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Research Areas

Optical and electrical characterization of semiconducting materials and devices

Piezoelectric Photothermal Spectroscopy
(Surface/Interface) Photovoltaic effect
Photoluminescence
Raman scattering spectra (Microscopic)
Optical absorption and reflectance
Electrical transport measurements
X-ray Duffraction

Our newly developed
Piezoelectric Photothermal Spectroscopy (PPTS)

Advantages of our PPTS methodology

(1)
Electron transitions through defect levels usually involve a non-radiative recombination process due to a strong electron-lattice interaction. The PPTS methodology is only and unique experimental technique to clarify directly such non-radiative transition. This enables us to understand the defect dynamics in semiconductors.

(2)
Since the PPTS technique gives an absolute value for the optical absorption spectrum, sensitivity becomes extremely high for investigating very low concentration of impurity and defect levels. Usual transmission technique gives only a relative value for the absorption spectra. Detailed discussion for the optical absorption will be done for thin films and quantum structures.

(3)
Since the PPTS methodology can eliminate an effect of light diffusive scattering, say, at the interface of the grain boundaries, accurate absorption spectrum are well investigated for the polycrystalline materials.

　Problems of our PPTS methodology

(1)	Theoretical prediction for the signal generation mechnaism is not easy . Complex differentail equations should be solved.
(2)	Other photovoltaic effect such as surface photovoltage should be considered for the carrier diffusion and drift phenomena.

Recent Works

Characterization of the semiconducting properties by using
Piezoelectric Photothermal Spectroscopy (PPTS) and/or
Photovoltaic effect at the interface/surface

Proton irradiated solar cell material CuInSe2	jump
Defect levels in Transparent conductive Oxide ZnO	jump
Quantum Well structure of GaInNAs Thin Films	jump
High rate deposition of microcrystalline Si solar cells	jump
InxGa1-xN Grown by Radio-Frequency Molecular Beam Epitaxy	jump

tram/Strasbourg

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(1)	Electron transitions through defect levels usually involve a non-radiative recombination process due to a strong electron-lattice interaction. The PPTS methodology is only and unique experimental technique to clarify directly such non-radiative transition. This enables us to understand the defect dynamics in semiconductors.
(2)	Since the PPTS technique gives an absolute value for the optical absorption spectrum, sensitivity becomes extremely high for investigating very low concentration of impurity and defect levels. Usual transmission technique gives only a relative value for the absorption spectra. Detailed discussion for the optical absorption will be done for thin films and quantum structures.
(3)	Since the PPTS methodology can eliminate an effect of light diffusive scattering, say, at the interface of the grain boundaries, accurate absorption spectrum are well investigated for the polycrystalline materials.