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There is a solid consensus that new methods of structure fabrication, placement, and organization within the sub-10-nm resolution gap are urgently required to meet existing challenges in condensed matter, semiconductors, and biotechnologies. Standard top-down methods such as resist-based lithographies even used at the shortest available wavelengths have clearly identified limitations. On the other hand, bottom-up approaches, like scanning probe manipulation techniques, remain challenging when trying to generate reproducible, functional, and addressable nano-structures. Therefore, at the laboratory level new routes must be explored. [ABSTRACT FROM PUBLISHER]

The authors studied the dry-etching process by chlorine-based inductively coupled plasma for fabricating GaAs suspended photonic crystal cavities. To achieve low optical loss in such resonators, the photonic crystal holes must demonstrate simultaneously smooth sidewalls and good verticality. The influence of various parameters of the inductively coupled plasma process was investigated: a systematic analysis is provided on the dependency of hole sidewall roughness and shape on the process parameters such as gas mixture, etching power, pressure, and rf bias. The authors show that a combination of high pressure, high bias, and high etching power in an inductively coupled plasma with a Cl2/N2 chemistry is beneficial for achieving straight and smooth sidewalls, and wall tilt of less than 4° was obtained. [ABSTRACT FROM AUTHOR]

Abstract: This article reports the first synthesis of fluorine nanoparticles composing K1− x (Y,Ln) x F1+2 x (with 0.56< x <0.73 and Ln=Er3+ or Eu3+) via a room temperature, coprecipitation method in aqueous solution. Nanoparticles with a fluorite-type structure are prepared using synthesis conditions that are highly flexible in terms of stoichiometry, acidity, concentration, fluorine source and reaction time. Those highly reactive nanoparticles can be considered as good precursor to achieve transparent ceramics for laser applications: the cubic symmetry is preserved upon heating despite large concentration of doping rare earth (0–15%). This method is much greener that traditional preparations for such fluorine materials, being carried out in water and avoiding the use of toxic, corrosive and more expensive fluorine sources such as HF or CF4 and SF6 gas. Nonetheless, the amount of oxygen in these materials is low, with absorbed water molecules and trapped hydroxyl groups effectively being removed above 450°C. Finally, we report the luminescence properties of the erbium doped materials, showing that materials presenting long decay times can be achieved via this route. [Copyright &y& Elsevier]

Abstract: GaAs nanowire (NW) heterostructures with four GaAsSb inserts were grown on GaAs(111)B substrates by Au-assisted molecular beam epitaxy (MBE). Structural characterization of the NWs showed that the transition between the GaAs and GaAsSb heterojunction is atomically abrupt and that the GaAs crystallographic phase is mainly wurtzite with some stacking faults, whereas the GaAsSb phase is zinc blende and free from twinning defects. Interestingly, the growth rates of the GaAs segments and GaAsSb inserts were observed to vary with growth time. We attribute this behavior to the effect of the inclined molecular beams with respect to the substrate surface in the MBE growth chamber. Further, the mole fraction of Sb in the GaAsSb insert was determined by energy-dispersive X-ray spectrometry and was found to increase with the inserts position along the NW. [Copyright &y& Elsevier]

HBr inductively coupled plasma (ICP) etching is investigated to realize ridge laser waveguides on InP and GaAs substrates. It has been reported that pure HBr chemistry leads to undercut ridge profiles when a hard dielectric mask is used. In this paper we show that a passivation layer can build up on the sidewalls and prevent lateral etching at high ICP powers if a Si wafer is used as the sample tray. Ex situ energy-dispersive X-ray analysis coupled to transmission electron microscopy shows that the passivation layer is a Si-rich silicon oxide. Vertical sidewalls, a smooth etched surface, and a moderate etch rate compatible with the processing of shallow ridge lasers can be obtained for lnP-based heterostructures. The optimized HBr etching process is used to etch InAs quantum dot shallow ridge lasers grown on lnP(100) substrate and compared to a classical HCI selective chemical etch. The waveguide losses of the HBr-etched waveguide do not differ from those of the chemically etched waveguide by more than 1 cm[sup-1]. Finally, we show that a similar passivation mechanism can be obtained during HBr ICP etching of GaAs/AlGaAs ridge waveguides, demonstrating that the same HBr (-O[sub2]) chemistry is suitable for both GaAs and InP systems. [ABSTRACT FROM AUTHOR]

