JAIST Repository: 半導体シングルヘテロ接合における集団的サブバンド間電子励起による共鳴光散乱の理論
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(2) Theory of Resonant Light Scattering by Intersubband Electro Excitations in Semiconductor Single Heterojunctions Soe Myint Maung. (Katayama Lab.). Light scattering spectra by coupled intersubband plasmon-longitudinal optica I have been studied in semiconductor heterostructures such as modulation d excitations -and(I +) quantum-well (MQW) structures and single heterojunctions. In a recent work, the absence + due to the upper branch of the coupled intersubband plasmon-LO phonon modes from quasiGa0.7As/GaAs single heterojunction was reported electron gas (2DEG)δ-doped in Si 0.3 Al + mode [1]. The I peak was also not seen in the earlier data by Pinczuk and Worlock [2] in single heteroj In this thesis we have developed a theory of resonant light scattering by int excitations in semiconductor single heterojunctions. Our theory involves the dynamical of 2DEG taking into account electron-electron and electron-phonon interactions. We con density excitations in 2DEG coupled with LO phonons via the depolarized electric field time Green`s function technique, general expressions for light scattering intensity by obtained. To explore the origins of the absence of the I we have carried out numerical calculation + peak, spectral intensity based on the self-consistent subband energies and →1 wave functions, intersubband transition with energy splitting E 01=E1-E 0. We found that the Coulomb11 plays lengththe L important role to determine the depolarizati from the intersubband transitions, and the dynamical electron-electron Coulomb interac ionic dielectric function is enhanced as the frequency approaches the LO phonon frequen of the11=5, IL 10, 20 Å and damping constants role of 11, Lwe have depicted the intensities - and+ Iassuming and Γph=1 meV in Fig.1.11 As decreases L from 20 to + 5 peak Å, the I for electrons and phonons, τe=2 meV 1/ approaches the LO phonon frequency and the intensity diminishes shifts towhile lowerthe I - peak strongly, frequency side and its intensity increases. Figures 2(a) and (b) show the experimental 2D Our calculated values of 11LE are 19.2 meV and 5.12 Å, assuming 2DEG concentration = N 01 and s 11 -2 peak I weak compared -peak. to that Therefore, of I it 5.3x10cm at T = 9 K. Our calculated + is extremely can be concluded that the absence is the due Ito the smallness of L with11~15 that (L + line of 11 in comparison Å) of MQW [2] so that the strong anti-screening by the ionic dielectric function occu rise to the decrease of scattering intensity by the I + mode.. −. Fig.1: Calculated light scattering intensities Fig.2: Comparis and + lines I for 20 Å ing intensity (a) with calcul of IL 11=5,15,and. References [1] S. Katayama, M. Koyano and S. Yamada, phys. 215, 359 stat. (1999). sol. (b) ，Surf. [2] A. Pinczuk and J.M. Worlock Sci. 113, 69 (1982). Keywords:. resonant light scattering, intersubband excitations, coupled plasmon-phonon.
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