  We have performed terahertz (THz)-time domain spectroscopy in various
geometries, for characterizing the directivity of THz waves emitted from
groove-patterned InAs structures. First, we have distinguished the THz emission
mechanisms as a function of epilayer thickness. The carrier drift was
predominant in thin sample group (10-70 nm) which the electronic diffusion
motion was overriding the oppositely aligned drifting dipoles in thick sample
group (370-900 nm) as revealed via amplitude and phase variations. By combined
use of the electron-beam lithography and the inductively coupled plasma etching
in 1 {\mu}m-thick InAs epilayers, we have further fabricated either asymmetric
V-groove patterns or symmetric parabolic patterns. The THz amplitude was
enhanced, particularly along line-of-sight transmissive direction when the
groove patterns act as microscale reflective mirrors periodically separated by
a scale of diffusion length.
