Electrochemical etching of III-nitride-materials is a fast-developing research field. This method is used to selectively porosify or completely etch such materials and thereby opens up a new design space for both photonic and electronic devices. Here we will focus on complete lateral electrochemical etching for substrate removal to realise thin-film vertical-cavity surface-emitting lasers (VCSELs) and light emitting diodes (LEDs). Key challenges that will be addressed are how to achieve etched surfaces as smooth as the as-grown material and how to protect fully processed and highly doped device structures such as tunnel junctions, during substrate removal.
We will give an overview of state-of-the-art results and challenges to achieve high-performing III-nitride vertical-cavity surface-emitting lasers (VCSELs), with a particular focus on the requirements to push the emission wavelength into the ultraviolet (UV). Our method to simultaneously achieve high-reflectivity mirrors and good cavity length control by electrochemical etching enabled the world’s first UV-B VCSEL. The use of dielectric mirrors yielded lasers with a very temperature-stable emission wavelength thanks to the negative thermo-optic coefficient of the mirrors. We have used the same etch methodology to also lift-off fully processed LEDs from their growth substrate to improve the light extraction efficiency.
In recent years, there has been tremendous improvement in the performance of blue-emitting vertical-cavity surface-emitting lasers (VCSELs) and they are now on the cusp of commercialization. We will summarize state-of-the-art results and outline the main challenges in extending the emission wavelength into the ultraviolet (UV). Our method to simultaneously achieve high-reflectivity mirrors and good cavity length control by selective electrochemical etching has been essential to demonstrate the world’s first UV-B VCSEL. The use of dielectric mirrors, where one material has a negative thermo-optical coefficient, counteracts the inherent red-shift of the resonance wavelength, enabling a temperature-stable emission.
We will give an overview of the progress in ultraviolet-emitting vertical-cavity surface-emitting lasers (VCSELs) and their potential applications in areas such as disinfection and medical therapy. This includes our demonstration of the shortest wavelength VCSEL, emitting at 310 nm under optical pumping, and a detailed analysis of its filamentary lasing characteristics. The UVB-emitting AlGaN-based VCSEL was realized by substrate removal using electrochemical etching, enabling the use of two high-reflectivity dielectric distributed Bragg reflectors. The potential of using this or alternative methods to push the emission to shorter wavelengths will be examined as well as concepts to realize electrically injected devices.
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