Topographic analyzer for electronic structures of semiconductors

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In this project, a novel analyzer has been developed to obtain an image of photoluminescence (PL), optical properties, or optoelectronic properties with a spatial resolution close to the diffraction limit at a low temperature. The analyzer consists of an objective with a high magnification, a novel developed thermal isolation, and an anti-vibration mechamism. A sample is scanned with piezo actuators to obtain the signal image. The sample is cooled down by a cold head with liquid He. A clear reflectance image of SiO_2/Si with a microstructure was obtained at 15 K with a spatial resolution of 0.8 mum. The spatial resolution closes to the theoretical limit determined with the wavelength of the light (632nm) and the numerical aperture of the objective (NA=0.09).GaAs_<1-x>P_x (0.2<x<0.7) was grown on a Si substrate with a GaP buffer layr by metalorganic molecular beam epitaxy. The epilayr showed a spatial fluctuation of composition x. Using spatially reesolved PL,the dependence of PL emitted from GAAs_<1-x>P_x on composition x was precisely characterized. Peaks observed in PL of GaAs_<1-x>P_x was attributed to donor-acceptor pairs related to vacancies in epilayrs based on the results of the spatially resolved PL.The topographic analyzer enables to investigate electronic structures of micro- and nano-structure of semiconductors with a higher sensitivity than that of an optical probe microscope. The topographic analyzer will open a new approach to study semiconductor materials and devices.