Correlation between the optical loss and crystalline quality in erbium-doped GaN optical waveguides

Abstract

Erbium-doped GaN (GaN:Er) epilayers were synthesized by metal organic chemical vapor deposition. GaN:Er waveguides were fabricated based on four different GaN:Er layer structures: GaN:Er/GaN/Al2O3, GaN:Er/GaN/AlN/Al2O3, GaN:Er/GaN/Al(0.75)Ga(0.25)N/AlN/Al2O3, and GaN/GaN:Er/GaN/Al2O3. Optical loss at 1.54 μm in these waveguide structures has been measured. It was found that the optical attenuation coefficient of the GaN:Er waveguide increases almost linearly with the GaN (002) x-ray rocking curve linewidth. The lowest measured loss was ~6 dB/cm.

Excitation cross section of erbium-doped GaN waveguides under 980 nm optical pumping

“…Linear relation was found between optical attenuation coefficient of Er:GaN waveguide and the x-ray rocking curve linewidth of the GaN crystal. 13 In this Letter, we show that spontaneous emission carrier lifetime is inversely proportional to the x-ray rocking curve linewidth. In addition, we show that the excitation cross section of Er:GaN at 980 nm wavelength is approximately 2:2 Â 10 À21 cm 2 , which is relatively independent of the Er:GaN crystalline quality.…”

“…It has also been found that the optical attenuations of waveguides depend on the quality of the GaN crystalline quality characterized by the FWHM of XRD rocking curves. 13 Higher optical loss was found to be associated with broader XRD rocking curves. In general, optical loss in a waveguide can be attributed to both scattering and absorption of optical signal.…”

“…Three Er:GaN waveguides with a similar Er concentration of approximately 2 Â 10 20 cm À3 (Ref. 13) were used in this study with their layer structures shown in the inset of Fig. 1.…”

“…This crystalline quality can be quantified by an x-ray diffraction (XRD) measurement. The full-width at half maximum (FWHM) of XRD rocking curves of (002) peak (x-scan) are 430, 530, and 650 arc-seconds, respectively, for samples A, B, and C. 13 As a comparison, the undoped GaN epilayers grown on sapphire synthesized with the same MOCVD system typically have a FWHM of approximately 360 arc sec for (002) racking curve. The quantitative measure of crystalline quality allows the investigation of its impact in other parameters of Er:GaN waveguides.…”

Lanthanides and actinides: Annual survey of their organometallic chemistry covering the year 2013

“…GaN Optical loss at 1.54 m in these waveguide structures has been measured. It was found that the optical attenuation coefficient of the GaN:Er waveguide increases almost linearly with the GaN (0 0 2) X-ray rocking curve linewidth [145]. In a closely related study, epilayers of erbium-doped GaN (GaN:Er) were synthesized by MOCVD using tris(cyclopentadienyl)erbium precursors, and the optical excitation cross section ( exc ) of the Er ions in this host material were determined.…”