| Title: | Oddziaływanie kulombowskie w układach dwuwarstwowych 2D: w kierunku niestabilności dwustrumieniowej dla emisji THz |
| Project leader: | Adil Rehman |
| Laboratory: | Crystal Growth Laboratory (NL-3) |
| Project number: | 2024/08/X/ST7/01333 |
| Implementation date: | 09.12.2024 08.12.2025 |
| Total funding granted: | 49 999 zł |
| Funding for the entity: | 49 999 zł |
Project description
| Introduction The project aims to investigate the Coulomb charge carrier's interaction (CCI) in graphene-graphene and graphene-AlGaN/GaN-based systems via DC and noise measurements. Special focus will be given to the strong Coulomb interaction with negligible carriers tunneling. The investigation and understanding of the CCI in a double-layer two-dimensional (2D) system separated by a thin dielectric layer will pave the way for innovative terahertz (THz) radiation sources. The outcome of the investigation will be used as preliminary results for future project, where an innovative design for THz devices will be proposed based on the interaction of charge carriers in bilayer systems consisting of two independent 2D layers. Motivation and Background The bilayer systems consisting of two independent 2D layers of charge carriers in close proximity provide a fascinating platform to verify the theoretical prediction of electronic Kelvin–Helmholtz instability, which can be used to design innovative THz devices. The atomically thin nature of graphene enables the creation of such structures. Moreover, ultrahigh mobility and ambipolar transport properties make graphene an ideal system for such investigation. Likewise, AlGaN/GaN exhibits high electron mobility and can be used to explore CCI. One of the important phenomena in two closely spaced 2D electron systems is the Coulomb interaction between charge carriers in these two layers. Particularly, a net momentum is transferred in the drag layer (or passive layer) due to the current flowing in the driven layer (active layer). When current is passed in different directions in these layers, high-frequency instability should emerge. Our preliminary measurement results on a double-layer 2D system consisting of AlGaN/GaN and graphene (grown via chemical vapor deposition (CVD) method) revealed the Coulombic CCI among two layers. Although the interaction was weak, the interlayer CCI can be enhanced by switching to the high-mobile exfoliated graphene sample and reducing the distance between layers. This Coulomb interaction between closely spaced conducting layers should induce turbulence and oscillations, and such phenomena could be used for the generation of THz radiations. Objectives • Study the Coulomb interaction by DC and noise measurements in double-layer 2D systems consisting of graphene and AlGaN/GaN heterostructures. • Enhance the CCI by using a high-mobile graphene flake and a thin dielectric layer. • Establish the best technological and electrical conditions for the enhancement of interactions between the two 2D systems. • Search for optimal designs to induce two-stream instability in double-layer 2D systems for generating electromagnetic radiation in the THz frequency band. Methodology • High-mobile graphene and AlGaN/GaN-based double-layer 2D systems will be designed and fabricated. • Independent contacts will be fabricated to individual layers for detailed characterization. • Comprehensive DC and noise measurements will be performed to evaluate the quality of the fabricated devices and understand the physics of Coulomb interaction. • The measured data will be analyzed, and the best possible sample will be chosen for a preliminary experiment. Hypothesis • The high mobility of graphene enhances the interlayer CCI in a closely spaced double-layer 2D system. • DC and noise measurements provide insight of interlayer interaction. • A closely spaced double-layer 2D system can be a choice for THz generation. Expected Outcomes • Optimal device configuration will be chosen to investigate the two-stream instability. • The best possible technological and experimental conditions will be established to perform the preliminary experiment for THz emission. Significance of the Project The project will provide insights of CCI dynamics in a double-layer 2D system and will establish a solid pillar for the development of a new class of THz devices based on Kelvin–Helmholtz's two-stream instability in two interacting electronic systems. Connection Between Current Research Activity with Future Project Call: Rationale and Scientific Impact The terahertz (THz) radiations lie between microwave and far-infrared-regime of the electromagnetic spectrum. Initially, the THz frequency band (ranging from 0.1 to 10 THz) was used only for astronomy or spectroscopic studies but later on, it was realized that the THz band has remarkable potential for different applications. However, it suffers from the lack of cost-effective large-scale integrable semiconductor devices [1]. While quantum cascade lasers cover the frequency above 2 THz and semiconductor sources with multipliers hardly reach 1 THz from the low frequency side, the frequency band around 1-2 THz remains the more challenging. One of the approaches to this frequency band is based on semiconductor plasmonics. Dyakonov and Shur (D-S) proposed that plasmons in two-dimensional electron gas (2DEG) in field effect transistors (FETs) can be unstable and such instability can be used for the generation of electromagnetic radiation in the THz frequency band. However, the experimental results based on D-S theory achieved only broadband THz emissions in the nanowatt power range (impractical for real-world applications). In the near future project call, we will study another type of plasmon instability, where a bilayer system consisting of two independent two-dimensional (2D) layers of charge carriers in close proximity will be proposed for the design of innovative THz emitters. The working principle of such emitters will be based on the theoretical prediction of electronic Kelvin–Helmholtz instability. According to this theory, the relative motion of charge carriers in two layers separated by a thin dielectric layer with different velocities causes a force at the interface, which leads to the disturbance and growth of oscillations (analogous to the wave formation on a water surface due to the wind) [2, 3]. |