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.

International audienceIn this paper we present a review on major advances achieved over the past ten years in the field of fabrication of semiconductor quantum wires (QWRs) using epitaxial growth techniques and investigation of their optical properties. We begin the review with a brief summary on typical epitaxial QWRs developed so far. We next describe the state-of-the-art structural qualities of epitaxial QWRs in terms of (i) size uniformity between wires, (ii) heterointerface uniformity, (iii) crystal purity, and (iv) strength of lateral quantum confinement. Several prominent breakthroughs have been accomplished concerning the improvements of wire qualities, including (i) realization of V-shaped GaAs/AlGaAs QWRs in the ``real one-dimensional'' (1D) regime in which exciton states can extend coherently over distances exceeding 1 mu m, (ii) reduction of residual impurity concentrations in V-shaped GaAs/AlGaAs QWRs to a level comparable to that in an equivalent quantum well (QWL), which resulted in the semiconductor QWR with room-temperature photoluminescence efficiency exceeding that of a QWL, and (iii) reduction of the multimonolayer (ML) interface fluctuations on the second-grown arm QWL surface, in old-generation T-shaped GaAs/AlGaAs QWRs, to the single-ML level. The second part of this article is devoted to the discussion of optical properties of epitaxial QWRs, such as exciton dynamics, fine structure of exciton levels, and nonlinear effects, studied by means of high-spatial resolution spectroscopy, i.e., microphotoluminescence experiments. We will concentrate our discussions on V-shaped GaAs/AlGaAs QWRs and put an emphasis on demonstrating how the interface quality influences wire's optical properties. The properties of QWRs in the ``zero-dimensional quantum box regime'' and QWRs in the real 1D regime will be presented in separate sections. We will show that the realization of QWRs in the real 1D regime makes possible the investigation of intrinsic 1D effects by focusing on a single perfect 1D wire region using microscopic techniques. This has led to important results, for instance, (i) the demonstration of the square-root dependence of 1D exciton radiative recombination lifetimes down to a temperature as low as 10 K (limited by the experimental setup) and (ii) the clear demonstration of the existence of Mott transition in a 1D exciton system which is a fundamental problem under long debate. (c) 2006 American Institute of Physics

Herein, a successful elimination of the size-dependent efficiency decrease in GaN micro-light-emitting diodes (micro-LEDs) is achieved using damage-free neutral beam etching (NBE). The NBE technique, which can obtain ultralow-damage etching of GaN materials, is used in place of the conventional inductively coupled plasma to form the micro-LED mesa. It is found that all the fabricated micro-LEDs with sizes ranging from 40 to 6 μm show external quantum efficiency (EQE) versus current density characteristics similar to those of large-area GaN LEDs, with a maximum in EQE curves at a current density of as low as about 5 A cm À2 . Furthermore, all the fabricated micro-LEDs, even the 6 μm one, show a similar value of maximum EQE with a variation of less than 10%, clearly indicating a negligible size dependence of emission efficiency of micro-LEDs fabricated by the NBE technique at least down to the size of 6 μm. These results suggest that the NBE process is a promising method of fabricating high-efficiency sub-10 μm GaN