Luminescence Modes in the Semiconductor Micro Structure

In the semiconductor microstructure there are two different modes: Fabry-Perot modes and whispering gallery modes. In the band-edge region, there are strong coupling between the exciton and the confined photon, which will lead a quasi-particle: polariton. In a ZnO semiconductor nanobelt with a transverse size of m, more than 20 modes are observed in the band-edge region, and more than 60 modes are observed in the visible region. The theoretical results demonstrate that in the band-edge region the luminescence modes are determined by the polariton modes. Because of the coupling between the exciton and confined photon, the dispersion relation is nonlinear in the band-edge region, while it is linear in the visible band. The theoretical fitting results show that the quality factor of the cavity is decreased from 280 to 70 with the increase of the wavelength from ultra-violet to visible band. For the whispering gallery modes, the multiple total internal reflections (TIR) play a key role. As the reflection in the Fabry-Perot modes is perpendicular, there is no phase difference between the s and p polarizations. However, for the whispering gallery modes, there is obvious phase difference between the s and p polarizations in the TIR, which will lead two kinds of whispering-gallery modes. In our rectangle ZnO samples with a size of m, more than 40 luminescence modes are observed in the waveband from 530 to 655 nm. The appearance of the luminescence spectra shows that the adjacent peaks are completely different. The mode spacing convinces that there two different kinds of luminescence modes, which correspond to the s and p polarizations, respectively. The adjacent modes spacing is completely in accordance with the theoretical phase difference of the s and p polarization. Therefore, our experimental results provide an adequate evidence that there are two kinds of whispering gallery modes in the rectangle micro structure.