1. Self-Assembled Quantum Dot Molecules Studied by AFM
Fengfeng Ye, Yifei Zhang, Yi Lv, Shihua Zhang, Zuimin Jiang and Xinju Yang
Phys. Dept., Fudan Univ., Shanghai, People’s Republic of China
I. Introduction
Because of the three-dimensional confinement of charge carriers, quantum dots are also referred to as ‘artificial atoms’. It is clear that new functionalities can be expected for interacting QD systems, forming artificial molecules or even solids and crystals. Semiconductor quantum dot molecules (QDMs) are systems composed of two or more closely spaced and interacting QDs. Now we studied vertical and lateral coupling Ge/Si quantum dots by expended atomic force microscopy (AFM) to explore new phenomena, such as resonant tunneling, energy shifts of the band-gap and so on.
II. Result of Conductive Atomic Force Microscopy (C-AFM)
An I-V curve which like staircase means a corresponded peak in density of state
Diagram of double layered Ge/Si quantum dots
I-V curve and simultaneously measured density of state
Normal dot density
Single layer
Double layer
High dot density
III. Result of Kelvin Probe Force microscopy (KPFM)
KPFM is a method that directly measure the Fermi level of the sample surface.
I-V curve which like staircase show the electron resonant tunneling of coupled quantum dots
The surface potential can give information about strain, composition, quantum confinement, band gap of quantum dots
IV. Summary
There exists the electron resonant tunneling both in vertical and lateral coupled Ge/Si quantum dots.
We can see the size dependent of surface potential in quantum dots which show that dot size decides the quantum confinement.
KPFM is a method to find out coupling effects of coupled quantum dots.