of 230 nm, 520 nm and 800 nm, respectively. Π-conjugated pentacene nanofilm was chosen as the active layer due to its excellent electrical characteristics of FET and its high absorbance in the full visible region. Polymethylmethacrylate(PMMA) nanofilm was selected as the dielectric layer due to its low cost, simple preparation and high transmittance. The electrical properties of the devices were characterized, and the detecting properties were investigated in the full visible region from 350 nm to 750 nm. The influence of the PMMA dielectric layer thickness on device performance was discussed, and FET-based pentacene nanofilm-photodetectors with 520 nm moderate PMMA layer had shown the best photosensitivity, responsivity, and wavelength selectivity after optimization.(2) The vertical FET-based pentacene nanofilm photodetector ITO(S)/Pentacene/ Al(G)/Pentacene/Au(D) with low working voltage and good detecting property was fabricated, in which the channel length was shortened to nanometer-size to reduce the control voltage effectively by changing the device configuration from common planar type to vertical type. The preparation and current modulation mechanism of the middle aluminum gate electrode were discussed. By compared with the planar FET-based pentacene photodetector ITO(G)/PMMA/Pentacene/Au(S,D) in the full visible region, the vertical configuration device had shown better detecting performance at lower source-drain voltage VDS =-2 V, which was just controlled in a low gate voltage range(VGS =-1 V~1 V).(3) Size uniformed and well solution-dispersed PbS quantum dots(QDs) were synthesized by hot injection method, which were used as absorbing sources of the infrared illumination due to its absorption peak in the near-infrared spectral region. Poly(3-hexylthiophene)(P3HT) was easy to forming film and had good electrical property. The P3 HT and PbS QDs were blended together with the weight ratio of 2:1, 1:1 and 1:2 in chlorobenzene, and the mixed solutions were spin-coated to form different P3HT:PbS quantum dots nanocomposite films as the active layers in the top-gate bottom-contact type FET-based infrared photodetectors Au(S,D)/P3HT:PbS/PMMA/Al(G). In dark and under 980 nm illumination with different intensities, the electrical and detecting parameters of the above three devices were compared with each other. The relationship between the device performance under different incident intensities and the PbS quantum dots percentage in the nanocomposite films were investigated, and the carriers transmission mechanism of the device was analyzed. For the weight ratio of P3 HT to PbS quantum dots of 1:1, the FETbased nanocomposite film infrared photodetector Au(S,D)/P3HT:PbS/PMMA/Al(G) had shown both relatively high electrical and detecting performances.