Experimental investigation of thermally induced power saturation in vertical-cavity surface-emitting lasers

The physical processes responsible for power saturation and roll-over in vertical-cavity, surface-emitting laser diodes (VCSELs) have been investigated experimentally. Material gain spectra for 810 nm wavelength, AllnGaAs/GaAs VCSELs have been collected over a range of injection currents and temperatures. These data, together with knowledge of the threshold gain, allow the reconstruction of the output power characteristics. By using gain data taken at a temperature of 300 K, the structure-determined influence of mode detuning is studied in isolation from intrinsic material-related effects, such as thermally excited carrier leakage and gain reduction due to thermal broadening of the carrier distributions. The results show that, for these devices, the power roll-over is predominantly due to the thermally induced changes in the carrier distributions, rather than the movement of the lasing mode relative to the gain spectrum.