How to Visualize the Electronic Structures of Low-dimensional Semiconductors? Using Spatially-Resolved Photoemission Spectroscopy
Jhih-Wei Chen (陳至瑋)1, Chia-Hao Chen (陳家浩)2, Shu-Ju Tsai (蔡淑如)3, Chung-Lin Wu (吳忠霖)1*
1Department of Physics, National Cheng-Kung University, Tainan, Taiwan
2National Synchrotron Radiation Research Center (NSRRC), HsinChu, Taiwan
3Center for Micro/Nano Science and Technology, National Cheng-Kung University, Tainan, Taiwan
* Presenter:Chung-Lin Wu (吳忠霖)
The visualization of the electronic structures of the various compound and low-dimensional semiconductors is the basis for clarifying a variety of property questions and phenomena, and is a prerequisite for the technical applications. In my talk, firstly, using the spatially resolved photoemission spectroscopy (PES) excited by the focused synchrotron radiation (soft x-ray), a direct visualization of the piezoelectricity-induced band structure shift in a single bent ZnO microwire (MW) is presented. Under radial-line scan across the bent section of ZnO MW, the characteristic core-level shifts were directly related to the spatial distribution of piezoelectric potentials perpendicular to the ZnO polar direction. [1] This spectro-microscopic technique allows imaging and identifying the electric-mechanical couplings in the one-dimensional (1D) piezoelectric GaN micro-/nano-wire system. [2] By performing spatially resolved core level spectra of an isolated two-dimensional (2D) WSe2 semiconducting sheet on different polarization domains of supporting ferroelectric substrate, we observe an efficient method to locally confine the electrons/holes in WSe2 and thus create a WSe2 diode defined by a lateral pn homojunction. [3] Moreover, we show that another compound, amorphous silicon nitride (a-Si3N4) grown by plasma-assisted atomic beam deposition (PA-ABD) technique, is a promising candidate effective electrical insulator for use as a high-k dielectric. [4] We demonstrate that charge transport properties in the metal/a-Si3N4/Si (MNS) structures approach defect-free limits with a large breakdown field and a low leakage current. These works might turn out that even if photoemission excited by the synchrotron radiation is different and difficult, it is in any case possible and offers to perform a variety of novel types of investigations on electronic structures of low-dimensional semiconductors.

[1] C.-L. Wang, S.-J. Tsai, J.-W. Chen, H.-W. Shiu, L.-Y. Chang, K.-H. Lin, H.-C. Hsu, Y.-C. Chen, C.-H. Chen, and C.-L. Wu*, “Imaging and Characterization of Piezoelectric Potential in a Single Bent ZnO Microwire”, Appl. Phys. Lett. 105, 123115 (2014)
[2] S.-J. Tsai*, C.-Y. Lin, C.-L. Wang, J.-W. Chen, C.-H. Chen, C.-L. Wu*, “Efficient coupling of lateral force in GaN nanorod piezoelectric nanogenerators by vertically integrated pyramided Si substrate”, Nano Energy 37, 260 (2017)
[3] J.-W. Chen, S.-T. Lo, S.-C. Ho, X.-Q. Zhang, Y.-D. Liu, Y.-Y. Chiou, Y.-X. Chen, J.-C. Yang, Y.-C. Chen, T.-M. Chen, Y.-H. Chu, Y.-H. Lee, C.-H. Chen*, and C.-L. Wu*, “Gate-free Monolayer WSe2 p-n Diode”, to be submitted
[4] S.-J. Tsai*, C.-L. Wang, H.-C. Lee, C.-Y. Lin, J.-W. Chen, H.-W. Shiu, L.-Y. Chang, H.-T. Hsueh, H.-Y. Chen, J.-Y. Tsai, Y.-H. Lu, T.-C. Chang, L.-W. Tu, H. Teng, Y.-C. Chen, C.-H. Chen, and C.-L. Wu*, “Approaching Defect-free Amorphous Silicon Nitride by Plasma-assisted Atomic Beam Deposition for High Performance Gate Dielectric”, Scientific Reports 6, 28326 (2016)

Keywords: Photoemission Spectroscopy, Low-dimensional Semiconductors