量子點具有獨特光學性質和電學特性，舉例來說，量子點照光後能吸收特定能量，使價帶電子躍遷至導帶，並從導帶釋放能量回到基態，產生螢光現象;在電學方面，量子點能把光訊號轉成電訊號，已廣泛應用於太陽能電池和光感測器等元件。
傳統的光感測器大多僅能偵測固定波段的入射光，本論文藉由混合不同量子點有效提高光感測器的偵測範圍。實驗配製單一量子點CdZnS/ZnS、CsPbBr3、InP/ZnSeS 溶液以及混合量子點溶液 (CdZnS/ZnS+CsPbBr3 、 CsPbBr3+InP/ZnSeS 、CdZnS/ZnS+ InP/ZnSeS、CdZnS/ZnS+CsPbBr3+InP/ZnSeS QDs)，並將三種單一和混合量子點滴塗1到5層在矽基板上再沉積銀電極，形成量子點/矽異質接面光感測器。為了分析光測器在寬頻光源下的表現，實驗以白光光源照射三種單一和混合量子點光感測器，量測光感測器的電壓電流、光暗電流比、靈敏度和探測率來分析光感測器的特性。實驗結果顯示混合量子點比單一量子點光感測器具有更寬的頻譜響應，並產生更大光電流與光響應。此外，本論文透過不同層數的量子點最佳化元件特性，其中五層的CsPbBr3+ InP/ZnSeS QDs量子點/矽光感測器之光暗電流比可到達103 倍，顯示光感測器具有優異的偵測特性，未來將非常有潛力應用於寬頻光學偵測系統。

Quantum dots have unique optical and electrical properties, for example, quantum dots can absorb specific energy under light illumination and then electrons will transition from the valence band to the conduction band. The energy is therefore released from the conduction band back to the ground state, generating fluorescence. Additionally, quantum dots can convert optical signals into electrical signals, greatly expanding the scope of applications.In this study, quantum dot solutions including CdZnS/ZnS, CsPbBr3, InP/ZnSeS and mixed solutions (CdZnS/ZnS+CsPbBr3 , CsPbBr3+InP/ZnSeS , CdZnS/ZnS+InP/ZnSeS, CdZnS/ZnS+CsPbBr3+ InP/ ZnSeS QDs are coated 1~5 layers on silicon substrates followed by depositing silver on quantum dots/silicon to construct the contacts. The current-voltage curves, on/off ratios, responsivities, and detectivities of these photodetectors are characterized under a white light illumination. Based on the measured results, the photodetector fabricated with mixed quantum dots displays a better response and has the ability to detect a signal in a wider wavelength range. We further optimize the performance of photodetectors through constructing different layers of quantum dots on Si substrates. The photodetector of five-layered quantum dots containing CsPbBr3 and InP/ZnSeS shows the highest on/off ratio of 103. This mixed quantum dots photodetector enables an improved absorption wavelength range,resulting in higher performance that can potentially open up a new pathway for optoelectronic systems in the future.

[1] Singh, V. K., M. Yadav, S., Mishra, H., Kumar, R., Tiwari, R. S., Pandey, A., & Srivastava, A. (2019). WS2 quantum dot graphene nanocomposite film for UV photodetection. ACS Applied Nano Materials, 2(6), 3934-3942.
[2] Lee, K. H., Han, C. Y., Kang, H. D., Ko, H., Lee, C., Lee, J., ... & Yang, H. (2015). Highly efficient, color-reproducible full-color electroluminescent devices based on red/green/blue quantum dot-mixed multilayer. ACS nano, 9(11), 10941-10949.
[3] Alivisatos, A. P. (1996). Semiconductor clusters, nanocrystals, and quantum dots. science, 271(5251), 933-937.
[4] Fang, T., Wang, T., Li, X., Dong, Y., Bai, S., & Song, J. (2021). Perovskite QLED with an external quantum efficiency of over 21% by modulating electronic transport. Science Bulletin, 66(1), 36-43.
[5] Mostafa, M., El Nady, J., Ebrahim, S. M., & Elshaer, A. M. (2021). Synthesis, structural, and optical properties of Mn2+ doped ZnS quantum dots for biosensor application. Optical Materials, 112, 110732.
[6] Bera, D., Qian, L., Tseng, T. K., & Holloway, P. H. (2010). Quantum dots and their multimodal applications: a review. Materials, 3(4), 2260-2345.
