PbS COLLOIDAL QUANTUM DOTS BASED PHOTODETECTORS FOR INTEGRATED SWIR DETECTION
Electronics Engineering, Ph.D. Dissertation, 2012
Prof. Dr. Yaşar Gürbüz, Asst. Prof. Cem Öztürk, Prof. Dr. Yusuf Menceloğlu, Asst. Prof. Volkan Özgüz, Assoc. Prof. Şenol Mutlu
Date & Time: August 6th 2012 – 14:30
Place: FENS L047
Keywords: Colloidal quantum dots, solution processed phododiodes, PbS colloidal quantum dots, SWIR detection, photodiodes, photoconductors, ITO sputter deposition, fully integrated FPAs
Due to the low water absorption and nightglow, sensing in SWIR is very attractive in applications such as; passive night vision, biomedical imaging and remote sensing. The fully integration of photodetectors to the read-out circuits is desirable in many applications in order to increase density of detectors, reduce costs, system size and power consumption. Solution-processed semiconductors are a promising alternative to conventional bulk crystalline photodetectors since their production is low cost and easy, their bandgap can be tuned depending on their sizes, and they can be easily integrated on any substrate. In this work, PbS colloidal quantum dot based photodiodes are realized that are compatible with the integration on read out electronics.
PbS quantum dots with the size of 5.3 nm is used that have absorption peaks around 1450 nm. Various kinds of PbS quantum dots based schottky diodes are designed on glass and silicon substrates. Spin deposition steps and solid state ligand exchange processes are optimized to create pinhole free and high mobility PbS quantum dot layers. Lifetime drawback of PbS CQD are studied and improved by ligand exchange and process optimization. In addition to that IC integrable versions of PbS CQD photodiodes are realized. ROIC chip surface is mimicked on Si substrates and fabrication steps are optimized for integration. Special importance is given to optimize highly conductive and transparent indium tin oxide layer using DC magnetron sputtering. Sensitivities close to the conventionally used crystalline, bulk photodetectors is achieved. Also, plasmonic effects of metal nanoparticles in PbS CQD layer are studied. Absorption and photocurrent enhancement is presented using gold nanoparticles in PbS CQD based photoconductors.