| 1. |
- Amloy, Supaluck, et al.
(författare)
-
Dynamic characteristics of the exciton and the biexciton in a single InGaN quantum dot
- 2012
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 101:6
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of the exciton and the biexciton related emission from a single InGaN quantum dot (QD) have been measured by time-resolved microphotoluminescence spectroscopy. An exciton-biexciton pair of the same QD was identified by the combination of power dependence and polarization-resolved spectroscopy. Moreover, the spectral temperature evolution was utilized in order to distinguish the biexciton from a trion. Both the exciton and the biexciton related emission reveal mono-exponential decays corresponding to time constants of similar to 900 and similar to 500 ps, respectively. The obtained lifetime ratio of similar to 1.8 indicates that the QD is small, with a size comparable to the exciton Bohr radius.
|
|
| 2. |
- Holtz, Per-Olof, et al.
(författare)
-
Optical characterization of individual quantum dots
- 2012
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1472-1475
-
Tidskriftsartikel (refereegranskat)abstract
- Optical characterization of single quantum dots (QDs) by means of micro-photoluminescence (mu PL) will be reviewed. Both QDs formed in the Stranski-Krastanov mode as well as dots in the apex of pyramidal structures will be presented. For InGaAs/GaAs dots, several excitonic features with different charge states will be demonstrated. By varying the magnitude of an external electric or magnetic field and/or the temperature, it has been demonstrated that the transportation of carriers is affected and accordingly the charge state of a single QD can be tuned. In addition, we have shown that the charge state of the QD can be controlled also by pure optical means, i.e. by altering the photo excitation conditions. Based on the experience of the developed InAs/GaAs QD system, similar methods have been applied on the InGaN/GaN QD system. less thanbrgreater than less thanbrgreater thanThe coupling of LO phonons to the QD emission is experimentally examined for both charged and neutral excitons in single InGaAs/GaAs QDs in the apex of pyramidal structures. It is shown that the positively charged exciton exhibits a significantly weaker LO phonon coupling in the mu PL spectra than the neutral and negatively charged species, a fact, which is in consistency with model simulations performed.
|
|
| 3. |
- Hsu, Chih-Wei, et al.
(författare)
-
The charged exciton in an InGaN quantum dot on a GaN pyramid
- 2013
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 103:1
-
Tidskriftsartikel (refereegranskat)abstract
- The emission of a charged exciton in an InGaN quantum dot (QD) on top of a GaN pyramid is identified experimentally. The intensity of the charged exciton exhibits the expected competition with that of the single exciton, as observed in temperature-dependent micro-photoluminescence measurements, performed with different excitation energies. The non-zero charge state of this complex is further supported by time resolved micro-photoluminescence measurements, which excludes neutral alternatives of biexciton. The potential fluctuations in the vicinity of the QD that localizes the charge carriers are proposed to be responsible for the unequal supply of electrons and holes into the QD.
|
|
| 4. |
- Larsson, Arvid, 1979-, et al.
(författare)
-
Manipulating the Spin Polarization of Excitons in a Single Quantum Dot by Optical Means
- 2011
-
Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 98:7, s. 071906-
-
Tidskriftsartikel (refereegranskat)abstract
- Circular polarization studies of photoluminescence from the neutral (X0) and the positively charged (X+) exciton are reported for individual InAs/GaAs quantum dots (QDs). High polarization degrees, 60 % for X0 and 73 % for X+, were recorded without any external magnetic field applied. These studies show that that the QD polarization and population dynamics are controllable either by varying the photo-excitation intensity, or by using a second IR laser excitation.
|
|
| 5. |
- Moskalenko, Evgenii, et al.
(författare)
-
Circularly polarized emission from ensembles of InAs/GaAs quantum dots
- 2011
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 110:1, s. 013510-
-
Tidskriftsartikel (refereegranskat)abstract
- We present a low-temperature micro-photoluminescence (mu-PL) study of ensembles of InAs/GaAs quantum dots (QDs) with respect to its circular polarization (rho(c)) for a manifold of experimental conditions such as single or dual laser excitation, different excitation energies (h upsilon(ex)), varying excitation powers (P(ex)) of both lasers, and with or without an external magnetic field (B(ext)). It is demonstrated that an essential rho(c) (less than= 40%) could be recorded depending on P(ex), even at B(ext) = 0 for h upsilon(ex) exceeding the PL energy of the wetting layer (E(WL)), while rho(c) remains negligible for h upsilon(ex) less than E(WL). To explain the data obtained, a model is developed according to which a nuclear magnetic field (B(N)) is created in the QDs by spin-polarized electrons. The B(N) plays a crucial role in the preservation of the electron spin, which otherwise effectively relaxes due to the presence of the anisotropic electron-hole exchange interaction (omega(ex)). The application of an additional infra-red laser gives rise to a population of excess holes in the QDs, thus producing positively charged excitons. In this case, omega(ex) = 0 and accordingly, rho(c) approximate to 40% at B(ext) = 0 is recorded, even for excitation with h upsilon(ex) less than E(WL).
|
|
| 6. |
- Moskalenko, Evgenii, et al.
(författare)
-
Spin polarization of neutral excitons in quantum dots: the role of the carrier collection area
- 2010
-
Ingår i: Nanotechnology. - : Institute of Physics. - 0957-4484 .- 1361-6528. ; 21:34
-
Tidskriftsartikel (refereegranskat)abstract
- A high degree (approximate to 55%) of circular polarization has been observed for the neutral exciton in InAs/GaAs quantum dots (QDs). The possibility to record non- zero polarization of the neutral exciton is explained in terms of different capture times of the light electron compared with the heavier holes into the QDs from the wetting layer. This interpretation is supported by the progressive reduction of the polarization degree with increasing QD density, and also with increasing temperature.
|
|
| 7. |
- Moskalenko, Evgenii, et al.
(författare)
-
Spin polarization of the neutral exciton in a single quantum dot
- 2011
-
Ingår i: SUPERLATTICES AND MICROSTRUCTURES. - : Elsevier Science B.V., Amsterdam. - 0749-6036. ; 49:3, s. 294-299
-
Tidskriftsartikel (refereegranskat)abstract
- While efficient nuclear polarization has earlier been reported for the charged exciton in InAs/GaAs quantum dots at zero external magnetic field, we report here on a surprisingly high degree of circular polarization, up to approximate to 60%, for the neutral exciton emission in individual InAs/GaAs dots. This high degree of polarization is explained in terms of the appearance of an effective nuclear magnetic field which stabilizes the electron spin. The nuclear polarization is manifested in experiments as a detectable Overhauser shift. In turn, the nuclei located inside the dot are exposed to an effective electron magnetic field, the Knight field. This nuclear polarization is understood as being due to the dynamical nuclear polarization by an electron localized in the QD. The high degree of polarization for the neutral exciton is also suggested to be due to separate in-time capture of electrons and holes into the QD.
|
|