[7] De, C. K., Routh, T., Roy, D., Mandal, S., & Mandal, P. K. (2018). Highly photoluminescent InP based core alloy shell QDs from air-stable precursors: excitation wavelength dependent photoluminescence quantum yield, photoluminescence decay dynamics, and single particle blinking dynamics. The Journal of Physical Chemistry C, 122(1), 964-973.
[8] Wei, Y., Cheng, Z., & Lin, J. (2019). An overview on enhancing the stability
of lead halide perovskite quantum dots and their applications in phosphor-converted LEDs. Chemical Society Reviews, 48(1), 310-350.
[9] Ji, Z., Dervishi, E., Doorn, S. K., & Sykora, M. (2019). Size-dependent el-
ectronic properties of uniform ensembles of strongly confined graphene quantum dots. The journal of physical chemistry letters, 10(5), 953-959.
[10] Dervishi, E., Ji, Z., Htoon, H., Sykora, M., & Doorn, S. K. (2019). Raman spectroscopy of bottom-up synthesized graphene quantum dots: size and structure dependence. Nanoscale, 11(35), 16571-16581.
[11] Shen, X., Zhang, Y., Kershaw, S. V., Li, T., Wang, C., Zhang, X., ... & Rogach, A. L. (2019). Zn-alloyed CsPbI3 nanocrystals for highly efficient perovskite light-emitting devices. Nano letters, 19(3), 1552-1559.
[12] Kim, Y., Ham, S., Jang, H., Min, J. H., Chung, H., Lee, J., ... & Jang, E. (2019). Bright and uniform green light emitting InP/ZnSe/ZnS quantum dots for wide color gamut displays. ACS Applied Nano Materials, 2(3), 1496-1504.
[13] Boles, M. A., Ling, D., Hyeon, T., & Talapin, D. V. (2016). The surface science of nanocrystals. Nature materials, 15(2), 141-153.
[14] Smith, A. M., & Nie, S. (2010). Semiconductor nanocrystals: structure, properties, and band gap engineering. Accounts of chemical research, 43(2), 190-200.
[15] Choudhury, B., Dey, M., & Choudhury, A. (2014). Shallow and deep trap emission and luminescence quenching of TiO 2 nanoparticles on Cu doping. Applied Nanoscience, 4(4), 499-506.
[16] Richter, A., Glunz, S. W., Werner, F., Schmidt, J., & Cuevas, A. (2012). Improved quantitative description of Auger recombination in crystalline silicon. Physical review B, 86(16), 165202.
[17] Zhang, L., Yin, L., Wang, C., Lun, N., Qi, Y., & Xiang, D. (2010). Origin of visible photoluminescence of ZnO quantum dots: defect-dependent and size-
dependent. The Journal of Physical Chemistry C, 114(21), 9651-9658.
[18] Ding, H. L., Zhang, Y. X., Wang, S., Xu, J. M., Xu, S. C., & Li, G. H. (2012). Fe3O4@ SiO2 core/shell nanoparticles: the silica coating regulations with a single core for different core sizes and shell thicknesses. Chemistry of Materials, 24(23), 4572-4580.
[19] Imran, M., Caligiuri, V., Wang, M., Goldoni, L., Prato, M., Krahne, R., ... & Manna, L. (2018). Benzoyl halides as alternative precursors for the colloidal synthesis of lead-based halide perovskite nanocrystals. Journal of the American Chemical Society, 140(7), 2656-2664.
[20] Chang, S., Bai, Z., & Zhong, H. (2018). In situ fabricated perovskite nanocrystals: a revolution in optical materials. Advanced Optical Materials, 6(18), 1800380.
[21] Regulacio, M. D., & Han, M. Y. (2010). Composition-tunable alloyed semiconductor nanocrystals. Accounts of chemical research, 43(5), 621-630.
[22] Xu, X., Gabor, N. M., Alden, J. S., Van Der Zande, A. M., & McEuen, P. L. (2010). Photo-thermoelectric effect at a graphene interface junction. Nano letters, 10(2), 562-566.
[23] Zhang, Q., Jie, J., Diao, S., Shao, Z., Zhang, Q., Wang, L., ... & Lee, S. T. (2015). Solution-processed graphene quantum dot deep-UV photodetectors. ACS nano, 9(2), 1561-1570.
