Measurement And Analysis Of The Photoluminescence Of InGaN/GaN Quantum Wells

From the beginning of the 1990s, there has been worldwide upsurge of researching high-brightness LED, based on which the solid illumination is developing rapidly. Since high-brightness LED adopts double hetero-structure, it demands that the material should have good lattice match. This need put a strict limit on the material system which is used for the hetero-junction LED.Theâ…¢-â…¤nitride semiconductor materials have excellent photoelectric performance and stable chemical properties, they can work under those conditions such as high temperature, acid, alkali and radicalization, moreover, they have wide band-gap range. As a result, they have considerable affinity in the area of high-power electric apparatus and have already attracted lots of researchers both internal and overseas. Theâ…¢-â…¤nitrides which interest people most are AlN, GaN, InN and their alloys. By controlling their respective component, their band gap can continuous change from 0.7eV of InN to 3.4eV of GaN until 6.2eV of AlN,which cover the entire visible light district and expand to the scope of the UV, consequently are fit for making high-brightness LEDThis paper is legislated under these circumstances, firstly by the experimental approach of photoluminescence, we investigated the luminescence characteristics of the wide band-gap semiconductor quantum wells, compared the luminescence performance of two kinds InGaN/GaN multi-quantum well(InGaN/GaN MQW) which are separately grown on the sapphire subatrate and free-standing GaN substrate. Then we analyzed the luminescence characteristics at low temperature of the InGaN/GaN MQW grown on the free-standing GaN substrate. At last, we investigated and analyzed, by the experimental approach of atomic force microscope(AFM), power-dependent photoluminescence and cathode luminescence(CL), the luminescence characteristics of four InGaN/GaN single quantum wells, of which all the other growth conditions are all the same except the growth temperature. We obtained the following conclusions:1. Under the same excitation power density, the Photoluminescence intensity of the InGaN/GaN MQW grown on the free-standing GaN substrate is obviously higher than the one grown on the sapphire subatrate. It shows that the expansion of defects have an important effect on the recombination efficiency.2. Under the condition of high power excitation at any temperatures, the recombination of band edge free carriers (or free excitons) dominates, and further recombination intensity weakens with the temperature or excitation power decreased. While under the condition of low power at lower temperatures than room temperature, the recombination of bound excitons introduced by the localized states dominates the photoluminescence, and the recombination intensity increases monotonously with the temperature and excitation power decreased.3. Blue shift appears in the band edge recombination when the sample temperature raises or excitation power enlarges. While the peak wavelength of the localized bound excitons recombination has no obvious change with the sample temperature and excitation power.4. The full width at half maxima (FWHM) of the band edge recombination is independent of the temperature and excitation power, while the FWHM of the local bound excitons recombination increases with the excitation power.5. Whether the phase-seperation phenomena will appear in the InGaN system is primaly related to the temperature, and meanwhile the lattice mismatch between GaN and InGaN could affect the phase-seperation in InGaN epitaxial layer.6. In the sample which is grown under 670 degree, phase-seperation appears and we also find InN-rich quantum dots form in InGaN system.