| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 94 === In this dissertation, a systematic technique for numerical modeling of the current-voltage characteristics (I-V) for light-emitting diodes (LEDs) based on current transport mechanisms is proposed. The revised Shockley equation is employed under the consideration of nonideal effects, inclusive of series resistance and nonradiative recombination, leading to the diffusion-recombination model. The two-step iteration combined with the nonlinear regression technique to extract physical parameters for diodes, using a simple physical-based current-voltage model is demonstrated. The method has been applied to a wide variety of LEDs, and found to be an accurate and systematic technique for extracting diode parameters. The calculated recombination currents quantify the Shockley-Read-Hall recombination involving with localized states in LEDs, which can reveal the epitaxial quality for engineers. It has been found that the analyzing regime should be carefully chosen, for the adequate carrier transport phenomena. Frequently, the GaN-based LEDs bears higher forward voltage than the AlGaAs or AlGaInP-related LEDs, due to the high dislocation density in the epilayers. The various sets of traps have different trap-filling behaviors, which reflect on the I-V characteristics. Conversely, one can speculate the trap-filling process from the I-V plot.
The extracted parameters are zero-bias recombination current, reverse-bias saturation current, and series resistance. These parameters consists of the particular parameter for recombination-diffusion crossover, at which the recombination and diffusion currents have the same magnitude, indicating the theoretical internal quantum efficiency of 50%. In this dissertation, the recombination-diffusion crossover is proposed to examine the validity of the LED analyses by excluding the currents except for diffusion and recombination. The numerical recombination-diffusion crossover is in good accordance with the experiment at the adequate analyzing regime, which demonstrates the accuracy for the diffusion-recombination model. Consequently, the derived crossover reveals the optical efficiency for LEDs: The lower value for the crossover voltage, the shorter the trap-filling process and hence the lower value for forward voltage (operating voltage at 20 mA).
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