What is the problem with GaN-based VCSELs?
2013 13th International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD)
In contrast to the impressive progress of GaNbased edge-emitting lasers in recent years, III-nitride vertical-cavity surface-emitting lasers (VCSELs) still exhibit severe performance limitations. Using advanced device simulation, this presentation evaluates design and material issues with different GaN-VCSEL concepts and identifies performance limiting internal mechanisms. Similar to widely used GaAs-based vertical-cavity surface-emitting lasers (VCSELs), GaN-based VCSELs are expected to show
... expected to show various advantages over their edge-emitting counterparts, including lower manufacturing costs, circular and low-divergence output beam, single longitudinal mode emission, low threshold, high-speed modulation, high-density two-dimensional arrays, wafer-level testing, and longer lifetime. Potential applications of GaN-VCSELs include laser display, solid-state lighting, high-density optical data storage, high-resolution printing, low-cost optical communication, and bio-sampling. However, in contrast to the success of GaNbased edge-emitting lasers in recent years, GaN-VCSELs still face significant challenges. 1 One of the key material problems is the poor quality of AlGaN/GaN distributed Bragg reflectors (DBRs) due to the large lattice mismatch of GaN and AlN. A possible solution is the use of one or two dielectric DBRs. However, the employment of dielectric DBRs on both sides of the VCSEL cavity requires the removal of the majority of the GaN substrate combined with a precise control of the remaining cavity length. 2 This presentation evaluates different current-injected GaN-VCSEL design concepts that show room-temperature (RT) continuous-wave (CW) operation. The design of VCSELs in general is very demanding and numerical simulation is often used for design optimization. 3 We here employ the laser simulation software PICS3D 4 that self-consistently combines the computation of carrier transport, energy band structure, optical gain, optical modes, and self-heating. The transport model includes drift and diffusion of electrons and holes, Fermi statistics, built-in polarization and thermionic emission at hetero-interfaces, as well as photon emission, Auger recombination, and defect-related Shockley-Read-Hall (SRH) recombination. For the quantum wells, Schrödinger and Poisson equations are solved iteratively to account for the