Abstract
We characterise THz output of lateral photo-Dember (LPD) emitters based on semi-insulating (SI), unannealed and annealed low temperature grown (LTG) GaAs. Saturation of THz pulse power with optical fluence is observed, with unannealed LTG GaAs showing highest saturation fluence at 1.1 ± 0.1 mJ cm(-2). SI-GaAs LPD emitters show a flip in signal polarity with optical fluence that is attributed to THz emission from the metal-semiconductor contact. Variation in optical polarisation affects THz pulse power that is attributed to a local optical excitation near the metal contact.
Highlights
Terahertz emission from the photo-Dember (PD) effect arises from the differing mobilities of holes and electrons within a semiconductor [1]
The lateral photo-Dember (LPD) emitter based on unannealed low temperature grown (LTG) GaAs demonstrates a linear relationship between output THz power
As the number of trap states in unannealed LTG GaAs are of the order of 5 × 1019 cm−2 they are greater than the number of carriers generated [24]
Summary
Terahertz emission from the photo-Dember (PD) effect arises from the differing mobilities of holes and electrons within a semiconductor [1]. In the lateral photo-Dember (LPD) effect a radiative terahertz dipole is created by partially masking the semiconductor surface with a metal layer. By focussing an ultrafast laser, with above band-gap energy, on the metal-semiconductor boundary a spatially asymmetrical distribution of carriers forms near the metal-semiconductor interface [9,10] Such a device gives intense THz emission as observed by [10,11,12,13,14]. Optical polarisation affects LPD emitter performance, with peak THz emission occurring at perpendicular polarisation relative to the semiconductor-metal boundary. This polarisation dependency has similar behaviour to that observed in photoconductive antennas [21]. We explain the polarisation dependency with a finite element simulation of the electric field of the optical pulse for different polarisations under the LPD metal mask
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