Ultrafast sub-bandgap photo-response in ErAs/GaAs at 1550 nm

Erbium arsenide (ErAs) is a semi-metallic compound that can be epitaxially grown and integrated to III-V semiconductors such as GaAs and InGaAs, etc., to generate tunable optoelectronic properties, for example, the ultrafast photo-carrier lifetimes. [1] However, the wider bandgap of GaAs limits the application of ErAs/GaAs in 1550 nm. In this study, we present different ways to integrate ErAs and GaAs and utilize the absorption within the GaAs bandgap to realize ultrafast photo-response at 1550 nm. The infrared absorption and 1550 nm ultrafast photo-response in epitaxial ErAs/GaAs systems are studied by Fourier transform infrared (FTIR) spectroscopy and time-resolved pump-probe technique. The sub-bandgap absorption in ErAs/GaAs has been observed in all the samples and can be tuned by the ErAs incorporation. The ultrafast photo-induced carrier lifetime at 1550 nm is measured to be as low as 200 fs, and the relaxation mechanism is discussed in detail. This material system is promising for 1550-nm-technology-compatible THz sources with high breakdown-voltages.
[1] M. Griebel, J. H. Smet, D. C. Driscoll, J. Kuhl, C. A. Diez, N. Freytag, C. Kadow, A. C. Gossard, K. Von Klitzing, Nat. Mater. 2003, 2, 122.