Abstract
III-nitride surface states are expected to impact high surface-to-volume ratio devices, such as nano- and micro-wire light-emitting diodes, transistors, and photonic integrated circuits. In this work, reversible photoinduced oxygen desorption from III-nitride microdisk resonator surfaces is shown to increase optical attenuation of whispering gallery modes by 100 cm−1 at λ = 450 nm. Comparison of photoinduced oxygen desorption in unintentionally and n+-doped microdisks suggests that the spectral changes originate from the unpinning of the surface Fermi level, likely taking place at etched nonpolar III-nitride sidewalls. An oxygen-rich surface prepared by thermal annealing results in a broadband Q improvement to state-of-the-art values exceeding 1 × 104 at 2.6 eV. Such findings emphasize the importance of optically active surface states and their passivation for future nanoscale III-nitride optoelectronic and photonic devices.
Highlights
The proliferation of III-nitride semiconductor optoelectronics for solid-state lighting has encouraged research and development of small length scale devices for new applications
Comparison of photoinduced oxygen desorption in unintentionally and nþ-doped microdisks suggests that the spectral changes originate from the unpinning of the surface Fermi level, likely taking place at etched nonpolar III-nitride sidewalls
One could argue that the losses are due to quantum well (QW) absorption which could be modified during thermal processing, the annealing temperature remains below the 880 C threshold expected to alter InGaN/GaN QWs
Summary
The proliferation of III-nitride semiconductor optoelectronics for solid-state lighting has encouraged research and development of small length scale devices for new applications. Examples include nanowire light-emitting diodes (LEDs) for lighting and nanolasers, high frequency transistors for power electronics, and nanophotonics for photonic integrated circuits.. Examples include nanowire light-emitting diodes (LEDs) for lighting and nanolasers, high frequency transistors for power electronics, and nanophotonics for photonic integrated circuits.5 These additional application opportunities for small devices are paid at the expense of an increased surface-to-volume ratio. Past research on GaN-based nanophotonic structures has identified several candidate loss channels that may limit experimental Q at high energies or short wavelengths (2.5–3 eV/400–500 nm). Such issues may apply to recent AlN-based photonic devices designed for the UV.. Such issues may apply to recent AlN-based photonic devices designed for the UV. In GaN, Puchtler et al advocated a correlation between the dislocation defect density and experimental Q.21 Other authors proposed residual absorption in bulk GaN22 and/or surface roughness at short wavelengths as the main responsible mechanism. We recently quantified losses in GaN photonic nanostructures and showed that the dominant loss mechanism is linked to the III-nitride semiconductor surface. This work examines the impact of optically active surface states on whispering gallery resonances in III-nitride microdisks via reversible photoinduced oxygen desorption from the GaN surface
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