OPTIMIZATION OF 670-NM STRAINED-QUANTUM-WELL LASER-DIODES FOR HIGH-TEMPERATURE OPERATION

The paper is concerned with the optimisation of the active region of G axIn1-xP/(Al0.5Ga0.5)yIn1-yP lasers to produce low-threshold-current, 670 nm devices operating up to 400 K. By means of theoretical calculat ions, we have examined the relative merits of various well-composition (x)/well-width combinations and predict a minimum threshold current a s a function of gallium content, as is the case with 633 nm lasers. Th e decrease in threshold current with decreasing well width (and decrea sing gallium content) is due both to a decrease in the number of subba nds in the quantum well and to an increase in the splitting of the val ence bands caused by increasing strain. The increase in threshold curr ent for very thin wells is due to increasing broadening of the gain sp ectra by well-width fluctuations and an increasing contribution from t hermally activated leakage current. We predict an optimum threshold cu rrent density for a two-well, 68 angstrom well width and 41% gallium c omposition device for operation at 670 nm and 400 K, for L = 250 mum a nd R1 = R2 = 0.3.