Investigation of Optical Absorption Spectra of Extremely Thin Semiconductor Quantum Structure by a Piezoelectric Photothermal Spectroscopy

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Optical absorption spectrum for GaInNAs/GaAs single quantum well structure was obtained precisely by means of our developed Piezoelectric Photothermal Spectroscopy(PPTS) with taking into account a photovoltaic effect. Since the thickness of the sample was extremely thin, usual absorption measurement technique was useless. Detailed analysis of the spectra gave us clear understandings both for two dimensional densities of states of the quantum levels in the conduction and valence bands and exciton formations. Since the present results made possible for precise fitting the line shape of the exciton absorption by a quasi-Voigt function, the binding energies of the exciton were accurately determined as a function of the well thickness and measuring temperature. Theoretical consideration for the binding energy and blue shift of the critical energies of the quantum levels were also carried out. We found that effective mass difference between inside and outside the quantum well and band offset ratio in the conduction band played important roles for generating the PPT spectra. Since the non-radiative intra-band transition determines the temperature dependence of the intensities of the PPT signal, we found the non-radiative transition pathways in the strained quantum well structures. At the same time, we could investigate the oxygen vacancies in the transparent conducting oxidize ZnO and the proton irradiation induced defect in chalcopyrite semiconductor thin films by using the present PPTS methodology. These results in this project make clear that the PPTS technology is a new and effective optical technique for investigating the quantum structure, including the wires and the dots, of the semiconductor devices.