High-efficiency superlattice graded-index separate confining heterostructure lasers with AlGaAs single quantum wells

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Abstract
Superlattice graded-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 40%, 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 graded-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 room-temperature photoluminescence. They include the n=2 states of the quantum well and the confined states (n=3, 4,...) extending into graded-index regions. Additional states resulting from the X conduction band in the graded-index regions appear at energies near the top of the well (∼ 2 eV at room temperature) for the structures evaluated in this study. The growth of these structures and the limitations of the devices’ performance under continuous wave conditions at the shorter wavelengths are reviewed.