The influence of strain on the small signal gain and lasing threshold of GaInAs/GaAs and GaAs/GaInAlAs strained-layer quantum well lasers

Results of calculations on how band-structure changes introduced by strain affect the gain spectra in multi-quantum-well (MQW) lasers are presented. Reduction of threshold injection as well as increased TE mode emission occurs for the compressive-strain case. In tensile strain the thresholds for TE and TM modes approach each other. Experimental studies on the compressive-strain laser structures show that the spontaneous and lasing spectra shift to longer wavelengths, the threshold current density is reduced, and a more rapid rise of gain with increased injection occurs. The output spectrum shifted from the 959-962 nm range for the GaInAs devices with 20% In to the 1033.5-1041.0-nm range for devices with 30% In. The threshold current density decreased with increasing strain, as expected from the theory. The modal gain of the devices and the peak modal gain were shown to rise very quickly with increased injection. This qualitatively agrees with the expected decrease in hole density of states brought about by strain, which could cause the hole states to be more rapidly filled and result in a more rapid rise in the material gain