| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 2006: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2005: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
We have theoretically studied the optical polarization in columnar InAs/GaAs quantum dots (QDs), in which the self-assembled QDs are vertically stacked with no interdot spacing. The model structure of the columnar QDs consists of truncated-cone-shaped InAs QDs with the stacking-layer numbers (SLNs) of 1, 3, 5, 7, and 9. We used the valence-force-field model to calculate the strain distribution. We find that the biaxial strain in the middle layers of the columnar QDs decreases with increasing SLN and becomes negative for SLN=9. This is due to the condition that the vertical lattice constant of InAs in these layers has to match that of the side GaAs. By using the strain-dependent 8-band kp theory for the electronic states, we calculated the transverse-electric(TE)- and transverse-magnetic(TM)-mode intensities for the electron-hole transitions. The piezoelectric effect is included in the calculations. For SLN=1 and 3, only the TE-mode transition occurs. With increasing SLN beyond 3, the TM-mode intensity increases while the TE-mode one decreases. Consequently, when SLN changes from 7 to 9, the dominant polarization character changes from the TE mode to the TM mode. This dominant polarization change is attributed to the increase of the light-hole character in the wave function of the ground hole state, which is the consequence of the negative biaxial strain in the middle layers for SLN=9. The change in the optical polarization calculated in this study is in good agreement with the photoluminescence experiment reported by Kita et al., Jpn. J. Appl. Phys., Part 2 41, L1143(2002).
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