Antimonide quantum dots enable novel photonic devices

Abstract

Long-wavelength (i.e., near-IR) light-emitting devices, especially 1.3and 1.55μm lasers, are needed for ubiquitous fiberoptic communication networks. To achieve low-cost, low-power consumption and high performance from such light sources, we would like to fabricate them on low-cost, high-quality semiconductor substrates such as gallium arsenide and silicon wafers. But the crystal lattice mismatch between these substrates and narrow-energy-bandgap semiconductors makes it difficult to obtain near-IR light-emitting materials using normal fabrication techniques. Recently, some approaches for creating these luminescent materials have been proposed. As one method, the epitaxial growth of nitride-based semiconductors—such as GaInNAs— on GaAs substrates is being widely investigated. SiGe, silicon quantum dots (QDs), and III-V semiconductors bonded directly to Si are also being studied to find a photonics technology that allows us to fabricate light-emitting materials on Si. However, obtaining optimized material characteristics for highintensity and near-IR luminescence with these material fabrication techniques is also difficult. To avoid these difficulties, we used nanostructured semiconductors, such as a quantum dots (QDs), to create near-IR luminescent material on GaAs and Si substrates. Quantum dots have very interesting characteristics, including quantum confinement of carriers and high luminescent efficiency. In addition, QD structures can be grown without requiring lattice matching between the QDs and the substrate. Without this restriction, we are free to use antimonide-based III-V semiconductor materials, which have very narrow bandgaps. These materials were not used in the past because of the very large lattice mismatch (more than 10%) between Sb-based materials and GaAs or Si. Therefore, we created Sb-based III-V semiconductor QD structures (i.e., the Sb atoms are included in Figure 1. Atomic force microscope image of Sb-based quantum dots (QDs) on a GaAs surface.