Advances in Engineering Advances in Engineering features breaking research judged by Advances in Engineering advisory team to be of key importance in the Engineering field. Papers are selected from over 10,000 published each week from most peer reviewed journals.
Optics Express, Vol. 21, Issue 17, pp. 19709-19717 (2013).
Jong-Hyuk Yim, Hoonil Jeong, Muhammad Irfan, Eun-Hye Lee, Jin-Dong Song, and Young-Dahl Jho.
School of Info. and Comm., Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea and
Center for Opto-Electronics Convergence Systems, Korea Institute of Science and Technology, Seoul 136-791, South Korea
Abstract
The terahertz (THz) radiation from transient dipoles, formed by distinct diffusion coefficients between oppositely charged carriers as often observed in low band gap semiconductors, propagates with an anisotropic amplitude distribution perpendicular to the dipole axis along the diffusive motion. By directionally adjusting the electronic diffusion, we conceptualize groove-patterned THz emitters based on (100) InAs thin films and demonstrate the unidirectional radiation. Line-of-sight emission along the surface-normal direction is greatly enhanced in a distributed asymmetric trapezoid with its period similar to the electronic diffusion length of InAs. This directional enhancement is in clear contrast to the constant emission amplitude along the lateral direction, regardless of pattern scale, which manifests the role of groove patterns as microscale reflectors in laterally corrugating the carrier density. In contrast to the rather limited nonlinearity in (100) plane, the azimuthal angle dependence of the THz field amplitude in corrugated samples shows a combined effect of diffusive transport and second-order nonlinearity, whose compositional contributions varies in different structures.
© 2013 OSA
