Design and analysis of electro-optic modulators based on high contrast gratings in AlGaN/GaN heterostructures

Abstract

Recently High Electron Mobility Transistor (HEMT) inspired III-V electro-optic modulator topologies were proposed for realizing high speed electro-optic modulators leveraging plasma dispersion effect due to the 2D Electron Gas (2DEG) present at the III-V heterostructure interface. The 2DEG is highly confined at the interface, extending to very low depths in the bulk (≈10 nm) and therefore has limited spatial overlap with the optical mode. In this paper, we propose a novel modulator design to boost the 2DEG-light interaction, wherein the HEMT is embedded within a high contrast grating (HCG) mirror. We present an analytical model extending the conventional HCG model to multi-layer structures and observe good agreement with rigorous coupled-wave analysis (RCWA). We explore the design space for identifying optimal device topology and present geometries that produce a change in reflectivity as large as 70 % for C-and L-band wavelengths. We also present results of sensitivity analysis and observe low variation in device performance due to geometry variation arising from device fabrication imperfections. The device platforms presented here are suitable for designing high efficiency electro-optic modulators by incorporating the HEMT HCG into a Fabry-Perot cavity.

High‐Electron‐Mobility Transistor‐Inspired Freestanding AlGaN/GaN/AlN Optical Waveguide for High‐Pressure Sensing Applications

“…Even the 2DEG layer is highly localized to improve the modulation efficiency significantly but when compared to their previous work, not that much improvement is observed. [ 15 ] To exploit properties of embedded GaN layer, the researchers used freestanding GaN to achieve high emission efficiency, and all pass transmission by removing the substrate while eliminating the side‐lobe reflectivity. Unlike traditional multilayer dielectric film layers, freestanding structures are more compact, and the lattice mismatch between the GaN and substrate layers can be minimized.…”

“…[11] On the other side, photonic integrated circuits are thriving with the help of III-nitride-based semiconductor materials for numerous optical devices such as lasers, modulators, couplers, sensors, and detectors. [12][13][14][15] Group III-nitride materials enabled development of a single chip with all the optical devices integrated and connected using inbuilt optical interconnects. [16] The reasons to explore GaN/AlN/AlGaN are wide transparency window (UV-IR), high birefringence, high nonlinear coefficient, and low thermo-optic coefficient.…”

“…Even the 2DEG layer is highly localized to improve the modulation efficiency significantly but when compared to their previous work, not that much improvement is observed. [15] To exploit properties of embedded GaN layer, the researchers used freestanding GaN to achieve high emission efficiency, and all pass transmission by removing the substrate while eliminating the side-lobe reflectivity. Unlike traditional multilayer dielectric film layers, freestanding structures are more compact, and the lattice mismatch between the GaN and substrate layers can be DOI: 10.1002/pssa.202200637 Herein, a high-pressure sensor based on freestanding high-electron-mobility transistor (HEMT)-inspired optical waveguide comprising AlGaN/GaN/AlN layers on silicon carbide (SiC) substrate is proposed and studied for harsh environment applications using finite element method (FEM).…”

Dispersion engineering of GaN based coupled waveguides for blue frequency combs

“…GaN has emerged as a superior platform in various domains from high-power terahertz (THz) imaging and spectroscopy systems, monolithic microwave integrated circuits (MMICs), to nonlinear optics owing to its rich material properties such as wide band gap, high electron saturation velocity and high breakdown voltage, and wide band operation from UV to IR region [13,14]. This has spawned several device applications such as photo-diodes [15], lasers [16], electro-optical modulators [17] etc. With its proven technical prowess for highspeed and high-power applications, and emerging research in exploitation of electro-optic properties, coupled with ease of manufacturing [18][19][20], GaN based chip-scale photonic ICs are well poised to morph into a strong platform for optoelectronic monolithic integration.…”