The formation of axial heterostructures in filamentary nanocrystals (nanowhiskers) is considered within the framework of a two-component diffusion growth model. An expression for the thickness of a heteroboundary is obtained, which is consistent with the available experimental data. Under the usual growth conditions, the thickness of the zone of diffusion smearing of the heteroboundary is on the order of one atomic monolayer, which ensures the high quality of heteroboundaries in nanowhiskers. [ABSTRACT FROM AUTHOR]

The etching for InP photonic crystal (PhC) hole structure using Cl2/BCl3/N2 and BCl3/N2 inductively coupled plasmas has been investigated for the fabrication of membrane devices. The addition of N2 into Cl2-based plasma is shown to enhance the anisotropic etching and to suppress the sidewall roughness compared to the Cl2/Ar plasma. The profile verticality of PhC structures is improved by the introduction of BCl3. The smooth sidewalls and the vertical hole profiles are obtained when N2 ratio (N2 mass flow rate/total gas flow) is superior to 65%. Positive ion fluxes are measured with the variations of gas flow rates for the plasma characterization. It is found that the addition of N2 to the Cl2/BCl3 plasma can cause a decrease in positive ion density when the N2 ratio is more than 20%. Chemical identification of the InP surface after etching by a N2-based plasma is characterized by transmission electron microscopy, and no nitrogen element is observed along the sidewalls, which indicates a low probability of surface passivation through N2. By the time-resolved photoluminescence measurement, free-carrier lifetime of 1400 ps is obtained on InP/InGaAsP quantum wells with PhC structures etched by an inductively coupled plasma Cl2/BCl3/N2 plasma, which is beneficial for active devices fabrication. Furthermore, InP photonic crystal membrane defect waveguide with one missing row (W1) is fabricated and shows a low propagation loss value of 25 dB/cm while operating below the air-light line. [ABSTRACT FROM AUTHOR]

We demonstrate the feasibility and flexibility of artificial shape engineering of epitaxial semiconductor nanostructures. Novel nanostructures including InGaAs quantum rods (QRs), nanocandles, and quantum dots (QDs)-in-rods were realized on a GaAs substrate. They were formed by depositing a short-period GaAs/InAs superlattice (SL) on a seed QD layer by molecular beam epitaxy growth. The InAs layer thickness in the SL plays an important role in obtaining the QRs. The growth of the QRs is very sensitive to growth interruption and growth temperature. By properly choosing both growth parameters, QRs with length of 41 nm corresponding to an extremely large aspect ratio of 4.1 were obtained. The evolution from a 0-D to 1-D confinement type is evidenced in the optical properties. The origin of the optical transitions from the QRs was understood by calculations of the electronic states within a fully 3-D approach in the eight-band kcdotp approximation. The QRs are embedded in a GaAs matrix and are therefore free from surface traps. This feature enables high material quality and consequently their application in real devices. At room temperature, laser diodes based on QR active regions lasing around 1120 (or 1130) nm are demonstrated. [ABSTRACT FROM PUBLISHER]

Energy dispersive x-ray (EDX) spectroscopy coupled to transmission electron microscopy (TEM) is used to analyze the passivation layer deposited on the sidewall of InP submicron patterns etched in Cl2–H2 and HBr inductively coupled plasmas. It is shown that a thin Si-containing layer is deposited on the sidewalls of the etched patterns, resulting from the reaction of Cl2 or HBr with the Si wafer used as the sample tray. For Cl2-containing plasma, the deposition layer becomes thicker when hydrogen is added to the gas mixture, leading to highly anisotropic InP etching at an optimized H2 percentage. A similar effect is obtained in HBr plasma by increasing the ICP power. When O2 is added to the gas mixture, the deposited layer is changed from Si rich to more stoichiometric silicon oxide (SiO2) and the passivation effect is enhanced. EDX-TEM analysis has also been carried out on InP samples etched in Cl2–N2 plasma for comparison. A similar impact of the coverplate material on the sidewall profile is evidenced, the InP sidewall being moreover strongly In deficient in this case. These results give useful guidelines to define anisotropic etching processes scalable to large-diameter InP wafers. [ABSTRACT FROM AUTHOR]

