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

TL;DR

This study investigates how the directionality of terahertz waves emitted from groove-patterned InAs structures depends on structural parameters and epilayer thickness, revealing mechanisms and enhancing emission through pattern design.

Contribution

It provides new insights into the emission mechanisms based on thickness and demonstrates how groove patterns can enhance THz emission directionality.

Findings

Carrier drift dominates in thin InAs layers (10-70 nm).

Electronic diffusion overrides drift in thick layers (370-900 nm).

Groove patterns enhance THz amplitude along specific directions.

Abstract

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.