A systematic study of exciton dynamics is presented in quantum boxes formed naturally along the axis of a V-shaped quantum wire, by means of time and spatially resolved resonant photoluminescence. The dependence of radiative lifetimes and relaxation mechanisms of excitons is determined versus the size of the boxes. The radiative recombination rate varies linearly with the length of the box, showing that the exciton has a coherence volume equal to the volume of the box. In a low excitation regime, emission from excited states has not been observed, which would be a consequence of relaxation bottleneck, but there is clear evidence that relaxation via emission of LA phonons depends strongly on the energy separation between the different quantum box level

We report on microscopic photoluminescence of a single V-shaped AlGaAs/GaAs quantum wire. The experiments are performed at low temperature by selectively exciting 1 mu m2 of the sample. The main photoluminescence line is split into sharp peaks of width less than 0.5 meV and separated by a few meV. The energy position and the intensity of the peaks, are characteristic of the scanned quantum wire. First microphotoluminescence results suggest that localization phenomena are predominant in the quantum wire. They are due to the formation of extended monolayer-step islands, larger than the exciton radius, as in the case of high-quality quantum well

Flow rate modulation epitaxy ͑FME͒ is applied to the low-temperature growth of AlGaAs/GaAs quantum wires ͑QWRs͒ on nonplanar substrates. The growth selectivity is found to be enhanced greatly by the use of FME, as compared with the conventional metalorganic chemical vapor deposition due to the enhanced migration of Ga species. An AlGaAs/GaAs QWR with a central thickness of about 9 nm and a lateral width of about 28 nm is grown at 600°C on a V-grooved substrate. Good photoluminescence properties are observed from the grown QWR, with the peak energy being in good agreement with the calculated energy level of a parabolic shape lateral confinement potential.Selective area epitaxial growth on a nonplanar substrate is one of the most intensively investigated techniques of fabricating high quality semiconductor quantum wires ͑QWRs͒ or quantum dots ͑QDs͒. Successful laser operation has been achieved with a metalorganic chemical vapor deposition ͑MOCVD͒ grown AlGaAs/GaAs QWR on a V-grooved substrate as the active layer. 1 This method depends on the lateral variation of growth rate on nonplanar substrates due to the different migration length of group III species on different crystalline facets. Therefore, a high selectivity of growth rate is desired to obtain ideal QWR or QD structures. For this purpose, a high growth temperature ͑Ͼ700°C͒ and a low V/III ratio are generally used to realize a high selectivity because such conditions can enhance the migration of group III species. 2-3 However, high growth temperature is not suitable for the fabrication of QWR or QD structures for electron device applications, since a growth temperature higher than 700°C usually leads to the increase of residual impurities in MOCVD growth. The lowest impurity concentration and highest carrier mobility are obtained at the temperature range of 600-650°C. 4 Therefore, fabrication of QWR or QD structures at the temperature range of 600-650°C is required when considering electron devices utilizing QWR or QD structures.In this letter, we report the successful growth of high quality AlGaAs/GaAs QWRs by using flow rate modulation epitaxy ͑FME͒ at a growth temperature as low as 600°C. The FME method was first developed by Kobayashi et al. [5][6][7] for low-temperature MOCVD growth of GaAs and was recently extended to the growth of other III-V semiconductors. 8 Figure 1͑a͒ shows the typical gas flow sequence of the FME growth. In FME growth, group III and group V gases, triethylgallium ͑TEGa͒ and AsH 3 in this work, are supplied alternatively to the substrate surface. To prevent evaporation of arsenic and impurity incorporation during TEGa flow period, a very small amount of AsH 3 indicated by r 0 is supplied throughout the growth. Due to the extremely low arsenic partial pressure during the TEGa flow period, Ga species can migrate very rapidly on the substrate surface, which is considered very important for the formation of QWRs. At a growth temperature of 550°C, GaAs epitaxial layers with crystalline quality higher than that of GaAs grown by convent...

The temperature dependence of photoluminescence (PL) properties of AlGaAs/GaAs quantum wire (QWR) grown on V-grooved substrates by flow rate modulation epitaxy is investigated. PL from a 7.1 nm thick QWR is easily observed even at room temperature. The full width at half-maximum (FWHM) of the QWR emission peak increases linearly with increasing temperature at low temperatures and becomes almost independent of temperature at high temperatures, while that of a quantum well layer (QWL) sample increases with increasing temperature up to room temperature. The FWHM of QWR is found to be considerably narrower than that of the QWL sample at high temperatures, which is expected theoretically from the sharp one-dimensional density of states of QWR but has not been clearly observed experimentally.

Effects of composition nonuniformity of an AlGaAs barrier layer on the carrier capture efficiency of an AlGaAs/GaAs quantum wire (QWR) grown on nonplanar substrates are investigated using photoluminescence measurements. The photogenerated carriers first experience a redistribution from the high Al composition region to the low Al composition region in the AlGaAs barrier layer due to the potential difference caused by the composition nonuniformity before they are captured by quantum well or QWR regions. Such a carrier redistribution greatly affects the carrier capture efficiency of QWR structures.