Enhanced terahertz radiation of photoconductive antenna fabricated on GaAs-on-sapphire

Jitao Zhang,Michael Gehl,Mingguang Tuo,Ricky Gibson,Hao Xin,Min Liang

doi:10.1063/1.5127877

Abstract

The terahertz (THz) radiation properties of a photoconductive antenna (PCA) fabricated on a GaAs-on-sapphire (GoS) substrate are reported at sub-THz band. The GaAs layer with a thickness of approximately 1 µm was directly deposited on a sapphire wafer by means of molecular beam epitaxy. A butterfly-shaped antenna structure was then fabricated on the GoS substrate by photolithography, and the device was tested as the emitter of an in-house built THz time-domain spectrometer. The performance of this antenna was compared with a commercial one, which had an identical antenna structure but was fabricated on low-temperature-grown GaAs (LT-GaAs). The results showed that the GoS-based PCA radiated an enhanced THz field, which could be as much as 1.9 times that of the LT-GaAs-based PCA, indicating that GoS could be a promising photoconductive material. In addition, the optical transparency of the sapphire substrate allows the device to be illuminated from the backside, which is crucial for THz near-field imaging applications where the sample is usually in close proximity to the front surface of the PCA device.

Highlights

Since its appearance in the 1980s, photoconductive antennas (PCAs) have been widely used as pulsed terahertz (THz) sources.1–3 A PCA usually consists of a substrate, a metallic structure that is fabricated on top and an active layer in between
Along with the invention of the PCA, numerous materials have been demonstrated as the active layer, such as radiation-damaged silicon on sapphire (RD-SoS), InP, InGaAs, ion-implanted GaAs, semi-insulating GaAs, and low-temperature grown GaAs (LT-GaAs)
Regarding the applications where backside laser illumination is required,12,13 LT-GaAs substrates cannot be utilized because GaAs is opaque at the excitation laser wavelength

Summary

Introduction

Since its appearance in the 1980s, photoconductive antennas (PCAs) have been widely used as pulsed terahertz (THz) sources.1–3 A PCA usually consists of a substrate, a metallic structure that is fabricated on top and an active layer in between. The THz radiation properties of the PCA fabricated on this GaAs-on-sapphire (GoS) substrate were evaluated by THz time-domain spectroscopy (THz-TDS).

Results

Conclusion