Large phase modulation of THz wave via an enhanced resonant active HEMT metasurface

Yaxin Zhang,Tianchi Zhou,Pinaki Mazumder,Shixiong Liang,Ziqiang Yang,Hongxin Zeng,Lan Wang,Wei Kou,Qin Chen,Jiaguang Han,Bo Zhang,Yuncheng Zhao,Feng Lan,Zhihong Feng

doi:10.1515/nanoph-2018-0116

Abstract

Abstract Terahertz (THz) science and technology promise unique applications in high-speed communications, high-accuracy imaging, and so on. To keep up with the demand for THz systems, THz dynamic devices should feature large phase shift modulation and high speed. To date, however, only a few devices can efficiently manipulate the phase of THz waves. In this paper, we demonstrate that efficient phase modulation of THz waves can be addressed by an active and enhanced resonant metamaterial embedded with a nanostructured 2D electron gas (2DEG) layer of a GaN high electron mobility transistor (HEMT). The enhanced resonant metaunit couples the traditional dipolar and inductance-capacitance resonances together to realize a coupling mode with enhanced resonance. Embedded with the nanostructured 2DEG layer of GaN HEMT, the resonance intensity and surface current circuit of the enhanced resonant mode in the metamaterial unit can be dynamically manipulated by the electrical control of the carrier distribution and depletion of the 3 nm 2DEG, leading to a phase shift greater than 150° in simulation. In the dynamic experiments, a 137° phase shift was achieved with an external controlling voltage of only several volts in the THz transmission mode. This work represents the first realization of a phase shift greater than 100° in a dynamic experiment in transmission mode using an active metamaterial structure with only a single layer. In addition, given the high-speed modulation ability of the HEMT, this concept provides a promising approach for the development of a fast and effective phase modulator in THz application systems.

Highlights

As a notable and attractive area of scientific research, the field of terahertz (THz) science and technology has developed rapidly in the past decades
Zhang et al.: Large phase modulation of THz wave via an enhanced resonant active high electron mobility transistors (HEMTs) metasurface to realize amplitude modulation of THz waves [12], intense effort has been devoted in the area of active THz metamaterials to develop ultrafast THz dynamic devices [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]
The heterostructure of GaN HEMT consists of a 25-nm-thick Al0.27Ga0.73N barrier layer, a 1 μm undoped GaN layer, and a 1.5 μm GaN buffer layer

Summary

Introduction

As a notable and attractive area of scientific research, the field of terahertz (THz) science and technology has developed rapidly in the past decades. The integration of doped silicon [13,14,15], GaAs semiconductor material [16], high electron mobility transistors (HEMTs) [17], VO2 phase transition material [18,19,20,21], and graphene with metamaterials [22,23,24,25,26,27,28,29,30,31,32,33] has been applied to enable the optical and electrical control of THz wave transmission Most of these previous works focused on the amplitude modulation of THz waves to develop THz switches, THz modulators for on-off keying communication, and wavefront-coding imaging devices, whereas relatively few researchers have attempted to achieve THz phase modulation using semiconductor-metamaterial structures [16, 34,35,36,37].

Device design and fabrication

A nalysis of the relation between phase jump change and resonance

Analysis of dynamic mode conversion controlled by the 2DEG nanostructure

Analysis of dynamic experiment

Conclusion