We designed and fabricated a two dimensional high contrast subwavelength grating (HCG) mirrors. The computer-aided software was employed to verify the structural parameters including grating periods and filling factors. From the optimized simulation results, the designed HCG structure has a wide reflection stopband (reflectivity (R) >90%) of over 200 nm, which centered at telecommunication wavelength. The optimized HCG mirrors were fabricated by electron beam lithography and inductively coupled plasma process technique. The experimental result was almost consistent with calculated data. This achievement should have an impact on numerous photonic devices helpful attribution to the integrated HCG VCSELs in the future.
We report on the numerical analysis of the electrical and optical properties of current-injected III-N based vertical-cavity surface-emitting lasers (VCSELs) with three types of current confinement schemes: the conventional planar-Indium Tin Oxide (ITO) type, the AlN-buried type without ITO, and the hybrid type. The proposed hybrid structure, which combines an ITO layer and an intracavity AlN aperture, exhibits not only a uniform current distribution but also an enhanced lateral optical confinement. Thus, the hybrid type design shows a remarkably better performance including lower threshold current and series resistance compared with the planar-ITO type and the AlN-buried type. Furthermore, the multi-transverse mode lasing behavior induced by strong index guiding of the AlN aperture is suppressed to single transverse mode operation by reducing the aperture size. Such design provides a powerful solution for the high performance III-N based VCSELs and is also viable by using current state of the art processing techniques.
We investigate the influence of passivation structure on the optical mode distribution and LI characteristics for the edge emitting AlGaInP-GaInP visible laser diode (LD). For traditional single-layer Si3N4 or SiO2 passivation designs, the modification of dielectric layer thickness can determinate the lateral near-field confinement and change the horizontal far-field (FF) divergence. By increasing the film thickness, the non-radiation absorption come from Au-Ti can be improved and it leads to a narrow FF divergence beam. As continue to increasing the thickness, thicker passivation provides a better confinement factor and then the far-field pattern turn to be wider. For LI characteristics, it is necessary to deposit a thick enough passivation to reduce metal absorption. However, it cause much thermal energy accumulated in the ridge waveguide and deteriorate the quantum efficiency as adopting a too thick dielectric layer. Finally, we demonstrate a high power AlGaInP-GaInP multi quantum wells (MQWs) LD adopted a high-reflectivity passivation to enhance the LI characteristics and keep a suitable far-field divergence angle simultaneously. Under the design of threepair optical thin films, it cannot only avoid the metal absorption but also enhance emitting efficiency and heat dissipation by using a high reflective and good thermal conductive Al2O3/Ta2O5 multilayer. The measured room-temperature threshold current (Ith) and characteristic temperature (T0) can be arrived 44.5mA and 104.2K at 16.4° far-field divergence.