C. Vieu

Evidence of stress dependence in SiO2/Si3N4 encapsulation-based layer disordering of GaAs/AlGaAs quantum well heterostructures

Spatial selectivity of layer disordering induced in GaAs/AlGaAs quantum well heterostructures using SiO2 and Si3N4 capping and annealing was investigated using low temperature photoluminescence in conjunction with cross-sectional transmission electron microscopy. Comparative study reveals opposite behaviors for patterned Si3N4 covered with SiO2 and patterned SiO2 covered with Si3N4. In the former, layer disordering occurs in the regions located under the SiO2 strips and in the latter, layer disordering surprisingly occurs under the Si3N4 strips while it is inhibited in the SiO2-capped areas. These results are in agreement with a proposed interdiffusion model based on the effect on Ga vacancy diffusion of the stress distribution generated in the heterostructure during annealing by the capping layers. This work clearly demonstrates that the diffusion of point defects, such as the Ga vacancies, which are responsible for the layer disordering, can be piloted by the stress field imposed to the semiconductor an...

Cross‐sectional high‐resolution electron microscopy investigation of argon‐ion implantation‐induced amorphization of silicon

Cross‐sectional high‐resolution transmission electron microscopy and related diffraction techniques are applied to the characterization of argon implantation‐induced amorphization of silicon at room temperature. Damage calculations have been performed to provide a theoretical support for the cross‐sectional transmission electron microscopy observations. It is shown that the amorphous‐crystalline interfacial roughness is strongly dependent on ion dose and hence on its depth location. The a‐c transition region was found to have sharply defined boundaries and sometimes exhibits defects such as dislocations and stacking‐fault nuclei. Combining the experimental measurement of the extension of the a layer for increasing dose, with concepts arising from the ‘‘critical damage energy density’’ model leads to a value of about 10 eV/atom for the c→a transformation. It is suggested that temperature effects are responsible for the observation that higher damage energy densities are apparently needed to produce a first...

Temperature behavior of multiple tunnel junction devices based on disordered dot arrays

Nanometer-sized multijunction arrays are expected to exhibit a large Coulomb blockade effect. However, up to now, only highly disordered arrays can be fabricated. In this article, we evaluate the consequences of disorder on the dispersion of the device characteristics. We show that, as observed for regular arrays, the threshold voltage Vth increases with the length of the multijunction array. At very low temperature, the Vth dispersion is small. Conversely, at higher temperature, a large dispersion in Vth is observed. We evidence the importance of the different array parameters with respect to the device characteristics. We show that the crucial parameters are the tunnel resistances and, therefore, for a two-dimensional array, the total resistance of the minimal resistance path is the most relevant parameter.

New characterization method of ion current‐density profile based on damage distribution of Ga+ focused‐ion beam implantation in GaAs

A new method is reported for characterizing focused ion probe current distributions based on the comparison between damage simulations and transmission electron microscopy observations. Several focused‐ion beam operation conditions were modeled, such as low‐to‐high source emission currents and variable beam acceptances. At low current and small acceptance, the ion spot exhibits a nearly Gaussian profile, otherwise larger tails are evidenced which can be modeled either by Pearson or ‘‘bi‐Gaussian’’ distributions. The sensitivity of the procedure to the tail extension is highlighted.

Optical characterization of selectively intermixed GaAs/GaAlAs quantum wires by Ga+ masked implantation

Quantum wires were fabricated by selective intermixing of a GaAs/GaAlAs quantum well through masked Ga+ implantation and rapid thermal annealing. The evolution of the luminescence spectra of the wires with the width of the implantation masks, enabled us to characterize the lateral selectivity of our process as well as the degree of one‐dimensional confinement. The lateral extent of the intermixing was estimated at 20 nm giving rise to an important penetration of aluminum into the wires. From numerical simulations of the spatial distribution of implantation‐induced damage, it was concluded that some lateral diffusion of the defects occurred during annealing. However it has been possible to assess the confinement energies to be around 4 meV. The linewidth of the wires’ emission turned out to increase with decreasing mask size, indicating the presence of some fluctuations of the confining potential along the wires. The roughness of the lateral definition of the wires was evaluated at 20 nm, of the same order...

Large‐Scale Assembly of Single Nanowires through Capillary‐Assisted Dielectrophoresis

An innovative technique is proposed for the precise and scalable placement of 1D nanostructures in an affordable manner. This approach combines the dielectrophoresis phenomenon and capillary assembly to successfully align thousands of single nanowires at specific locations at the wafer. The nanowires are selectively trapped by taking advantage of the material--specific frequence dependence.

Electron transport in metallic dot arrays: Effect of a broad dispersion in the tunnel junction dimensions

We have shown that for a one-dimensional multijunction array with a broad junction length distribution, we can increase the mean threshold voltage Vth for a given maximal tunnel resistance without increasing the scatter of Vth. For two-dimensional arrays we can increase strongly the output of devices which do not behave as open circuits, without any loss on the scatter on Vth, and still increase the latter with respect to a single-island device. The experimental background which justified the calculation will be described, as our model needs the experimental distribution of the island dimensions and junction lengths. Such a result may either show a way to increase the threshold voltages for a given technology, or allow for larger and therefore more controllable dimensions, or even extend the choice of materials.

Formation of 2-D arrays of semiconductor nanocrystals or semiconductor-rich nanolayers by very low-energy Si or Ge ion implantation in silicon oxide films

Abstract The structure evolution of annealed low-energy Si- or Ge-implanted thin and thick SiO2 layers is studied. The majority of Si (or Ge) species is restricted within a 3–4 nm thick layer. Si is able to separate and crystallize more easily than Ge. The glass transition temperature of the as-implanted structure has a significant effect on the progress of phase transformations accompanying annealing.

Optimization of experimental operating parameters for very high resolution focused ion beam applications

We report an experimental procedure to optimize the current profile of a focused ion beam probe, with a special emphasis on high resolution applications. The optimized operating conditions are given for three specific cases: specimen thinning for electron microscopy, nanoetching, and nanolithography. We present high quality membranes for transmission electron microscopy, arrays of nanoholes with reproducible dimensions of 17 nm etched on a nickel membrane, and finally nanolithography operations with a 10 nm resolution. Due to the conventional design of our focused ion beam system, the operating conditions that we have established for each nanofabrication application, should be successfully applied to a wide variety of ion columns.

A direct and fast computing method for damage energy depth distribution in ion implanted materials

Abstract A theoretically simple and computationally fast method for calculating damage energy density distributions for ions implanted into noninsulating materials is presented. The effect of the energy transported by the recoiling target atoms is taken into account in order to extend the calculation to lower energies and the near-surface target region. It is found that the results obtained over energy and mass ranges of interest for ion implantation experiments are in good agreement with previously reported experimental and calculated “damage” distributions. Special emphasis is placed upon applications to surface studies, sputtering and amorphization of Si(111) surfaces, as recently reported in a REM study.