Abstract
Plasmonic internal photoemission detectors (PIPED) have recently been shown to combine compact footprint and high bandwidth with monolithic co-integration into silicon photonic circuits, thereby opening an attractive route towards optoelectronic generation and detection of waveforms in the sub-THz and THz frequency range, so-called T-waves. In this paper, we further expand the PIPED concept by introducing a metal-oxide-semiconductor (MOS) interface with an additional gate electrode that allows to control the carrier dynamics in the device and the degree of internal photoemission at the metal-semiconductor interfaces. We experimentally study the behavior of dedicated field-effect (FE-)PIPED test structures and develop a physical understanding of the underlying principles. We find that the THz down-conversion efficiency of FE-PIPED can be significantly increased when applying a gate potential. Building upon the improved understanding of the device physics, we further perform simulations and show that the gate field increases the carrier density in the conductive channel below the gate oxide to the extent that the device dynamics are determined by ultra-fast dielectric relaxation rather than by the carrier transit time. In this regime, the bandwidth can be increased to more than 1 THz. We believe that our experiments open a new path towards understanding the principles of internal photoemission in plasmonic structures, leading to PIPED-based optoelectronic signal processing systems with unprecedented bandwidth and efficiency.
Highlights
Optoelectronic signal processing techniques offer great potential for generation and detection of waveforms in the sub-THz and THz frequency range, so-called T-waves [1,2,3,4], which may be key to ultra-broadband wireless communications in future sixth-generation (6G) networks [5,6]
We experimentally demonstrate the concept and verify the underlying principles using dedicated test devices with core widths of 175 nm, and we find that the sensitivity of these devices can be effectively tuned through the gate potential
We further show that the gate voltage increases the sensitivity slope, which determines the down-conversion efficiency for coherent T-wave detection
Summary
Optoelectronic signal processing techniques offer great potential for generation and detection of waveforms in the sub-THz and THz frequency range, so-called T-waves [1,2,3,4], which may be key to ultra-broadband wireless communications in future sixth-generation (6G) networks [5,6]. While the fundamental advantages of plasmonic internal photoemission detectors (PIPED) have been experimentally shown [3,7], the underlying operating principles are still subject to discussion One of these questions concerns the relative contributions of photo-emitted electrons and holes to the overall current, which is a key aspect to improve the device performance and to quantify the associated fundamental physical limitations for conversion efficiency and bandwidth. Building upon the improved understanding of the device physics, we further perform simulations showing that the carrier density in a thin channel below the gate can be increased to the extent that the dynamic device response is determined by ultra-fast dielectric relaxation rather than by the carrier transit time These simulations predict that the bandwidth of the device can be increased beyond 1 THz by applying a gate voltage.
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