Browsing by Author "Tyan, SL"

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An investigation of quantum states in ultra-small InAs/GaAs quantum dots by means of photoluminescence
(2005-08-01)
Wu, CH
;
Lin, YG
;
Tyan, SL
;
Lin, SD
;
Lee, CP
The quantum states of InAs/GaAs quantum dots (QDs) with a base length of less than 10 nm are studied by means of excitation and temperature dependent photoluminescence (PL). The base length of the QDs, calculated by the PL ground state transition energy, is in agreement with the atomic force microscopy measurements. By means of the excitation-dependent PL, we demonstrate that only the ground electron and hole states exist when the base length of the QDs is smaller than about 7.3 nm, whereas larger dots, with a base length of about 8.7 nm, give rise to one excited hole state. The measured energy separation between the ground and the excited hole states is in good agreement with the theoretical calculation. The transition energy in the temperature-dependent PL spectra shows a rapid redshift as the temperature is raised higher than the critical temperature. The redshift rate is about 2.8 and 2.5 times larger than the values calculated by Varshni's law for small and large dots, respectively. The higher redshift rate can be explained by the stronger tunneling effect. In addition, the PL linewidths show a V-shaped dependence on the temperature. This behavior can be described as a tunneling and electron-phonon scattering effect.
InGaAs/GaAs quantum wells and quantum dots on (111)B orientation
(2001)
Tyan, SL
;
Lin, YG
;
Tsai, FY
;
Lee, CP
;
Shields, PA
We report a magneto optical characterization of InGaAs/GaAs quantum well (QW) and quantum dot (QD) structures grown on (111)B GaAs substrates. The photoluminescence (PL) peak shift under high excitation intensity is used to distinguish QW from QD structures together with atomic force microscopy (AFM) imaging, The binding energy in(lll)InGaAs/GaAs QW is about 5 meV, The extent of the wave function obtained from the diamagnetic shift of the PL peak energy is consistent with the result calculated by the k,p method. The InGaAs/GaAs QD lateral confinement energy and the dot size are also estimated from the diamagnetic shift of the PL lines. The lateral confinement energy is estimated as 7 meV. The mean radius of the InGaAs QD is about 14 nm and the dot height is about 6 nm, which is in good agreement with the results as revealed in AFM imaging. (C) 2001 Published by Elsevier Science Ltd.
Magneto-photoluminescence study of InGaAs/GaAs quantum wells and quantum dots grown on (111)B GaAs substrate
(2000-06-01)
Tyan, SL
;
Shields, PA
;
Nicholas, RJ
;
Tsai, FY
;
Lee, CP
InGaAs/GaAs quantum well (QW) and quantum dot (QD) structures grown on GaAs (111)B substrates under different growing temperatures are investigated by magneto-photoluminescence (PL) up to 15 T in both Faraday and Voigt configurations. The spatial extents of the carrier wave functions (ECWFs) are deduced from the diamagnetic shift of the PL peak energy. The binding energies of the InGaAs/GaAs QWs are evaluated to be about 5 meV. The QW ECWFs in the growth direction obtained by the diamagnetic shift are consistent with those calculated by the k . p theory. The heights and radii of the InGaAs/GaAs QDs are also estimated from the ECWFs. In addition, we found that the in-plane ECWFs decreased slightly as the growth temperature was varied from 525 to 450 degrees C. The ECWFs in the growth direction decreased when the growth temperature was varied from 525 to 480 degrees C and then increased as the temperature was decreased to 450 degrees C.
Photoluminescence of ultra small InAs/GaAs quantum dots
(2005-08-10)
Lin, YG
;
Wu, CH
;
Tyan, SL
;
Lin, SD
;
Lee, CP
The InAs/GaAs quantum dots (QDs) with a baselength of less than 10 nm are studied by the excitation-, temperature-dependent and magneto-photoluminescence (PL). The baselengths of the QDs, calculated by the PL ground state transition energy and estimated by magneto-PL spectra, axe in agreement with the result of atomic force microscopy measurements. By means of the excitation-dependent PL, we demonstrate that only the ground electron and hole states exist when the baselength of the QDs is smaller than about 7.3 nm, whereas the larger dots with a baselength of about 8.7 nm will give rise to one excited hole state. The measured energy separation between the ground and the excited hole states is in good agreement with the theoretical calculation. The transition energy in temperature-dependent PL spectra shows a rapid redshift as the temperature is higher than the critical temperature. The redshift rate is about 2.8 and 2.5 times larger than the values calculated by Varshni's law for small and large dots respectively. The higher redshift rate can be explained by the stronger tunneling effect. In addition, the PL linewidths show a V-shape dependence with the temperature. This behavior could be well described as a tunneling and electron-phonon scattering effect.