Abstract: The growth of self-organized InAs(N) quantum dots on GaAs by molecular beam epitaxy has been investigated. Photoluminescence (PL) and transmission electron microscopy (TEM) experiments have been carried out to determine the influence of the growth temperature and nitrogen plasma exposure on the optical and structural properties of the dots. At low growth temperature, in the 410–450°C range, some nitrogen is found to be incorporated in the quantum dots. This incorporation does not significantly affect their shape but causes a red-shift of the PL emission. At higher temperature, 510°C, a bimodal distribution rapidly appears with nitrogen exposure. Cross-sectional TEM images reveal a first population of coherent dots whose shape is similar to that of InAs dots, and a second population of large, flat and occasionally relaxed dots; in that case the associated PL spectrum is typical of low density arrays of N-free InAs quantum dots. Discussion focuses on the different mechanisms involved in the dots growth. It is proposed that the occurrence of the second population of large dots is due to the defects and composition fluctuations induced by nitrogen at 510°C. [Copyright &y& Elsevier]

Oxyfluoride glasses (GeO2-PbO-PbF2) doped with erbium and/or ytterbium fluorides were prepared. Highly transparent glass-ceramics, containing β-PbF2 nanocrystallites, were successfully obtained by controlled glass devitrification and were studied as they could lead to promising optical applications. To characterize the samples, differential thermal analysis, x-ray diffraction, and transmission electron microscopy were performed, revealing a variation of the crystallites size, the crystallites number and β-PbF2 crystallization temperature according to the doping ion. Indeed, the analyses indicated differences between erbium and ytterbium fluorides in promoting the crystallization of the fluoride phase. Although both fluorides act as seeds for β-PbF2 heterogeneous nucleation, erbium fluoride has higher nucleation efficiency than ytterbium fluoride and runs the nucleation process in co-doped samples. Energy dispersive x-ray microanalysis insured high rare-earth segregation into the crystallites, proving the formation of a solid solution Pb1-x-yErxYbyF2 + x+y, also confirmed by the unit cell parameter study. [ABSTRACT FROM AUTHOR]

The article reports that fast recovery time is a key parameter for the design of new high transmission rate optical devices, like ultrafast optical switches for telecommunication applications. Optical switches can consist of semiconductor saturable absorbers that regenerate the optical signal by excitonic absorption in a QW-based structure. To reach high transmission capacity, the essential parameter for saturable absorbers is the recovery time after absorption, which is governed by the carrier recombination rate and is typically around a few ns for semiconductors.

Ordered In x Ga 1 - x P alloys have been grown on to GaAs(001) substrates by metal-organic vapour-phase epitaxy. Lattice-matched compositions of alloys (In x Ga 1 - x P with x ≈ 0.5) were used in order to produce epitaxial layers free of structural defects (threading dislocations). Growth temperature and substrate orientation were adjusted to control the degree η, of order, of the alloys in the range 0.3-0.5. Nanoindentation tests were carried out to measure the mechanical response of the heteroepitaxial layers. Transmission electron microscopy was used to characterize the structure as well as the plastic zones generated into the specimen by nanoindentation. Comparison of the alloys with binary references (InP and GaP bare substrates) showed strengthening, with the hardness and flow-stress values that are much larger than those of InP and of the same order of magnitude as those of GaP. [ABSTRACT FROM AUTHOR]

