The critical impact of the waveguide thickness on the optical and threshold behaviors of InGaN-based green laser diodes

We study the optical structures of green (520 nm) InGaN-based laser diodes (LDs) with the complex 1D transfer matrix method, in consideration of the anti-guiding effect and mode leakage into the substrate. Two characteristic thicknesses of the waveguide are found to play critical roles in the behavior of the LD threshold and the beam quality. When a minimum threshold is desired, there exists an optimal thickness (OT) of the waveguide, which is strongly affected by the index contrast of the structure and the anti-guiding factor of the active region. A proper waveguide thickness (WT) makes the structure more tolerant of the mode leakage and the anti-guiding effect. An intrinsic failure in the lasing mode emerges with improper WTs. When a complete elimination of the substrate mode is desired, the waveguide above a critical thickness (CT) is required. To compromise the threshold and the beam quality, an eclectic thickness, while a high composition in the waveguide is suggested.