New GaAs quantum dot structures, called tetrahedral quantum dots (TQDs), are proposed to make a zero‐dimensional electron‐hole system. The TQDs are surrounded by crystallographic facets fabricated using selective area metalorganic chemical vapor deposition (MOCVD) on (111)B GaAs substrates. The calculated energy sublevel structures of zero‐dimensional electrons in a GaAs TQD show large quantum size effects, because electrons are confined three dimensionally. GaAs and AlGaAs tetrahedral facet structures on (111)B GaAs substrates partially etched into a triangular shape were grown using MOCVD. Tetrahedral growth with {110} facets occurs in the triangular areas. The cathodoluminescence intensity map for GaAs tetrahedrons buried in AlGaAs shows the tetrahedral dot array.

GaAs tetrahedral quantum dot structures fabricated using selective area metalorganic chemical vapor deposition

Intermixing the wells and barriers of quantum-well (QW) laser heterostructures generally results in an increase in the bandgap energy and is accompanied by changes in the refractive index. A technique, based on ion implantation-induced QW intermixing, has been developed to enhance the quantum-well intermixing (QWI) rate in selected areas of a wafer. Such processes offer the prospect of a powerful and simple fabrication route for the integration of discrete optoelectronic devices and for forming photonic integrated circuits.

Photonic integrated circuits fabricated using ion implantation

In this topical review, the potential of the focused ion beam (FIB) technology and ultimate applications are reviewed. After an introduction to the technology and to the operating principles of liquid metal ion sources (LMIS), of ion optics and instrument architectures, several applications are described and discussed. First, the application of FIB for microcircuit inspection, metrology and failure analysis is presented. Then, we introduce and illustrate some advanced patterning schemes we propose as next generation FIB processing examples. These patterning schemes are (i) local defect injection or smoothing in magnetic thin film direct patterning, (ii) functionalization of graphite substrates to guide organization of clusters, (iii) local and selective epitaxy of III‐V semiconductor quantum dots and (iv) FIB patterned solid-state nanopores for biological molecules manipulation and analysis. We conclude this work by giving our vision of the future developments for FIB technology. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0268-1242/24/4/043001/pdf

Focused ion beam technology and ultimate applications

We have been able to fabricate a two‐dimensional electron gas containing an atomically precise, lateral Kronig–Penney potential of 102 A periodicity. The structure was formed by modulation‐doped molecular beam epitaxy overgrowth on the cleaved edge of a 71 A GaAs/31 A AlGaAs compositional superlattice. Low‐temperature magnetotransport reveals clear quantum Hall characteristics. From the onset of the Shubnikov–de Haas oscillations at 0.25 T we deduce a lower limit of the mobility of μ≳40 000 cm2/V s at an electron density of 3.0×1011 cm−2 and infer that the carriers are crossing more than 200 GaAs/AlGaAs interfaces without losing phase coherence.

Atomically precise superlattice potential imposed on a two-dimensional electron gas

InGaAs/GaAs/AlGaAs and InGaAs/InGaAsP/InP laser structures, with InGaAs quantum wells approximately 1.85 μm beneath the surface, were implanted with ions having energies up to 8.6 MeV. Intermixing of the quantum wells, after rapid thermal annealing, was monitored through changes in the energy, linewidth, and intensity of the photoluminescence peak from the quantum wells. Where the defects had to diffuse primarily through Al0.71Ga0.29As, these quantities correlate strongly, for short anneal times, with calculated vacancy generation and ion deposition at the depth of the quantum well prior to annealing. This suggests that the defect diffusion length in the AlGaAs and/or GaAs is quite low. For diffusion primarily through InP, the photoluminescence data correlated well with the calculated total number of vacancies created in the sample, suggesting that defect diffusion is very efficient in InP.

Defect diffusion in ion implanted AlGaAs and InP: Consequences for quantum well intermixing

We show that focused ion beam implantation of Ga into GaAlAs/GaAs quantum wells occurs much deeper than expected from theory of implantation into amorphous GaAs and that the lateral straggling is one order of magnitude smaller than predicted by the same theories. We show that channeling is the main mechanism involved in these effects. The small probe size achieved with the focused ion beam is thus preserved 200 nm below the surface.

Focused ion beam channeling effects and ultimate sizes of GaAlAs/GaAs nanostructures

A high‐energy (up to 150 keV) Ga+ focused ion beam is used to implant quantum well structures and interdiffuse GaAs/GaAlAs heterojunctions thus creating quantum wires and boxes. We investigate the optical properties of these structures using low‐temperature cathodoluminescence. Wires as wide as 800 A have been observed 2000 A below the surface. We study the optical damage and the interdiffusion process as a function of the implantation parameters (ion energy ion dose) and as a function of the rapid thermal annealing time. A universal correlation between the optical damage and the interdiffusion length has been found. The optimum process conditions are proposed.

F. Laruelle

Papers

Focused ion beam channeling effects and ultimate sizes of GaAlAs/GaAs nanostructures

Implantation enhanced interdiffusion in GaAs/GaAlAs quantum structures

Optical study of GaAs/GaAlAs quantum structures processed by high energy focused ion beam implantation