Design, fabrication, and optical characteristics of freestanding GaN waveguides on silicon substrate

Takuji Sekiya, Takashi Sasaki, Kazuhiro Hane

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22 Citations (Scopus)


Freestanding GaN waveguides were fabricated on a silicon substrate by a combination of Cl2 plasma reactive ion etching and XeF2 gas selective etching. The freestanding GaN waveguides ranged from 0.23 to 8 μm in width and were supported in air by bridge structures. The bridge structures were designed via rigorous electromagnetic simulations using the finite-difference time-domain method. The GaN layer was grown epitaxially on a silicon (111) substrate using a buffer layer to compensate for the crystal lattice constant mismatch. Using two types of masks, the GaN layer was etched using a Cl2 inductively coupled plasma. The 625-nm-thick GaN layer was etched by the Cl2 plasma at a substrate temperature of -17 °C to form the GaN waveguide patterns, at the expense of a 92-nm-thick HfO2 mask layer. The etching rate of the GaN layer was 170 nm/min and the etching ratio between the GaN and HfO2 layers was 6.8:1. The silicon substrate was then isotropically etched using XeF2 gas to generate air gaps underneath the GaN waveguides. The transmittance of the fabricated freestanding GaN waveguides was measured using a visible (406 nm) laser and an infrared (1550 nm) laser. The waveguide losses for a 730-nm-wide and 625-nm-thick waveguide were 2.6 dB/mm at 406 nm and 2.2 dB/mm at 1550 nm. These results indicate that the structures are likely to be useful for several visible waveguide devices combined with blue GaN light emitting diodes and for optical telecommunication waveguide devices using the wide transmission window of the GaN crystal.

Original languageEnglish
Article number031207
JournalJournal of Vacuum Science and Technology B: Nanotechnology and Microelectronics
Issue number3
Publication statusPublished - 2015 May 1

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Instrumentation
  • Process Chemistry and Technology
  • Surfaces, Coatings and Films
  • Electrical and Electronic Engineering
  • Materials Chemistry


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