Tradeoffs in the Realization of Electrically Pumped Vertical External Cavity Surface Emitting Lasers

The design and realization of substrate emitting 980-nm electrically pumped vertical-external-cavity surface-emitting lasers (EP-VECSELs) is reported. A method to characterize the detuning of the cavity and spontaneous emission of the epitaxial material is described, and an experimental study of the effect of substrate doping on the operating characteristics of devices is presented. A reduction in optical loss and enhanced current-gain characteristics with a reduction in substrate doping from 2 × 10⁸ to 4 × 10¹⁷ cm^-3 is demonstrated. Spatial carrier distributions, evidenced by near-field profiling of devices without external feedback indicate similar current spreading behavior for the two-substrate dopings. Devices with diameter greater than 70 μm and current spreading layer thickness of 100 μm are shown to suffer from nonuniform carrier injection into the active region. Power scaling properties of the devices are investigated in both pulsed and CW operation. We realize devices with CW powers of 133 mW at 981 nm from a 150 μm device with 4 × 10¹⁷ cm^-3 substrate doping at 0 °C, which is limited by nonoptimal cavity-gain peak detuning.