Optimisation of 670 nm strained-quantum-well laser diodes for high-temperature operation

The paper is concerned with the optimisation of the active region of Ga_xIn_1-xP/(Al_0.5Ga_0.5) _yIn_1-yP lasers to produce low-threshold-current, 670 nm devices operating up to 400 K. By means of theoretical calculations, we have examined the relative merits of various well-composition (x)/well-width combinations and predict a minimum threshold current as a function of gallium content, as is the case with 633 nm lasers. The decrease in threshold current with decreasing well width (and decreasing gallium content) is due both to a decrease in the number of subbands in the quantum well and to an increase in the splitting of the valence bands caused by increasing strain. The increase in threshold current for very thin wells is due to increasing broadening of the gain spectra by well-width fluctuations and an increasing contribution from thermally activated leakage current. We predict an optimum threshold current density for a two-well, 68 Å well width and 41% gallium composition device for operation at 670 nm and 400 K, for L=250 μm and R₁=R₂=0.3