InGaN/GaN 발광다이오드 내부양자효율의 온도의존성에 대한 연구

Abstract

본 논문에서는 InGaN/GaN 청색 발광다이오드(light-emitting diode, LED)의 온도 변화에 따른 내부양자효율(internal quantum efficiency, IQE) 의 변화를 연구하였다. 한양대에서 개발한 전류 의존 전기루미네선스(current-dependent electroluminescence, CDEL) 방법과 상온에서의 시간분해 광루미네선스(time-resolved photoluminescence, TRPL) 방법을 이용하여 넓은 온도 범위구간에 걸쳐 전기적, 광학적 특성을 관찰하였다. 첫번째로 인듐 함량이 다른 청색 발광다이오드와 녹색 발광다이오드를 비교하여, 인듐 함량에 따른 효율의 감소량(efficiency droop의 양), 최대 내부양자효율 값, 내부양자효율 최대값이 측정되는 전류구간 등을 알아보았다. 이를 통해 온도가 낮을수록, 인듐 함량이 높을수록 효율저하가 심화되는 것을 알 수 있었다. 실험 결과와 고찰을 통해 온도와 전류변화에 따른 해석모델을 제시하였다. 두번째로 패키지된 청색 발광다이오드의 시간에 따른 광루미네선스 세기의 감소를 측정하였다. 온도 변화에 따라 운반자 수명을 발광재결합과 비발광재결합 수명으로 분리 측정하였고, 이를 통해 내부양자효율을 계산하였다. 온도가 낮아짐에 따른 재결합 수명의 변화와 내부양자효율의 관계에 대해 고찰하였다. 내부양자효율의 변화경향이 비발광재결합 수명의 변화와 밀접한 관련이 있음을 알 수 있었다.|In this thesis, the temperature dependence of the internal quantum efficiency (IQE) of the InGaN/GaN blue light-emitting diodes (LEDs) was studied. The electrical and optical characteristics were observed at various temperatures by using the time-resolved photoluminescence (TRPL) and the current-dependent electroluminescence methods developed at Hanyang University. Firstly, comparisons of two samples that have different indium contents (blue and green LEDs) were made in terms of the efficiency droop, the value of maximum IQE, and the current at the maximum IQE. From the results, it was found that the efficiency droop gets worse at lower temperature and higher indium content. The temperature and current-dependent analysis model was proposed to explain the experimental results. Secondly, the reduction of the photoluminescence intensity was measured at various temperatures in a packaged blue light-emitting diode. At different temperatures, the carrier lifetime was measured and separated into radiative and nonradiative recombination lifetimes. These were then used in the calculation of IQE. The relationship between the recombination lifetime and the IQE at different temperatures was investigated. A close relation was observed between the change of the IQE and the change of the nonradiative recombination lifetime.; In this thesis, the temperature dependence of the internal quantum efficiency (IQE) of the InGaN/GaN blue light-emitting diodes (LEDs) was studied. The electrical and optical characteristics were observed at various temperatures by using the time-resolved photoluminescence (TRPL) and the current-dependent electroluminescence methods developed at Hanyang University. Firstly, comparisons of two samples that have different indium contents (blue and green LEDs) were made in terms of the efficiency droop, the value of maximum IQE, and the current at the maximum IQE. From the results, it was found that the efficiency droop gets worse at lower temperature and higher indium content. The temperature and current-dependent analysis model was proposed to explain the experimental results. Secondly, the reduction of the photoluminescence intensity was measured at various temperatures in a packaged blue light-emitting diode. At different temperatures, the carrier lifetime was measured and separated into radiative and nonradiative recombination lifetimes. These were then used in the calculation of IQE. The relationship between the recombination lifetime and the IQE at different temperatures was investigated. A close relation was observed between the change of the IQE and the change of the nonradiative recombination lifetime.