Examination Committee

Prof Shengwang DU, PHYS/HKUST (Chairperson)
Prof Zhiyong FAN, ECE/HKUST (Thesis Supervisor)
Prof Hyunhyub KO, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (External Examiner)
Prof Levent YOBAS, ECE/HKUST
Prof Kevin J CHEN, ECE/HKUST
Prof Shihe YANG, CHEM/HKUST

Abstract

One dimensional (1D) nanomaterials are superior building blocks of high performance photodetectors due to their unique physical and chemical properties. In this thesis, we have firstly demonstrated polycrystalline ZnO Granual nanowire (GNW)-based photodetectors fabricated by an all-printable process. Systematic characterization revealed their excellent performance, including high photoconductive gain, responsivity and detectivity. Further analysis shows that their high performance originates from their unique band structure.

We have also developed a unique chemical vapor deposition (CVD) process to grow three-dimensional (3-D) NW arrays in nanoengineering templates. The grown ordered 3-D NW arrays are vertically aligned to the substrate and can achieve high density in the range of 108/cm2~109/cm2. Importantly, the NWs growth and integration were achieved at the same time, therefore, the bottleneck challenge in large-scale NW assembly and integration is addressed. The 3-D NW arrays are conspicuously promising for 3-D integrated nano-electronics/optoelectronics. To demonstrate the potency, inorganic and organic-inorganic hybrid NWs have been fabricated into proof-of-concept image sensors. Each image sensor consists of 1,024 photodiode pixels made of vertical NWs, and the imaging function has been verified by recognizing various optical patterns projected on the sensor. It was found that the NW sensors can respond to dynamic optical input with reasonable speed. As the diameter of each NWs can be very small and each NW can serve as one pixel, this unique image sensor design can potentially lead to extremely high resolution.

Overall, the developed novel NW growth process here implements NW growth and integration at the same time and it is likely to be applicable to other materials NW growth, thus can enable a wide range of studies on fundamental properties and device applications. And the 3-D NW image sensor demonstrated here can inspire unconventional design of high resolution and high performance imaging devices.