Extensive reports have demonstrated that one dimensional (1D) nanomaterials, including nanowires (NWs), nanopillars, nanotubes, are superior building blocks for high performance photodetectors due to their unique physical and chemical properties. In this thesis, we have firstly demonstrated polycrystalline ZnO granular nanowire (GNW)-based photodetectors fabricated by an all-printable process. This process is scalable, cost-effective and compatible to rigid and flexible substrates. 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, i,e., the Schottky-like energy barriers in series along the GNW axial di...[ Read more ]

Extensive reports have demonstrated that one dimensional (1D) nanomaterials, including nanowires (NWs), nanopillars, nanotubes, are superior building blocks for high performance photodetectors due to their unique physical and chemical properties. In this thesis, we have firstly demonstrated polycrystalline ZnO granular nanowire (GNW)-based photodetectors fabricated by an all-printable process. This process is scalable, cost-effective and compatible to rigid and flexible substrates. 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, i,e., the Schottky-like energy barriers in series along the GNW axial direction. These barriers lead to highly suppressed dark current of the device, and also give rise to a fast photoelectric response to low intensity optical signal due to the barrier height modulation.

Although NWs can bring in so many advantages to photodetectors, there is still a bottleneck problem holding their wide application: the lack of an effective way to assemble and integrate nanowires into large-scale arrays. Single or multiple NWs based-device usually show poor device stability and reliability. Moreover, they usually have small output. This may finally result in increased cost. In this thesis, we have also developed a unique chemical vapor deposition (CVD) process to grow self-integrated, high density, ordered three-dimensional (3-D) NW arrays in nanoengineering templates. As the nanochannels have largely controllable geometrical factors, namely, periodicity, diameter and depth, NW geometry can also be precisely nanoengineered. Typically, the ordered 3-D NW arrays can achieve high density in the range of 10⁸/cm²~10⁹/cm² with individual NW diameter of 250 nm ~ 130 nm at a sizable scale of ~9 cm². The 3-D NW arrays are conspicuously promising for 3-D integrated nano-electronics/optoelectronics and the difficulty in large-scale NW assembly and integration is avoided. In addition to NWs with uniform diameter, complex structures, such as nanotowers with dual diameters, nanotowers with triple diameters, nanocones, etc, can be obtained by engineering the templates. A variety of materials including inorganic (CdS, ZnO, Ge, Si) and orthometallic semiconductors (CH₃NH₃PbI₃, CH₃NH₃SnI₃, etc) were grown by this method.

To further demonstrate the potency of the NW arrays, CdS and CH₃NH₃PbI₃ 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, thus a simple video was also captured. As the diameter of each NWs can be as small as hundreds of nanometers and each NWs can serve as one pixel, this unique image sensor design can potentially lead to extremely high resolution which is comparable to optical wavelength, if proper top and bottom electrode fabrication technique can be identified. 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 using perovskite NWs. And the 3-D NW image sensor demonstrated here can inspire unconventional design of high resolution and high performance imaging devices.