The development of GaN-based vertical-cavity surface-emitting lasers (VCSELs) has been progressing rather fast in the past few years. Owing to the special device structures of GaN-based VCSELs, novel designs have to be incorporated in order to achieve high performance in terms of low threshold, high efficiency, stable mode profile and polarization direction. We demonstrate an easy and cost-effective way to realize index-guiding structure that significantly lowers the threshold and observe the transverse mode spectra of guiding and antiguiding VCSELs. We also realize the GaN-based VCSEL with high-contrast grating (HCG) as the top mirror and achieve polarization control over manipulation of HCG parameters.
We demonstrate the first electrically injected GaN-based VCSEL with a TiO2 high-contrast grating (HCG) as the top mirror. The TiO2-HCG rested directly on the n-GaN without an airgap for mechanical stability. A VCSEL with an aperture diameter of 10 μm had a threshold current of 25 mA under pulsed operation at room temperature. Multiple longitudinal modes coexist around 400 nm, each TM-polarized with a linewidth of 0.5 nm (spectral resolution limited). This first demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as post-growth setting of resonance wavelength.
We report a GaN-based VCSEL with a high-contrast grating (HCG) as the top mirror. The HCG consisted of TiO2 and rested directly on the n-GaN without an airgap or the use of any DBR layers to boost the reflectivity. The full VCSEL structure was optically pumped at room temperature and showed a lasing threshold of approximately 0.69MW/cm2 and a lasing wavelength at 369.1 nm. This first demonstration of lasing in a HCG GaN-based VCSEL opens up the possibility to explore all the potential benefits of HCGs in the blue and ultraviolet spectral regime.
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