Photoluminescence Spectral Analysis Of GaN-based UV-LED

GaN-based LED has many advantages such as small volume, long life, high luminous efficiency and environmental protection. GaN-based Ultraviolet light-emitting diode (UVLED) has gained more attention as the process and structure of blue and green LED having been mature and perfect. However, LED with shorter wavelength still has many difficult problems to be solved, such as big mismatch constant with substrate, difficult growth of high Al components and difficult p-type doping process, which make the luminous efficiency of GaN-based UVLED too low to meet the demand of business, it is particularly important to improve luminescence property of GaN-based UVLED. LED is prepared on sapphire substrate by Metal-organic Chemical Vapor Deposition (MOCVD) system and analyzed by the method of photoluminescence, X-ray diffraction (XRD) and Origin software. In this thesis we study the influence of different Quantum well’s structure and impurities on the optical performance of LED.1.In a proper range, the light power increases with well widening. This is because with the well widening, more carriers are trapped within the quantum wells, thereby the luminous power can be enhanced. However, broaden well will separate the wave function of electron and hole and reduce the radiative recombination efficiency. Experimental results show that LED luminous efficiency is the largest when growth time of well layer last 216 s.2.Luminous efficiency of LED reduces and then increases with Al components increasing in barrier layer. This is because lattice mismatch between barriers and wells becomes lager and crystallization quality become worse, which causes brightness diminished; on the other hand, with more Al components, quantum wells deepen, more carriers are trapped within the quantum wells, and radiative recombination efficiency rises. Experimental results show that luminous efficiency can be optimal when Al components equal to 5 percent. For UVLED with shorter wavelength, Al components should increase.3.Photoluminescence(PL) spectrum of UVLED is analyzed by the method of Gauss fitting peak. According to the peak wavelength, experimental results show that it is shallow acceptor impurity CN exists in the superlattice who affects the luminous efficiency. The existence of the peak cause by superlattice seriously influence the consistency of the LED wavelength, so we can adjust Al composition in wells to make its wavelength close to the quantum well’s, thus reducing the influence on luminescence property. By adjusting the different components of In in quantum wells, we analyze unintentional doped defect and doped impurity defect which may affect the spectrum of LED. Fitting peaks of PL spectra, we find existence of CN impurities in the quantum well, whose energy level becomes closer to valence band and ionization energy decreases with the increase of In composition. At last technique processes such as increasing V/III ratio, raising temperature and reducing growth rate are proposed to reduce the concentration of impurity defects, and then reducing its influence on the optical performance of the device.