Browsing by Author "Hsieh, PC"

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Effect of growth rate on the composition fluctuation of InGaAsN/GaAs single quantum wells
(2006-06-15)
Chen, JF
;
Hsiao, RS
;
Hsieh, PC
;
Wang, JS
;
Chi, JY
Effect of growth rate on the composition fluctuation is investigated in In0.34Ga0.66As0.98N0.02/GaAs single quantum wells (QWs) by photoluminescence (PL), transmission electron microscopy, and admittance spectroscopy. In an InGaAsN layer grown at a normal growth rate, the PL spectra show a low-energy bump at the tail of an InGaAsN emission, suggesting the presence of composition fluctuation. Lowering the growth rate degrades the composition fluctuation by segregating into bimodal phases of an InGaAsN and InGaAs-rich phase. Further lowering the growth rate leads to a three-dimensional growth and enhances the InGaAs-rich phase. The carrier distribution for the InGaAsN layer grown at the normal rate shows a carrier bump at the tail of a strong accumulation peak, suggesting the presence of an electron state below the QW ground state. The admittance spectroscopy shows that the activation energy (32 meV) of this electron state is comparable to the energy separation (30 meV) between the InGaAsN emission and the low-energy bump, and thus it is possible that the composition fluctuation actually induces an electron state closely below the QW ground state. (c) 2006 American Institute of Physics.
N incorporation into InGaAs cap layer in InAs self-assembled quantum dots
(2005-12-01)
Chen, JF
;
Hsiao, RS
;
Hsieh, PC
;
Chen, YJ
;
Chen, YP
This study presents the results of incorporating N into self-assembled InAs quantum dots (QDs) capped with an InGaAs cap layer. Experimental results indicate that such incorporation can redshift the QD ground state and decrease the energy spacing between the QD ground and first excited states. However, this incorporation reduces the potential barrier of the cap layer, increasing the electron escape from the QDs. Capacitance-voltage profiling shows that a broad shoulder corresponding to the electron emission from the QD ground to first-excited state cannot be resolved from the peak related to the electron emission from the excited states upon this incorporation. This finding implies that this incorporation reduces the energy spacing between the QD ground and first-excited states in the conduction band, thus correlating well with the photoluminescence data. In contrast, incorporating N directly into the InAs QD produces no redshift of the emission wavelength but introduces a deep trap at similar to 0.21 eV that depletes the electrons in the QDs. (c) 2005 American Institute of Physics.