Characterization of Nano-electric Structure of Materials by Weak Excitation Cathodoluminescence

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We were intended to develop the characterizing technique of electronic structure of nano-scale materials and have fabricated a cathodoluminescence (CL) system which has a spatial resolution of 50 nm. Such a high resolution was realized using low electron beam voltages as 1 kV.A new thermal-field-emission gun was developed to achieve an electron beam current of 5 nA at 1 kV operation. A light collection system with high efficiency was developed using ellipsoidal mirror and fiber optics to detect faint light from nano-materials. Serial (photon counter) and parallel (CCD) light detection systems were also equipped to realize CL image and spectra. CL images were recorded on the memory of computer, which makes it possible to the analyze CL intensity quantitatively. With this system, we have studied quantum structure such as quantum dots and wires.CL from InGaAs/GaAs quantum dot structures formed on the tetrahedral-shaped recesses on GaAs (111)B substrates were extensively studied with analyzing the dependencies of excitation power and observing temperature. The self-organized quantum structure in II-VI semiconductors using Stranski-Krastanov growth were also evaluated with CL.The optical properties of ZnO nano-particles of various shapes, such as hexagonal plates, prisms and tetrapods, were also studied in detail.