Size dependence in charge transport and electronic structure of semiconductor quantum-dot arrays

• Main Authors: Chaung, Wei-Lun, 莊維倫
• Other Authors: Jian, Wen-Bin
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/05592069460498482052

碩士 === 國立交通大學 === 電子物理系所 === 98 === Various diameters (5-20 nm) of PbSe semiconductor quantum dots were synthesized through a colloidal synthesis technique and used for the investigation of quantum confinement, Coulomb blockade, and atomic-like electronic states. In this work, the size dependence of charge transport and electronic structure of PbSe QD arrays were studied. Various sizes of QD self-assembled, two-dimensional islands (clusters or arrays) were deposited on flat gold surface for the scanning tunneling spectroscopy measurement at room temperature, liquid-nitrogen, or liquid-helium temperatures. For data taken at room and liquid-nitrogen temperatures, the double tunneling junction model was used to analyze the current-voltage (I-V) curves of the QD arrays to derive the tip-to-array and the array-to-substrate capacitances. It is found that the array-to-substrate capacitances are not linearly proportional to the size of the QD arrays, so the array cannot be taken as a simple island. We therefore used another analysis method, applying the collective Coulomb blockade theory to exploration of these I-V curves. For data taken at 5 K (liquid-helium temperature), the differential conductance (dI/dV versus V) spectra of the QD arrays reveal atomic-like electronic states. The data were fitted by using the Gaussian function to find multiple quantized electron and hole states. It is observed that the quantized states become broadened and energy gap narrowed down as the number of QD is increased. This result implies that there must be interdot, electrical coupling between the PbSe QDs, resulting in delocalization of quantized electrons and holes in the QD arrays.