Nexus between directionality of terahertz waves and structural parameters in groove patterned InAs

Abstract

We performed terahertz (THz) time-domain spectroscopy in various geometries, for characterizing the directivity of THz waves emitted from groove patterned InAs structures. We first identified two transient transport processes as underlying THz emission mechanisms in InAs epilayers with different thicknesses. Carrier drift around the surface depletion region was predominant for the THz wave generation in the thin sample group (10–70 nm), whereas electronic diffusion overrode the drift currents in the thick sample group (370–900 nm) as revealed by the amplitude change and phase reversal. Through a combination of electron-beam lithography and inductively coupled plasma etching in 1 μm-thick InAs epilayers, we could further periodically fabricate either asymmetric V-groove patterns or symmetric parabolic apertures. The THz amplitude was enhanced, particularly along the line-of-sight transmissive direction when the periodic groove patterns act as microscale reflective mirrors separated by a scale of the diffusion length.