Rare-earth materials epitaxially codeposited with III-V semiconductors form small, spherical rare-earthmonopnictide nanoparticles embedded within the III-V host. The small size of these particles (approximately 1.5 nm diameter) suggests that interesting electronic properties might emerge as a result of both confinement and surface states. However, ErAs nanoparticles do not exhibit any signs of quantum confinement or an emergent band gap, and these experimental observations are understood theoretically. We use ultrafast pump-probe spectroscopy to investigate the electronic structure of TbAs nanoparticles embedded in a GaAs host, which were expected to be similar to ErAs. We study the dynamics of carrier relaxation into the TbAs states, which essentially act as traps, using optical-pump terahertz-probe transient absorption spectroscopy. By analyzing how the carrier relaxation rates depend on pump fluence and sample temperature, we conclude that the TbAs states are saturable. Saturable traps suggest the existence of a band gap for TbAs nanoparticles, in sharp contrast with the results for ErAs.
The incorporation of lanthanide pnictide nanoparticles and films into III-V matrices allows for semiconductor composites with a wide range of potential optical, electrical, and thermal properties, making them useful for applications in thermoelectrics, tunnel junctions, phototconductive switches, and as contact layers. The similarities in crystal structures and lattice constants allow them to be epitaxially incorporated into III-V semiconductors with low defect densities and high overall film quality. A variety of growth techniques for these composites with be discussed, along with their growth mechanisms and current applications, with a focus on more recent developments. Results obtained from molecular beam epitaxy film growth will be highlighted, although other growth techniques will be mentioned. Optical and electronic characterization along with the microscopy analysis of these composites is presented to demonstrate influence of nanoinclusion composition and morphology on the resulting properties of the composite material.
We propose and systematically justify a band structure for TbAs nanoparticles in GaAs and In0.53Ga0.47As host matrices. Fluence-dependent optical-pump terahertz-probe measurements suggest the TbAs nanoparticles have a band gap and provide information on the carrier dynamics, which are determined by the band alignment. Spectrophotometry measurements provide the energy of optical transitions in the nanocomposite systems and reveal a large blue shift in the absorption energy when the host matrix is changed from In0.53Ga0.47As to GaAs. Finally, Hall data provides the approximate Fermi level in each system. From this data, we deduce that the TbAs:GaAs system forms a type I (straddling) heterojunction and the TbAs:In0.53Ga0.47As system forms a type II (staggered) heterojunction.
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