High-differential-quantum-efficiency, long-wavelength vertical-cavity lasers using five-stage bipolar-cascade active regions

We present five-stage bipolar-cascade vertical-cavity surface-emitting lasers emitting at 1.54μm grown monolithically on an InP substrate by molecular beam epitaxy. A differential quantum efficiency of 120%, was measured with a threshold current density of 767A∕cm2 and voltage of 4.49V, only 0.5V larger than 5×0.8V, the aggregate photon energy. Diffraction loss study on deeply etched pillars indicates that diffraction loss is a major loss mechanism for such multiple-active region devices larger than 20μm. We also report a model on the relationship of diffraction loss to the number of active stages.