Piezoelectric Photothermal Spectroscopy (PPTS) detection of the nonradiative electron transitions in semiconductors (recent publications)
    Piezoelectric photothermal (PPT) spectroscopy, recently developed from PAS (Photoacoustic Spectroscopy), has been used for investigating physical properties of semiconductors. One of the advantages of this experimental methodology is that it is a direct monitor of the nonradiative recombination processes. Heat generated by the nonradiative recombinations of photoexcited electrons are detected with high sensitivity. Therefore, the PPT technique complements the well-known photoluminescence (PL) technique, which can directly detect the radiative recombination processes. The other advantage is that the PPT spectroscopy is sensitive to a very small optical absorption coefficient in a highly transparent sample. In the pem laboratory, we are investigating the physics of deep levels in semiconductors by using the PPT technique for:
    1. Thin film quantum structure for optoelectronic devices (GaInNAs,GaN, ...)
    2. Chalcopyrite semiconductors for solar cells (CuInSe2, CuGaSe2,....)
    3. Low dimensional bulk semiconductors (layer compounds)
    4. LSI wafer substrate semiconductors (GaAs,Si)

　

Metastable phase and structural dynamics of amorphous semiconductors (recent publications)

    Many variety of materials are included in amorphous semiconductors. The researches of following topics are in progress.

    1. The activation energy of glass transition in chalcogenide glass measured by differential scanning calorimetory (DSC). We treated Ge-Se system added with P,Sb and Bi.
    2. Photo and thermal induced crystallization in a-GeSe2. The crystallization process is measured by time-resolved raman scattering spectroscopy.
    3. Network structure of the glass based on selenium.

　

Physics of intercalated layer semiconductors and its application to the secondary solar batteries (recent publications)
    Layer-type compound semiconductors are known to be a new class of solar cell materials. Large optical to electrical energy conversion efficiencies have been obtained. This layer material, on the other hand, is easily intercalated by alkali metals and molecules. This fact induces a potential application to the Li-intercalated secondary batteries with high energy density. In our pem laboratory, the detail of the electronic and/or electrochemical properties of these semiconductors has been investigated.