| Ⅲ-Nitride semiconductor have direct band-gap which covers a wide spectrum range from infrared to ultraviolet and are ideal materials for the solid-state lighting and display applications. Although the great progress of Ⅲ-Nitride materials and GaN-based LED has been made, some questions are still not yet solved, such as strain dependence of optical properties of high In-content InGaN, efficiency droop effect of Ⅲ-Nitrid LED and as on. In this thesis, by using k·p method we in detail investigate the optical properties of a-/c-plane wurtzite-InN films with various in-plane strain and the emission efficiency of GaN-based LED with novel structure or SP coupling. The main results are listed as follows:(1) The optical properties of c-/a-InN film are investigated by the 8×8 k·p method including the influence of carrier density. By the formula, the imaginary parts of ordinary and extraordinary dielectric function of c- and a-plane InN near band edge are presented. For c-plane InN, the shift of ordinary absorption edge in the case with isotropic in-plane strain in comparison to the unstrained one is very small. For a-plane InN, the splitting between the ordinary and extraordinary components can be modulated with different anisotropic in-plane strain. Furthermore, the splitting can be obviously changed by the carrier density. The larger the splitting is, the more the drop of the splitting with carrier density is. The spontaneous emission spectrum shows the ratio of peak intensity of y-and z-polarizations increases with enhancement of the splitting. At the strain configuration (-0.37,0.18), the ratio of a-InN film is as large as 3.67 times.(2) The optical properties of InGaN/GaN quantum well with insertion of ultrathin InN layer are investigated in the green spectral regime by using the effective mass theory. The total spontaneous emission radiation recombination rate can be optimized by modulating the position of InN layer in the InGaN QW. The obtained optimization structure is 0.9nm In0.17Ga0.83N/0.3nm InN/1.7nm In0.17Ga0.83N QW. The intermixing effect at the interface between InN and InGaN layers can obviously reduce the optical gain and red-shift the emission wavelength. However, as compared to the conventional quantum well structure, the material gain of novel structure can still be significantly enhanced. Thus the green gap for GaN-based laser diode or LED can be expected to overcome by using the novel structure.(3) The spontaneous emission (SE) rate into Surface Plasmon Polariton (SPP) mode for the InGaN/GaN quantum well (QW) with Surface Plasmon (SP) coupling is first derived in the presence of SP fringing field using Fermi’s golden rule. The optical properties of the Ag coating InGaN/GaN QW structure is in detail investigated by using the formula. The numerical results show the peak intensity of SPP mode is one order of magnitude larger than that of TE mode, which indicates the energy of electron-hole pairs can be efficiently transferred to the SPP mode. Due to the limit of extraction efficiency of SPP-mode, the difference (△η) between SP-enhanced IQE (ηspp) and the original IQE (ηc) has a maximum at ηc=6%-25%. Moreover, the internal quantum efficiency of SP-enhanced LED only slightly decreases with increasing the current density which implies the efficiency droop can be suppressed by SPP-coupling. The peak wavelength of SPP mode is red-shifted as compared to that of TE mode at the same current density due to the weakly carrier screening. At 20A/cm-2, the red shift is between 5nm and 9nm, which is basically consistent with the experimental result.
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