Fundamental Research Division
The DRF at the CEA assemble approximately 6,000 scientists since January 2016.
Scientific result | Micro-nanotechnologies
Researchers from IRIG [collaboration] publish their solution to create an interface between two crystals without generating dislocations, even though their mesh parameters differ by several percent. This work opens up new possibilities for integrated optoelectronics and photonics on silicon.
Some of the toughest substances on Earth are crystals, in which planes of atoms arrange themselves in lattices held together by chemical bonds. Deforming a crystal is difficult without breaking bonds which degrade materials performance, be it for sturdiness such as in a bridge, or more subtle properties – for example the performance of a laser or a computer chip, where light or electrical current can stumble over defects created in a crystal. Heterostructures, or interfacing two semiconductor crystals, have sparked a high degree of interest since the creation of the first laser diodes as they form the backbone of optoelectronic and photonic devices.Different crystals show a different organization of lattices. This results in a different atomic spacing or a different mesh parameter. When a junction is artificially created between two crystals, a natural way for materials to compensate for the difference in their atomic spacing is to compress and expand their crystal lattice at the interface, creating a mechanically stressed region, but this is also a way of introducing defects known as dislocations.
After having developed InAs-on-GaAs nanowire heterostructures on silicon, researchers from the IRIG, in collaboration with the Néel Institute, TU Eindhoven and the C2N, are publishing their solution to create an interface between two crystals making sure that no dislocations are formed.
They succeeded by using semiconductor nanowires, which are wire-shaped crystals smaller than a thousandth of the thickness of a human hair. In a nanowire there are few atoms in the cross-section, therefore, it is easier to deform the lattice. These nanowires grow as a forest on a silicon wafer.
Two different materials can be easily combined even if their lattice parameter differ greatly (by several percent). Nevertheless, an excessive mechanical strain is not recommended, as it would strongly influence the electronic properties of the interface. Remarkably, the researchers obtain a stress reduction of several percent in the case of an interface of a few nanometers between the two crystals (formed by an alloy whose composition gradually varies from one material to another).
They performed chemical and structural characterization of the interface by combining energy dispersive X-ray spectroscopy and high-resolution transmission electron microscopy. These experimental results are also compared with finite element calculations. The team confirm this very strong reduction in mechanical stress at the junction between two technologically important semiconductors: InAs and GaAs.Finally, this work broadens the parameter space for the design of nanowire heterostructures, thus opening up new possibilities for integrated optoelectronics and photonics on silicon.
Full characterization and modeling of graded interfaces in a high lattice-mismatch axial nanowire heterostructure, Physical Reviews Materials
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.