InGaN/GaN Distributed Feedback Laser Diodes with Surface Gratings and Sidewall Gratings

Abstract

A variety of potential applications such as visible light communications require laser sources with a narrow linewidth and a single wavelength emission in the blue light region. The gallium nitride (GaN)-based distributed feedback laser diode (DFB-LD) is a promising light source that meets these requirements. Here, we present GaN DFB-LDs that share growth and fabrication processes and have surface gratings and sidewall gratings on the same epitaxial substrate, which makes LDs with different structures comparable. By electrical pulse pumping, single-peak emissions at 398.5 and 399.95 nm with a full width at half maximum (FWHM) of 0.32 and 0.23 nm were achieved, respectively. The surface and sidewall gratings were fabricated alongside the p-contact metal stripe by electrical beam lithography and inductively coupled plasma etching. DFB LDs with 2.5 μm ridge width exhibit a smaller FWHM than those with 5 and 10 μm ridge widths, indicating that the narrow ridge width is favorable for the narrowing of the line width of the DFB LD. The slope efficiency of the DFB LD with sidewall gratings is higher than that of surface grating DFB LDs with the same ridge width and period of gratings. Our experiment may provide a reliable and simple approach for optimizing gratings and GaN DFB-LDs.

Narrow-Linewidth GaN-on-Si Laser Diode with Slot Gratings

“…Due to the chemical inertness of GaN, such Bragg gratings are usually fabricated by dry etching [25,26]. The sidewalls of the grating often suffer from roughness, poor steepness, and etching damage due to mask deformation, limitation of the aspect ratio, and high energy ion bombardment during the dry etching [27][28][29]. This would result in a large optical loss and low internal quantum efficiency owing to the light scattering and surface nonradiative recombination.…”

10-Gbit/s Sky-Blue Distributed Feedback Laser Diode-Based Visible Light Communication

“…While DFB-LDs are now widely available at the telecom wavelengths, they are relatively unexplored at the visible wavelengths. Device development has shown InGaN-based DFB-LDs emitting at violet, blue, and green wavelengths [6][7][8][9][10], but aside from a recent report [11], their application to optical wireless communications is little-known.…”

Blue Laser Diode System With an Enhanced Wavelength Tuning Range

“…In a bid to address this shortcoming, two techniques have been widely explored in the literature to realize narrowband emission devices. Firstly, the monolithic approach employing grating structures in the form of distributed feedback (DFB) [9], [10], [11] and very recently, surface and sidewall DFB [12] gratings. These schemes demonstrated narrowband emission and are generally incorporated during the laser diode growth/fabrication process.…”