Superlattice gradedhyphen;index separate confining heterostructure lasers, with AlGaAs single quantum wells operating in the wavelength range from 700 to 845 nm, are reported. These structures have external power efficiency above 40percnt;, which is the highest reported to date over this entire wavelength range. By examining the performance of these structures as the thin quantum well active region is alloyed with aluminum, a better understanding of the dominant loss mechanism in thin single quantum well lasers results: it is concluded from this study that the carrier population of the higher energy states in the quantum well, and of states associated with the gradedhyphen;index regions, is the dominant carrier loss mechanism which limits the device performance. The energies of these states involving direct transitions are readily observed with roomhyphen;temperature photoluminescence. They include then=2 states of the quantum well and the confined states (n=3, 4,...) extending into gradedhyphen;index regions. Additional states resulting from theXconduction band in the gradedhyphen;index regions appear at energies near the top of the well (sim; 2 eV at room temperature) for the structures evaluated in this study. The growth of these structures and the limitations of the devicesrsquo; performance under continuous wave conditions at the shorter wavelengths are reviewed.
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