SPONTANEOUS EMISSION FACTOR OF A MICROCAVITY DBR SURFACE EMITTING LASER .2. EFFECTS OF ELECTRON QUANTUM CONFINEMENTS

A method for the theoretical analysis of the spontaneous emission factor (C factor) has been developed for microcavity DBR surface emitting lasers having various quantum-well active regions. It is shown that the C factor can be enlarged by the enhancement of mode density, the anisotropic emission, and the narrow spectral width in quantum wells. C approximately 0.6 may be obtained with GaAs-AlAs DBR's, 0.55-mu-m x 0.55-mu-m cross section of the cavity, three times vertically long cross section of quantum-wire active regions, and the spectral width of several nanometers at room temperature. This value can be further increased by utilizing a narrower spectral width expected at low temperature. For bulk and quantum film, the upper limit of the C factor is considered to be 0.5 due to the 50% probability of radiation energy coupled into one linearly polarized lasing mode. By the polarization selectivity of quantum wires, this limit can be enhanced to nearly 0.9, which is promising for the realization of thresholdless lasers.