Effect of Carrier Leakage on Optimal AR Coatings in Midinfrared Interband Cascade Lasers

Variation of leakage current in interband cascade lasers (ICLs) with different carrier concentrations achieved by coating the facet with antireflections (AR) coating was experimentally studied. Single-layer Al2O3 and double-layer ZnS-YF3, ZnS-SiO2, and Ti2O5-SiO2 AR coatings are applied to midinfrared (mid-IR) ICL devices to achieve reflectance ranging from 0.15 to 7 × 10^-4. By monitoring the laser performance before and after coating, it was observed that, for lower reflectivity coatings, the leakage current appreciably rises with increasing carrier concentration, thus diminishing the slope efficiency improvements and, in fact, degrading the slope efficiency at very low reflectance. It was observed that the ratio of leakage to threshold current could increase by 17% for high carrier concentrations at very low AR coating values. The results also allow for experimental optimization of AR coatings for increased slope efficiency in mid-IR ICLs. Therefore, in this paper, we propose an optimal value for the AR coatings in order to maximize the power in ICLs.