Study On The Distribution And Electrical Properties Of GeSi Single Quantum Ring And Single Quantum Dots

Low dimensional self-assembled semiconductor quantum structures such as quantum dots (QDs) and quantum rings (QRs) have received great interests in recent years for their potential applications in optoelectronic devices and quantum computers. In recent decades, scanning probe microscopy (SPM) related techniques have been applied to study the electrical properties of individual quantum structures, which can offer non-averaged quantum properties. In this paper, the composition distributions and electrical properties of individual self-assembled GeSi QRs were studied by SPM, and the relation between the composition distributions of GeSi QDs and the growth temperatures wasalso studied.Firstly, the composition distributions of specific individual QRs were obtained by using selective chemical etching combined with in-situ atomic force microscopy (AFM) imaging. By considering the etched-height of wetting layer and the in-situ analysis of many the same QRs, we get a more accurate composition distribution of GeSiQRs. Meanwhile the conductive properties of individual QRs with different surface composition distributions were investigated by conductive atomic force microscopy (CAFM). It is found that the current distributions are all ring-like for all the QRs that have different composition distributions. So we give a new conductive mechanism for QRs that its current distributions are closely related to its topographic shapes while slightly determined by its composition distributions.Secondly, the surface potential distributions and carrier density distributions of individual QRs with different surface composition distributions were investigated by scanning Kelvin probe microscopy (SKM) and scanning capacitance microscopy (SCM) respectively. The SKM results show that the work function of the QRs’ rim is larger than that of other parts, so the Schottky barrier height at the interface of the tip and rim is lower than that of other parts which is in consistence with the CAFM results. Meanwhile the results of SCM experiment give an additional proof for the CAFM results that the carrier density is richer at the rim of QRs. Combing the results of CAFM, SKM and SCM of BPA-etched QRs (Ge<5%) the influences of the QRs’ microstructures on the electric properties are clarified.Additionally, the composition distributions of two kinds of QDs that were grown at640℃and680℃respectively were obtained by in-situ AFM and selective wet chemical etching. It is found that the composition distributions are symmetry for the QDs that grown at640℃. But for the QDs that grown at680℃the composition distributions are symmetry for the pyramidal QDs while asymmetry for the dome-shaped QDs.Lastly, we make a conclusion for this paper and give some suggestions for the following researches.