| Light-emitting diodes(LED) have been applied in increasing fields because of their advantages of high efficiency, long lifetime, solid state emission and flexible drive. Currently, Gallium Nitride(GaN) based LEDs are the most studied and the most widely used, because of the GaN-based LEDs are able to acheve deep ultraviolet to near infrared emission by reasonable adjusting indium content in the InGaN ternary compounds active layer. However, the LEDs’ efficiengcy would be degraded greatly with the passage of time induced by poor thermal management, efficiency droop and unmatched substrate. And simultaneously, limited size of active layer in LED and low thermal conductivity, inefficient heat disspation in substrate will result the pn junction temperature of LED increased rapidly. Therefore, the characteristic of lifetime and reliability of LED can be characterized by determining the pn junction temperature, and provide help for the picking of light-emitting diode. In view of this, A fast and efficient method for pn junciton temperature measurement was developed based on the relationship between the emission spectrum of the semiconductor material itself and temperature in this thesis, the main contents and results are including:1. A pn junction temperature measurement system and prototype was set up based on the relationship between the semiconductor fluorescence spectra, corresponding to the width of bandgap, and the temperature. At first, a linear dependence of its’ electroluminescence peak of light-emitting diode and the temperature was built by experiment. Then, a mixed curve model and algorithm conbined with Gauss and Lorenz function were developed for the spectrum of light-emitting diodes, and a complete, non-contact prototype was prepared, which can determine the pn junction temperature rapidly and accurately through the measurement of sprectrum of light-emitting diode. At last, the developed system and method was validated and applied. The determination system based on spectrum method has high test speed, with only30ms for a single spectrum acquisition, high test precision up to±1℃, good repeatability and reproducibility. The comparative study results betweent the traditional forward voltage method indicate that the stability of the calibration coefficients in spectrum method is30times higher than that in forward voltage under different calibration current amplitudes and sample batches. The results also show that the spectrum method is insensitive to calibration current amplitudes and sample batches, and give a much wider applicability than the forward voltage method.2. The influence of indium content in InGaN active layer on the GaN-based blue and green LEDs’ emission properties and calibration coefficients of pn junciton temperature were investigated. According to the results of the photoluminescence with varied excitation power, temperature and electroluminescence as function of variable injection current, temperature in GaN-based blue, green LEDs with different wavelengths, it is show that the indium content tends to the formation of localized indium-rich states, which the luminescence mechanism of light-emitting diode by the bimolecular(exciton) radiative combination is mainly occurs in these indium-rich localized area. Basically, there is a linear relationship between the indium content and emission peak position of the LEDs. The effect of indium-related localized states can lead to blueshift of the spectral peak, and rapid broaden of the spectral full width at half maximum; while, the screening of the built-in electric field introduces blueshift of the spectral peak, but narrows the spectral full width at half maximum of the spectrum. The photoluminescence and electroluminescence of the light-emitting diodes influenced by localized states and built-in electric field are depend on the content of indium content. In samples with low content of indium(<17%), the affect of localized states are dominate in both PL and EL experiment; in samples with lightly higher content of indium(19~26%), the localized states’ effect is more important, and the screening effect of the built-in electric field dominates in photoluminescence experiment. The calibiration coefficients of the pn junction temperature in blue and green LEDs were depend on sources. For the samples with same sources and emission in a certain range, the calibiration coefficients of the pn junction temperature and the localiezd states parameters decrease with increasing indium.3. The principle of deteminatation of chip’s pn junction temperature in light-emitting diode lamp by spectrum method was studied, a prototype for pn junction temperature measurement based on this principle was developed and well applied in practical engineering project. A simplified heat dissipation model for light-emitting diode lamp was developed on this basis, the effective heat dissipation parameters such as the generation rate and the removal rate of the temperature difference were proposed. The effective heat dissipation parameters were investigated with the environmental change by the condition of different environment temperatures, air condition at room temperature and duty cycles of driven pulse currents. A linearly dependence of the generation rate of temperature difference on ambient temperatures and the duty cycles of the driven current was observed with slopes about0.04and0.027, respectively. The dispersal rate of the temperature difference was basically not influenced by these effects. At the same time, it was found that the temperature rise of the pn junction temperature of light-emitting diode was sensitive to outside air conditions. Compared with closed ambient, in open environment, the temperature rise curve of the light-emitting diode will show obviously segmented cooling characteristics. In steady state, the pn junction temperature rise of light-emitting diode lamp are approximately equal to the ratio of the generation rate and the dispersal rate of the temperature difference of the lamp and almost increased synchronously with the input current power. |
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