Atomically resolved carrier transport behavior under light illumination at heterointerfaces

• Main Authors: Fei-Mam Hsiao, 蕭斐蔓
• Other Authors: Shiow-Fon Tsay
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/xu4e59

博士 === 國立中山大學 === 物理學系研究所 === 106 === The behavior of carrier transport under light illumination at heterointerfaces is an important factor in realizing the basic properties of optoelectronic devices or photocatalytic reaction. In this thesis, light-modulated cross-sectional scanning tunneling microscopy (LM-XSTM) and spectroscopy (XSTS) is utilized to obtain the electronic structures and the change of band alignment at the heterointerface illuminated by a laser. The quality on the growth of heterostructures strongly depends on the lattice mismatch of heterostructures. Therefore, the motivation of my research is to study the behavior of laser-excited carrier at different heterostructures. My work can separate into two systems of heterostructures: The first system is a heterointerface between GaN films and silicon (111) substrate. The heterointerface consists of nanoscale wurtzite and zincblende crystallites with varying crystal orientations and hence contain high defect state densities. We probe an obvious increase in the tunneling current during sub-bandgap laser illumination for the GaN layer with high defect density. With the help of a quantitative model to calculate light-excited tunneling, the route for laser-excited carriers generated at silicon across the interface of GaN/Si is excluded. The result of simulation confirms that the laser-excited carriers only generated at the GaN layers are the excitation of free charge carriers at defect states. The second part is a heterostructure of two-dimensional exfoliated Ca2Nb3O10 (CNO) perovskite nanosheets fabricated on Pt(100) substrate. A Moiré pattern resulting from the interlayer van der Waals interaction is weak to form a lattice-matched coherent heterostructure is observed. Additionally, the band alignments across the heterostructures due to the stacking effect with and without light are illustrated. The technique of using light-modulated cross-sectional scanning tunneling microscopy is unique to study the behavior of light-excited carriers at heterointerfaces. The fundamental study across the heterointerfaces potentially provides the crucial information for improving the knowledge of fundamental physical properties and the performance of devices at heterostructures.