Anomalous above-threshold spontaneous emission in gain-guided vertical-cavity surface-emitting lasers

Anomalously large decrease in spontaneous emission is observed in gain-guided vertical-cavity surface-emitting lasers after the onset of lasing. By analyzing two-dimensional profiles of the lasing mode and carrier density, we found that this unexpected phenomenon originates from the contraction of transverse lasing mode size. Under the condition of the constant modal gain, it is explained that the above-threshold average carrier density could decrease in contradiction to the general understanding. Unless this anomalous effect is taken into account properly, nontrivial errors could occur in determination of the external quantum efficiency. © 1996 American Institute of Physics. @S0003-6951~96!01116-X#