Excitonic interband optical transitions within single InAs self-assembled quantum dots have been directly observed in a transmission experiment at 4.2 K. Using Stark shift, the excitonic energy levels of a single quantum dot are tuned into resonance with a narrow-band laser line. The Stark shift is also modulated at low frequencies. Relative changes in transmission can be detected this way down to one part per million. The oscillator strength as well the homogeneous linewidth of the transition is obtained.

InAs self-assembled quantum wire structures have been grown on InP substrates and studied by means of photoluminescence and polarized-light absorption measurements. According to our calculations, the observed optical transitions in each sample are consistent with wires of different heights, namely from 6 to 13 monolayers. The nonradiative mechanism limiting the emission intensity at room temperature is related to thermal escape of carriers out of the wires.

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ZnO films have been grown on gold (111) by electrodeposition using two different OHsources, nitrate and peroxide, in order to obtain a comparative study between these films.The morphology, structural and optical characterization of the films were investigated depending on the solution used (nitrate and peroxide) and the applied potential. Scanning Electron Microscopy pictures show different morphologies in each case. X-Ray Diffraction confirms that the films are pure ZnO oriented along the (0002) direction.ZnO films have been studied by photoluminescence to identify the emission of defects in the visible range. A consistent model that explains the emissions for the different electrodeposited ZnO films is proposed. We have associated the green and yellow emissions to a transition from the donor OHto the acceptor zinc vacancies (V Zn -) and to interstitial oxygen (Oi 0 ), respectively. The orange-red emission is probably due to

We have studied the emission and absorption properties of type II GaSb/ GaAs quantum dots embedded in a p-i-n photodiode. The excitation power evolution provides clear signatures of the spatially separated confinement of electrons and holes in these nanostructures. We have estimated the confinement potential for the holes to be ϳ500 meV, leading to an intense room temperature emission assisted by recapture processes from the wetting layer. Photocurrent measurements show strong absorption in the wetting layer and in the quantum dots at room temperature which are important for photodetection applications based in this system. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2827582͔In recent years, GaSb/ GaAs structures have aroused great interest due to their type II band alignment and intrinsically different behavior compared to the well known InAs/ GaAs system. Fundamental issues regarding their growth process, energy level structure, and optical properties in addition to their technological applications in photodetection and photovoltaics have been already investigated in different configurations such as quantum dots ͑QDs͒, 1-5 quantum wells 6 ͑QWs͒ or ternary compounds. 7 In this work, we present various results regarding the GaSb/ GaAs QDs system, which extend and complete previous works.The QDs studied here were grown by solid source molecular beam epitaxy on a n-type GaAs͑001͒ substrate after deposition of a n-type GaAs buffer layer ͑Si: 1 ϫ 10 18 cm −2 ͒. The QDs were nucleated at 480°C, using a growth rate of 0.1 ML/ s. The formation of the GaSb QDs was detected by the change of the reflection high energy electron diffraction pattern after the deposition of 1.3 ML of GaSb. The GaSb layer, with a nominal thickness of 2 ML, was then exposed to Sb flux for 20 s and then annealed for 20 s without an Sb flux to limit the amount of Sb segregated during capping. The GaAs capping was done at 0.4 ML/ s in two steps. In the first step, a 10 nm thick GaAs layer was grown at the temperature of QD nucleation to avoid their destabilization. In the second one, a 40 nm thick GaAs layer was deposited at 570°C. During growth, the As and Sb beam equivalent pressures were 1.0ϫ 10 −5 and 1.9ϫ 10 −6 mbar, respectively. This scheme was repeated six times, with a 3 min growth interruption under an As 4 flux to lower the substrate temperature before the nucleation of the next QD layer. On top, a p-type 300 nm thick GaAs layer ͑Be: 1 ϫ 10 18 cm −2 ͒ was grown at 580°C. Finally, standard optical lithography and wet etching techniques were used to define mesas and metal Ohmic contacts. Figure 1͑a͒ shows the photoluminescence ͑PL͒ spectra recorded at 20 K as a function of excitation power at 532 nm. We can clearly identify two bands centered at 1.32 and 1.05 eV. The narrow high energy band corresponds to the wetting layer ͑WL͒ recombination and dominates the spectrum at low temperatures. Its peak energy position is compatible with a GaSb WL thickness of 0.7 nm, 2 which is larger than the total amount of GaSb deposited ͑0.57 nm͒...

We report on the growth by molecular beam epitaxy and the study by atomic force microscopy and photoluminescence of low density metamorphic InAs/InGaAs quantum dots. subcritical InAs coverages allow to obtain 10 8 cm −2 dot density and metamorphic In x Ga 1−x As ͑x = 0.15, 0.30͒ confining layers result in emission wavelengths at 1.3 m. We discuss optimal growth parameters and demonstrate single quantum dot emission up to 1350 nm at low temperatures, by distinguishing the main exciton complexes in these nanostructures. Reported results indicate that metamorphic quantum dots could be valuable candidates as single photon sources for long wavelength telecom windows.

We present a fabrication method to produce site-controlled and regularly spaced InAs/GaAs quantum dots for applications in quantum optical information devices. The high selectivity of our epitaxial regrowth procedure can be used to allocate the quantum dots only in positions predefined by ex-situ local oxidation atomic force nanolithography. The quantum dots obtained following this fabrication process present a high optical quality which we have evaluated by microphotoluminescence and photon correlation experiments.

Photoluminescence and excitation of the photoluminescence spectroscopy has been performed in single InGaAs self-assembled quantum rings embedded in a field effect structure device. To determine their electronic structure, bias-dependent optical transitions have been analyzed both, for individual quantum rings, and for the averaged ensemble. Our results are compared with a theoretical model, and also with results reported by other authors studying similar nanostructures.