Output characteristics of laser diodes (LDs) emitting at 808 nm with 3 different thicknesses of waveguide-layer made from Al0.65Ga0.35As (0.4,0.5 and 0.6 μm) and 3 different AlGaAs-based large optical cavities (LOC) (Al0.65Ga0.35As-1 μm,Al0.6Ga0.4As-1.5 μm and Al0.45Ga0.55As-2 μm) were studied. P-I curves of these different structures were simulated,threshold currents were computed by the means of linear fitting,and characteristic temperatures of these devices was calculated. The experimental results authenticated the theoretical calculation results. The research of different waveguide-layer thickness showed that when thickness of single quantum well was fixed,the thicker the waveguide layer was,the higher the characteristic temperature was,and the better the device performance. The study of different large optical cavity indicated LD with 2 μm-LOC was the best of those three as a result of an aluminum content of x=0.45 yielding an effective vertical spot size of 1.0 μm and a lower electrical resistance.