Quantum Dot Electronic Structure
In an unconfined (bulk) semiconductor, an electron-hole pair is typically bound within a characteristic length, called the exciton Bohr radiaus This is estimated by replacing the positively charged atomic core with the hole in the Bohr formula. If the electron and hole are constrained further, then properties of the semiconductor change. For example, the absorption and emission wavelength of light shifts towards smaller wavelengths. This effect is a form of quantum confinement, and it is a key feature in many emerging electronic structures.
“Besides confinement in all three dimensions i.e. Quantum Dot - other quantum confined semiconductors include:
quantum wires which confine electrons or holes in two spatial dimensions and allow free propagation in the third.
quantum wells which confine electrons or holes in one dimension and allow free propagation in two dimensions.”
Recent Journal Articles
Single-Electron Tunneling through Molecular Quantum Dots in a Metal-Insulator-Semiconductor Structure
(2933–2937)Advanced Functional Materials 21 #15 (2011)
Hayakawa, et al, Japan, demonstrated a single-electron tunneling (SET) in a metal-insulator-semiconductor (MIS) structure in which C60 and copper phthalocyanine (CuPc) molecules are embedded as quantum dots in the insulator layer. The SET is found to originate from resonant tunneling via the energy levels of the embedded molecules, (e.g., the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)). These findings show that the threshold voltages for SET are tunable according to the energy levels of the molecules. Furthermore, SET is observable even near room temperature. The results suggest, together with the fact that these properties are demonstrated in a practical device configuration, that the integration of molecular dots into the Si-MIS structure has considerable potential for achieving novel SET devices. Moreover, the attempt allows large-scale integration of individual molecular functionalities. (RDC 8/9/2011)