Modal Analysis of β−Ga2O3:Cr Widely Tunable Luminescent Optical Microcavities

Abstract

Optical microcavities are key elements in many photonic devices, and those based on distributed Bragg reflectors (DBRs) enhance dramatically the end reflectivity, allowing for higher quality factors and finesse values. Besides, they allow for wide wavelength tunability, needed for nano-and microscale light sources to be used as photonic building blocks in the micro-and nanoscale. Understanding the complete behavior of light within the cavity is essential to obtaining an optimized design of properties and optical tunability. In this work, focused ion-beam fabrication of high refractive-index contrast DBR-based optical cavities within Ga 2 O 3 ∶Cr microwires grown and doped by the vapor-solid mechanism is reported. Room-temperature microphotoluminescence spectra show strong modulations from about 650 nm up to beyond 800 nm due to the microcavity resonance modes. Selectivity of the peak wavelength is achieved for two different cavities, demonstrating the tunability of this kind of optical system. Analysis of the confined modes is carried out by an analytical approximation and by finite-difference-time-domain simulations. A good agreement is obtained between the reflectivity values of the DBRs calculated from the experimental resonance spectra, and those obtained by finite-difference-time-domain simulations. Experimental reflectivities up to 70% are observed in the studied wavelength range and cavities, and simulations demonstrate that reflectivities up to about 90% could be reached. Therefore, Ga 2 O 3 ∶Cr high-reflectivity optical microcavities are shown as good candidates for single-material-based, widely tunable light emitters for micro-and nanodevices.

Origin of Red Emission in β‐Ga2O3 Analyzed by Cathodoluminescence and Photoluminescence Spectroscopy

“…The origin of the red emission is quite ambiguous, and the literature provides three plausible explanations involving doping by transition metals or rare earth metals [ 10–14,19–21 ] or by nitrogen. [ 22,23 ] Figure 1b shows the CL spectra recorded in the region of 700 nm to provide more details in the near‐IR region of the spectrum.…”

“…The optical properties of β ‐ Ga 2 O 3 grown by various methods with different dopants have been widely reported, [ 5–9 ] primarily for emission in the UV and blue regions of the visible spectrum. However, there are only a few reports [ 10–14 ] on emission in the red spectral region due to transition metals, which is the focus of this work. We discuss red emission in relation to various dopants in β‐Ga 2 O 3 .…”

Exciting and confining light in Cr doped gallium oxide

“…Before patterning, luminescence spectra due to excitation with the UV laser (λ exc = 325 nm) are detected locally from one end of the structure of interest. After patterning, detection is performed on a different point to excitation, as explained elsewhere 9,10 . Figure 2(a) shows the room-temperature μ-PL image from cavity 2B in these conditions.…”

“…This oxide combines a very high breakdown field with a wide tunable PL range, spanning from the UV to the IR depending on the dopant used 5,6 . We have studied waveguiding and confinement on Cr doped Ga 2 O 3 microwires in the past decade [7][8][9][10] . In addition to the phonon-assisted red-NIR broad band and the R-lines 7 , low quality modulations due Fabry-Perot reflections in the wire ends were demonstrated 9 .…”

“…In addition to the phonon-assisted red-NIR broad band and the R-lines 7 , low quality modulations due Fabry-Perot reflections in the wire ends were demonstrated 9 . With the objective of improving their reflectivity and tuning their resonances in the broad red-NIR range, DBR-based Ga 2 O 3 :Cr optical microcavities have been very recently developed and their resonant modes have been thoroughly studied 10 . These microcavities dramatically enhance their optical performance in comparison to the unpatterned microwires.…”