Abstract
Utilising dislocation-related vertical etching channels in gallium nitride, we have previously demonstrated a simple electrochemical etching (ECE) process that can create layered porous GaN structures to form distributed Bragg reflectors for visible light at wafer scale. Here, we apply the same ECE process to realise AlGaN-based ultraviolet distributed Bragg reflectors (DBRs). These are of interest because they could provide a pathway to non-absorbing UV reflectors to enhance the performance of UV LEDs, which currently have extremely low efficiency. We have demonstrated porous AlGaN-based UV DBRs with a peak reflectance of 89% at 324 nm. The uniformity of these devices is currently low, as the as-grown material has a high density of V-pits and these alter the etching process. However, our results indicate that if the material growth is optimised, the ECE process will be useful for the fabrication of UV reflectors.
Highlights
Deep Ultraviolet (DUV) light is crucial for a wide range of industrial applications from curing processes to sterilisation
Al content emits light deep into the UV and AlGaN-based LEDs presenting a candidate for a UV light source, which could mitigate all of these disadvantages
There are frequent and large channels of porosity that pass through the non-intentionally doped doped (NID) layers, which disrupt the layer structure
Summary
Deep Ultraviolet (DUV) light is crucial for a wide range of industrial applications from curing processes to sterilisation. This light is predominantly produced by mercury (Hg) lamps, despite their limited lifetimes, use of high voltages, and the requirement for highly toxic Hg. AlGaN with a high. AlGaN optoelectronic devices operating in the DUV currently exhibit very low efficiency This is due to various factors that are associated with increasing aluminium content of the AlGaN material required to reach shorter wavelengths [2]. These problems are due to: low internal quantum efficiency due to high defect density [2]; high light absorption from p-GaN layers [3] necessary to provide effective hole injection; and, the strong anisotropic emission of AlGaN, which causes c-plane grown AlGaN to preferentially emit laterally [4]
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