Basic research of an efficient THz emitting device using an intersubband transition in a quantum dot

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(1) The purpose of this research project is to apply an intersubband transition in a quantum dot, of which transition energy is in a photon energy range of THz electro magnetic radiation, to an efficient light emitting source for THz radiation.(2) Theoretical analysis of quantized levels formed in a quantum dot, which consists of InAs dot grown on GaAs substrate, is carried out by considering the pyramidal shape of the dot and internal strain distribution due to the lattice mismatch between InAs and GaAs. The energy of the levels and the polarization of the transition between the levels has been calculated by three dimensional analysis of the wave function.(3) The examination of the growth method/condition of quantum dot was investigated by considering the THz radiation efficiency. The MBE method has been shown to useful since the distribution in size is comparatively small, as a result of the comparison between the OMVPE and MBE method.(4) Interband transition of the quantum dot, whic … More h is fabricated by the above method, was investigated by using polarization resolved photo luminescence method. By comparing the measured result with the theoretical analysis, we distinguished the energy and symmetry of the quantized levels formed in the dot.(5) We succeeded in the observation of the THz electromagnetic wave associated with the intersubband transition in a quantum dot for the first time, by injecting electron hole pairs into a PIN photodiode, of which insulator layer is consist of quantum dots. The result agreed well with the emission efficiency simulated by Monte-Carlo method.(6) Furthermore, we proposed a cascade injection of electrons into stacked quantum dots for the improvement of THz emission efficiency. Numerical simulations were carried out by considering a carrier relaxation dynamics between quantized levels. It has been shown that the emission efficiency is improved by a factor of 5 compared to the device based on the electron hole pair injection. It has been also shown that a population inversion can be formed in the device based on the cascade injection. Less