Indentation tests were performed at a high temperature on GaAs(011). This orientation allowed the activation of normal and inclined slip systems. Samples with two different thicknesses were prepared and a large range of loads was used. Observations on decreasing scales were carried out using different microscopies and more particularly transmission electron microscopy on thin foils prepared by the focused-ion-beam technique. The back side of the thinnest samples could be deformed using the highest loads. The deformation was observed to be anisotropic on the back side as well as at the indented surface. On one side of the indentation, an anisotropic climb of matter was revealed and associated with microtwinning development. Convergent-beam electron diffraction as well as chemical etching allowed us to determine rigorously the polarity of the samples and the character of dislocations (α or β) generated by the indenter. The dislocations extending deeper into the samples were determined to be α dislocations. This result was discussed in view of the difference between the core reconstructions and mobilities of α and β dislocations. [ABSTRACT FROM AUTHOR]

MBE-grown GaInNAs quantum wells (QWs) with and without surrounding GaNAs layers were investigated comparatively. It was demonstrated that introducing GaNAs layers extends efficiently its emission wavelength. However, at a given emission wavelength, the GaNAs intermediate layers do not help to improve the quality of the structure: photoluminescence characteristics are similar for both type of structures, but the GaNAs-containing QW was more sensitive to thermal treatment. Furthermore, the GaNAs-containing QW showed slightly inferior structural quality at the upper interface between compressive GaInNAs and tensile GaNAs layers. In these samples, the photoluminescence blue-shifts are believed to be predominantly determined by interdiffusion phenomena. [Copyright &y& Elsevier]

We have studied the changes generated by a post-annealing treatment of a nanoindentation structure realized on GaAs(001). The nanoindentations were made under a large range of loads (between 0.5 and 10 mN) at room temperature and were subsequently annealed at 500°C for 1 h. Transmission electron microscopy was used to observe the nanoindentation structures before and after annealing. The size of the dense plastic zone generated around the indent site decreased by about 20% after annealing and rosette arms propagated along the 〈110〉 directions parallel to the indented surface. Not only were the lengths of the rosette arms multiplied by a factor of three after the annealing process but also the arrangement and structure of the dislocations drastically changed. The hairpin dislocations starting from the side of the indents observed before annealing transformed into alignments of half-loop dislocations. Furthermore, no partial dislocations were observed after the annealing whereas some of these could be detected before annealing. [ABSTRACT FROM AUTHOR]

Nanoindentation has been used to explore the plasticity onset under contact loading in InP. Under low indenting loads ranging between 0.2 and 10 mN, fracture of the sample is avoided and plastic zones can be observed by transmission electron microscopy. The zone-size variation with load could be measured and analysed using the work of Johnson and of Kramer et al. The results were compared with those obtained in GaAs deformed under the same conditions. Furthermore, characterization of the dislocations was made and it was shown that the twinning formation in InP differed strongly from that in GaAs. The results are compared with previously reported arrangements obtained in the microindentation domain. [ABSTRACT FROM AUTHOR]

Compliant structures have been fabricated in which a thin GaAs layer (thickness between 10 and 20nm) was bonded on top of a GaAs substrate with a large twist angle (about 37°). This twist angle value was chosen so that the energy of the boundary (coincident boundary of type Σ =5 (001)) was minimized. The structure of the interface was characterized and the onset of plasticity in such a compliant substructure was investigated using nanoindentation that allowed the low-load deformation regime to be observed. The results are compared with those obtained under the same conditions on a GaAs bulk substrate alone. No plastic zone was observed by transmission electron microscopy in the compliant structure under loads below 0.25mN while, under the same loads, plastic deformation was observed in the bulk substrate. For higher loads (2mN), plastic-flow enhancement was observed in the compliant structure. The results are discussed in the light of the arrangement of dislocations observed in the plastic zones. [ABSTRACT FROM AUTHOR]

(001) surfaces of InP single crystals have been deformed at room temperature by a Vickers indentor submitted to a load of 1 N. The indents formed were observed by transmission electron microscopy (TEM) in cross-sectional views obtained by the focused-ion beam (FIB) technique. The structure of the plastic zone has been investigated and the different modes of plastic deformation involved during the deformation have been analysed. The flow stress of InP was estimated and compared to the reported values in the literature. [ABSTRACT FROM AUTHOR]

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