Influence of sidewall grating etching depth on GaN-based distributed feedback laser diodes

Conventional sidewall gratings in GaN-based distributed feedback (DFB) laser diodes (LD) have a thick p-type layer, which may cause current spreading and carrier-induced anti-guiding effects, severely deteriorating the lasers performance. In this study, we report a novel fabrication technology to not only reduce the remaining p-type layer in the sidewall gratings but also realize close-coupled sidewall gratings. Afterwards, we further investigate the influence of the sidewall gratings etching depth on GaN-based DFB LDs. The results show an almost unchanged current injection efficiency, nearly coincided I-V curve and a near-field emission width for shallow etched structures, which indicate that the current spreading is neglectable in GaN-based ridge structure LDs. Based on this analysis, GaN-on-Si DFB LDs with an emission wavelength of 414 nm, full width at half maxima of 22 pm, and side mode suppression ratio of 19.1 dB were realized.