Carrier-Induced Energy-Gap Shrinkage in Current-Injection GaAs/AlGaAs MQW Heterostructures

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Abstract
Recombination radiation below the lowest confined particle transition energy observed in GaAs/AlGaAs multi-quantum-well heterostructure lasers was studied in comparison with that in conventional GaAs double-heterostructure lasers. The spontaneous emission shows lower-energy-side broadening in proportion to the 1/2.6 power of the injected carrier density for both the MQW structures and the conventional DHs. This carrier density dependence suggests that the observed low-energy-side broadening of the spontaneous emission is due to carrier-induced energy-gap shrinkage. The energy gap shrinkage in the MQW structures is considered theoretically by modifying the well-known bulk theory for gap shrinkage and taking the effective mass anisotropy into account. This theory is found to account satisfactorily for the observed lower-energy-side broadening. The results suggests that lasing below the lowest confined particle transition energy in MQW laser diodes is due to gap shrinkage rather than to LO-phonon participation as reported by other workers.