Browsing by Author "Lin, H."

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Anomalous diamagnetic shift for negative trions in single semiconductor quantum dots
(2010-03-01)
Fu, Y. J.
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Lin, S. D.
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Tsai, M. F.
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Lin, H.
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Lin, C. H.
We report on the magnetic response of negative trions X(-) in single self-assembled InAs/GaAs quantum dots. Unlike the conventional quadratic diamagnetic shift for neutral excitons, the observed X(-) diamagnetic shifts are small and nonquadratic. In particular, we also observed a reversal in sign of the conventional diamagnetic shift. A theoretical analysis indicates that such anomalous behaviors for X(-) arise from an apparent change in the electron wave function extent after photon emission due to the strong Coulomb attraction induced by the hole in its initial state. This effect can be very pronounced in small quantum dots, where the electron wave function becomes weakly confined and extended much into the barrier region. When the electrons gradually lose confinement, the magnetic response of X(-) will transit gradually from the usual quadratic diamagnetic shift to a quartic dependence, and finally into a special paramagnetic regime with an overall negative energy shift.
Carrier gas effects on the SiGe quantum dots formation
(2008-07-30)
Lee, C. -H.
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Yu, C. -Y.
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Lin, C. M.
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Liu, C. W.
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Lin, H.
SiGe quantum dots (QDs) grown by ultra-high vacuum chemical vapor deposition using H(2) and He carrier gases are investigated and compared. SiGe QDs using He carrier gas have smaller dot size with a better uniformity in terms of dot height and dot base as compared to the H(2) carrier gas. There is a higher Ge composition and less compressive strain in the SiGe QDs grown in He than in H(2) as measured by Raman spectroscopy. The Ge content is higher for He growth than H(2) growth due to hydrogen induced Si segregation and the lower interdiffusivity caused by the more strain relaxation in the He-grown SiGe dots. The photoluminescence also confirms more compressive strain for H(2) growth than He growth. Hydrogen passivation and Ge-H cluster formation play an important role in the QDs growth. (C) 2008 Elsevier B. V. All rights reserved.