[24] Dong, Y., Gu, Y., Zou, Y., Song, J., Xu, L., Li, J., ... & Zeng, H. (2016). Improving all‐inorganic perovskite photodetectors by preferred orientation and plasmonic effect. Small, 12(40), 5622-5632.
[25] Kwak, D. H., Ramasamy, P., Lee, Y. S., Jeong, M. H., & Lee, J. S. (2019). High-performance hybrid InP QDs/black phosphorus photodetector. ACS
applied materials & interfaces, 11(32), 29041-29046.
[26] Kumar, Y., Kumar, H., Rawat, G., Kumar, C., Pal, B. N., & Jit, S. (2018). Spectrum selectivity and responsivity of ZnO nanoparticles coated Ag/ZnO QDs/Ag UV photodetectors. IEEE Photonics Technology Letters, 30(12), 1147-1150.
[27] Sarto, A. W., & Van Zeghbroeck, B. J. (1997). Photocurrents in a metal-semiconductor-metal photodetector. IEEE journal of quantum electronics, 33(12), 2188-2194.
[28] Izadpour, A. R., Jahromi, H. D., & Sheikhi, M. H. (2018). Plasmonic enhancement of colloidal quantum dot infrared photodetector photosensitivity. IEEE Journal of Quantum Electronics, 54(3), 1-7.
[29] Wang, X., Yu, J., & Chen, R. (2018). Optical characteristics of ZnS passivated CdSe/CdS quantum dots for high photostability and lasing. Scientific reports, 8(1), 1-7.
[30] Li, X., Wu, Y., Zhang, S., Cai, B., Gu, Y., Song, J., & Zeng, H. (2016). CsPbX3 quantum dots for lighting and displays: room‐temperature synthesis, photoluminescence superiorities, underlying origins and white light‐emitting diodes. Advanced Functional Materials, 26(15), 2435-2445.
[31] Jang, E., Kim, Y., Won, Y. H., Jang, H., & Choi, S. M. (2020). Environmentally friendly InP-based quantum dots for efficient wide color gamut displays. ACS Energy Letters, 5(4), 1316-1327.
[32] De Iacovo, A., Venettacci, C., Giansante, C., & Colace, L. (2020). Narrowband colloidal quantum dot photodetectors for wavelength measurement applications. Nanoscale, 12(18), 10044-10050.
[33] Sun, Z., Liu, Z., Li, J., Tai, G. A., Lau, S. P., & Yan, F. (2012). Infrared
photodetectors based on CVD‐grown graphene and PbS quantum dots with
ultrahigh responsivity. Advanced materials, 24(43), 5878-5883.
[34] Li, J., Xia, J., Liu, Y., Zhang, S., Teng, C., Zhang, X., ... & Wei, G. (2020). Ultrasensitive Organic‐Modulated CsPbBr3 Quantum Dot Photodetectors via Fast Interfacial Charge Transfer. Advanced Materials Interfaces, 7(2), 1901741.
[35] Wei, T. Y., Huang, C. T., Hansen, B. J., Lin, Y. F., Chen, L. J., Lu, S. Y., & Wang, Z. L. (2010). Large enhancement in photon detection sensitivity via Schottky-gated CdS nanowire nanosensors. Applied Physics Letters, 96(1), 013508.
[36] Li, H., Wang, X., Xu, J., Zhang, Q., Bando, Y., Golberg, D., ... & Zhai, T. (2013). One‐dimensional CdS nanostructures: a promising candidate for optoelectronics. Advanced Materials, 25(22), 3017-3037.
[37] Khan, A. A., Yu, Z., Khan, U., & Dong, L. (2018). Solution processed trilayer structure for high-performance perovskite photodetector. Nanoscale research letters, 13(1), 1-10.
[38] Tang, X., Han, S., Zu, Z., Hu, W., Zhou, D., Du, J., ... & Zang, Z. (2018). All-Inorganic perovskite CsPb2Br5 microsheets for photodetector application. Frontiers in Physics, 5, 69.
[39] Kufer, D., Nikitskiy, I., Lasanta, T., Navickaite, G., Koppens, F. H., & Konstantatos, G. (2015). Hybrid 2D–0D MoS2–PbS quantum dot photodetectors. Advanced materials, 27(1), 176-180.