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Extremely low threshold GRIN-SCH lasers with single and double active layers were prepared by molecular beam epitaxy as a result of an increased optical confinement, a significant reduction in the internal loss αi, and the increased gain constant β. Averaged Jth 250 A/cm2 and 160 A/cm2 for broad-area Fabry–Perot diodes of cavity lengths 380 and 1125 μm, respectively, and averaged external differential quantum efficiency ηD of 65–80 % were obtained.
W. T. Tsang (1982) studied this question.