Title:Quantum impurity state and local electronic properties of semiconductor nanostructure

Speaker: Prof. Zhaozhong Wang

Time：Aug 28，2009  10:00（AM）

Venue：Institute of Semiconductors,  CAS

Abstract：Doping a semiconductor with foreign atoms allows to precisely control the concentration of charge carriers, a principle at the basis of virtually all electronic and optoelectronic devices. In quantum mechanics, an impurity inside a semi-conductor can be assimilated as a hydrogen atom. Binding energy and the Bohr radius of a single impurity are two essential parameters in this simple approximation. It has been highly desirable to measure the Bohr radius directly since last three decades.We use scanning tunneling microscopy and spectroscopy to study donor-like point defects which are located at the epitaxial surface of a quantum well (QW). Special designed InGaAs surface QWs are grown by molecular beam epitaxy (MBE) for this study. Four different QWs with thickness of 2, 6, 10 and 14 nm are investigated. By measuring the local density of the state in the QW with nanometer scale resolution, we are able to determine both the binding energy and the Bohr radius of single defects. In a QW of 14nm thickness, the binding energy of a single point defect is found to be 10 meV and its Bohr radius deduced is of 12nm. More, we find that the binding energy and the Bohr radius highly depend on the thickness of QW. The important increase of binding energy in semiconductor nanostructure might prohibit the impurity ionization process at room temperature for p-type doping. Our results are in quantitative agreement with the hydrogenic model. (PRL 100, 056806, 2008).In this talk, our investigation of the local electronic properties of semiconductor and their application in device are presented too.