Impact of carrier injection and recombination on the −3 dB bandwidth for GaN-based VCSELs

In this study, we investigate the impact of the carrier transport and recombination on frequency response capability for GaN-based vertical-cavity-surface-emitting laser diodes (VCSELs). The carrier transport and recombination are manipulated by using composition-gradient quantum barriers and a p-type electron-blocking layer. The alloy composition-gradient approach is able to generate polarization bulk charges that favor the polarization self-screening effect to reduce the electric field at heterojunctions. This on the one hand suppresses the quantum confined Stark effect to increase the stimulated recombination rate in the active region. On the other hand, the Al-gradient design enables the decreased electron leakage level. Our results show that the -3 dB bandwidth can be improved either when the stimulated radiative recombination lifetime gets decreased or the escape time for electrons becomes long. As a result, the -3 dB bandwidth can be mostly increased by both decreasing the electron leakage level and increasing the stimulated radiative recombination rate.