GaN laser diodes for quantum sensing, optical atomic clocks, and precision metrology

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

“…with a large full width at half maxima (FWHM) of the lasing spectrum (>1 nm), which cannot fulfill the requirements of atom spectroscopy, atomic clocks, sensing, metrology, underwater LiDAR, and medical diagnostics [6][7][8]. Therefore, the monolithic integration of gratings on the conventional GaNbased FP cavity LDs to select a single longitudinal mode and then narrow the spectral linewidth, which is also known as GaN-based distributed feedback (DFB) LD [6][7][8][9][10][11][12], has been extensively studied.…”

“…Ridge grating structures avoid the epitaxial regrowth but may seriously affect the uniformity of the current injection and hence, the threshold current [8,9]. Therefore, easily fabricated sidewall grating structures with nearly no negative impact are widely studied [10][11][12]. To increase the optical coupling coefficient, researchers often fabricate the sidewall gratings and ridges simultaneously to ensure the sidewall grating is close enough to ridges [10,11].…”

“…Therefore, easily fabricated sidewall grating structures with nearly no negative impact are widely studied [10][11][12]. To increase the optical coupling coefficient, researchers often fabricate the sidewall gratings and ridges simultaneously to ensure the sidewall grating is close enough to ridges [10,11]. Thus, the sidewall gratings are often formed in the ridge, and the unetched part of the sidewall gratings have a relatively thick p-type layer, especially including about 600 nm thick ptype AlGaN/GaN superlattice (SL) cladding layer with a high hole lateral mobility [13,14], which may not only cause current lateral spreading, deteriorating the current injection efficiency and hence the laser performance, but also stimulate a strong carrier-induced anti-guiding effect, seriously reducing the optical confinement and increasing the lasing threshold [15][16][17].…”