Low-Loss Buried-Heterostructure Optical Waveguide Based on Impurity-Free-Vacancy-Diffusion Quantum Well Intermixing

Cong-Long Chen,Yu-Hung Lin,Rih-You Chen,Yang-Jeng Chen,Chih-Hsien Chen,Po-Yun Wang,Yen-Hsiang Chang,Yi-Jen Chiu

doi:10.1109/jphot.2020.2978401

Cong-Long Chen, Yu-Hung Lin + Show 6 more

Open Access

https://doi.org/10.1109/jphot.2020.2978401

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Journal: IEEE Photonics Journal	Publication Date: Apr 1, 2020
Citations: 9	License type: CC BY 4.0

Affiliation: National Sun Yat-sen University

Abstract

A new method for fabricating a high-quality buried-heterostructure optical waveguide using quantum well intermixing (QWI) has been demonstrated. By patterning a SiO2 thin film on top of a multiple quantum well (MQW) heterostructure, rapid thermal annealing (RTA) could induce laterally local QWI, resulting in a bandgap blueshift and a simultaneous decrease in the refractive index. Both lateral bandgap and index engineering could be attained along the MQW plane, which could be used for a buried-heterostructure optical waveguide. Two SiO2 strips with 3, 5 and 7 μm windows were fabricated for waveguide on a 1540 nm InGaAsP MQW sample. A 120 nm blueshift under the SiO2 area was observed, leading to the index contrast of 0.07. Far-field optical diffraction measurements were also performed to yield angles of 13.9°, 12.8° and 10.6°. A narrower window resulted in a narrower optical waveguide width and exhibited a larger diffraction angle, suggesting that QWI defined the buried optical waveguide. In addition, an electroabsorption modulator was also made by buried waveguide. A −10 dB low optical insertion loss and a 15 dB high extinction ratio in a 500 μm long waveguide were obtained, indicating that a buried heterostructure could be used for photonic devices and integration applications.

Highlights

Optical waveguide technology that uses III–V semiconductor materials plays an important role in photonic integrated circuits because the integrated performance of the devices or modules relies primarily on the waveguide properties
By defining the open window of the SiO2 capping layer on top of the material, the buried waveguide structure could be set after the quantum well intermixing (QWI) intermixing, where the open window defined the area of the optical waveguide, i.e., after the QWI of the refractive index under the SiO2 capping layer reduced from the blueshift of the bandgap
We demonstrated a novel method for fabricating a low loss buried-heterostructure waveguide by impurity free vacancy disorder (IFVD) QWI

Summary

Introduction

Optical waveguide technology that uses III–V semiconductor materials plays an important role in photonic integrated circuits because the integrated performance of the devices or modules relies primarily on the waveguide properties. The material with a higher bandgap and lower refractive index will cover and fill the sidewalls of the waveguide after etching the active region, which will form the lateral and vertical heterostructure. This fabrication scheme has technological challenges, such as (1) the passivation to remove the defects or vacancies and (2) the smooth surface on the junctions between two cladding layers and the surrounding region of the patterned active region. By defining the open window of the SiO2 capping layer on top of the material, the buried waveguide structure could be set after the QWI intermixing, where the open window defined the area of the optical waveguide, i.e., after the QWI of the refractive index under the SiO2 capping layer reduced from the blueshift of the bandgap. Ti/Au was deposited to create a coplanar-waveguide (CPW) electrical wire to produce an electrical feed line

Optical Measurement and Waveguide Characterization

Conclusion