Whispering-gallery mode structure in semiconductor microdisk lasers and control of the spontaneous emission factor

Abstract

The mode density and cross-sectional area of whispering-gallery modes of various possible polarizations existing in a microdisk cavity structure have been investigated and compared in some detail. Their variations with the disk thickness and radius have been calculated and the behavior of the spontaneous emission factor controlled by the microdisk structure have been shown. It is found that for a given microdisk thickness, the spontaneous emission factor increases with decreasing microdisk radius, but decreases after passing a maximum value. This non-monotonic behavior has never been noted before by others. The variation of spontaneous emission factor with respect to microdisk thickness also exhibits similar behavior. For a microdisk laser emitting at 1.5 μm wavelength, the enhanced spontaneous emission factor can barely exceed 0.2. A device configuration for improving the coupling between the whispering-gallery mode and the active region, and for leading the laser beam out of this high-Q microcavity is proposed, and its feasibility in realizing a thresholdless laser is discussed.