Investigation of the role of the lateral photo-Dember effect in the generation of terahertz radiation using a metallic mask on a semiconductor

Abstract

Pulses of coherent terahertz radiation can be efficiently generated by a lateral diffusion current after ultrafast generation of photo-carriers near a metal interface on the surface of a semiconductor, this is known as the lateral photo-Dember effect. We investigate how the emission depends on the pump spot position, size, power and how it is affected by the application of an applied external bias. We study the role of the metallic mask and how it suppresses emission from the carriers diffusing under it due to a reduction of available radiation states both theoretically and experimentally.

Terahertz Focusing and Polarization Control in Large-Area Bias-Free Semiconductor Emitters

“…This is attributed to the device emitting both from photoDember currents and the intrinsic net lateral current due to the Schottky effects. The emission asymmetry with angle is due to the asymmetric nature of LPD emission in general [18] and the asymmetrical geometry of the DM emitter element. A circular Fig.…”

“…This paper explores beam steering using large-area emitters that generate THz radiation via diffusion currents, also known as the lateral photo-Dember (LPD) effect [17][18][19] and Schottky potentials [20,21]. LPD and Schottky potential-based double metallic emitters have been found to have similar spectral bandwidth with photo-conductive emitters [19,20] .…”

Generation of radially-polarized terahertz pulses for coupling into coaxial waveguides

“…However the ionization process also requires high-power amplified ultra-short laser pulses and the generated THz field in both schemes exhibits a conical wavefront. Recently, it was demonstrated that transient photo-currents excited on semiconductor surfaces by short (100 fs) optical pulses can have a large radial component due to the photo-generated charge density gradients20212223 and anisotropic conductivity24. This mechanism can provide efficiency, simplicity and tunability (i.e., dynamic control) in generation of THz beams with a tailored polarization state (e.g., radially-polarized THz beam) since the polarization state is governed by the shape of the optical beam and does not require bias.…”

Near-Field Analysis of Terahertz Pulse Generation From Photo-Excited Charge Density Gradients

“…More recently, photo-currents within the plane of the semiconductor surface were harnessed as a process for THz pulse generation [13][14][15][16][17][18]. Using normal incidence optical excitation, significant emission was observed in systems with an asymmetric photoexcited charge density distribution across the surface formed at the edge of a metallic contact [13,14].…”

“…13 and 15 suggest that the metal layer is not required if a high gradient is present, whereas Refs. [16][17][18] suggest that the metal layer is crucial for emission. This has raised questions over the distribution of photo-current responsible for the lateral photo-Dember effect.…”