QUANTUM DOTS

摘要

A quantum dot (QD) may be defined as a small patch of material confined in all three dimensions to nanometer lengths. When matter is structured and confined on the nanometer scale, some physics of little consequence for bulk systems may dominate important properties of the nanosystems. Interesting new properties of QDs are being exploited to fabricate devices like single-electron transistors, single-photon detectors, lasers, quantum computers, new catalysts and for applications in cryptography, tracing specific proteins within cells etc. QDs can be fabricated by lithography or by self-assembly. The advantages of self-assembled QDs over those lithographically fabricated are explained. Many advanced applications require epitaxially grown QDs on single crystalline substrates. Molecular beam epitaxy (MBE) is the highest precision deposition method used in semiconductor processing. Examples of growth of self-assembled epitaxial QDs by MBE in our laboratory and characterizations of QDs are presented. Single-electron tunneling is an essential aspect of single-electron transistors. Results of single-electron tunneling in QDs showing Coulomb blockade, Coulomb staircase and quantum capacitance are presented. These results were obtained by scanning tunneling spectroscopy (STS) measurements at 103 K in a variable temperature scanning tunneling microscope operating under ultrahigh vacuum and attached to the MBE system. Lastly, an ion-beam replication method for fabricating self-assembled nanostructures is described with examples of Si QDs fabricated on Si.