Optical characterization of InAs/GaInSb superlattices for long-wavelength photodetectors

Mikhail Patrashin ¹ Norihiko Sekine ¹ Kouichi Akahane ² Iwao Hosako ¹

¹Advanced ICT Research Institute, National Institute of Information and Communications Technology
²Photonic Network Research Laboratory, National Institute of Information and Communications Technology

We report on optical characterization of InAs/GaInSb superlattices, which were designed for long-wavelength, terahertz range photodetectors (SL bandgap <50 meV). The SL samples were grown by solid-source Molecular Beam Epitaxy on GaSb (100) substrates [1]. The SL optical absorption, dielectric function and sub-band structure are evaluated from the transmittance and reflectance spectra measured by FTIR and THz time-domain spectroscopy. Measured characteristics are analyzed by using the band structure and energy dispersion relations calculated with multiband k×p method and dielectric functions derived from the Drude-Lorentz oscillator model.

[1] M. Patrashin, I. Hosako, K. Akahane, "Type-II InAs/GaInSb superlattices for terahertz range photodetectors", Proc. SPIE Vol. 8188, 81880G (2011)

Measured absorption coefficient in 40-period InAs(38Å)/In_0.29Ga_0.71Sb(29Å) superlattice. Reststrahlen band <35meV indicates a region of photon energies where the absorption is dominated by the resonance interactions with crystal lattice (optical phonons) of the substrate and the superlattice.