采用有机金属化学气相沉积技术在Si(111)衬底上生长蓝光多量子阱发光二极管(LED)结构，通过在量子阱下方分别插入两组不同厚度的InGaN/GaN超晶格，比较了超晶格厚度对LED光电性能的影响。结果显示：随超晶格厚度增加，样品的反向漏电流加剧；300 K下电致发光仪测得随着电流增加， LED发光光谱峰值的蓝移量随超晶格厚度增加而减少，但不同超晶格厚度的两个样品在300 K下的电致发光强度几乎无差异。结合高分辨X射线衍射仪、扫描电子显微镜、透射电子显微镜对样品的位错密度和V形坑特征分析，明确了两样品反向漏电流产生巨大差异的原因是由于超晶格厚度大的样品具有更大的V形坑和V形坑密度，而V形坑可作为载流子的优先通道，使超晶格更厚的样品反向漏电流加剧。通过对样品非对称(105)面附近的X射线衍射倒易空间图分析，算得超晶格厚度大的样品其InGaN量子阱在GaN上的弛豫度也大，即超晶格厚度增加有利于减小InGaN量子阱所受的应力。综合以上影响LED发光效率的消长因素，导致两样品最终的发光强度相近。%GaN based light-emitting diodes (LEDs) are subjected to a large polarization-related built-in electric field in c-plane InGaN multiple quantum well (MQW) during growth, which causes the reduction of emission efficiency. To mitigate the electric field, a superlattice layer with a numerous good characteristics, such as a small thickness, a high crystalline quality, is embedded in the epitaxial structure of LED. However, the effect of the superlattice thickness on the properties of LED is not fully understood. In this paper, two blue-LED MQW thin film structures with different thickness values of InGaN/GaN superlattice inserted between n-GaN and MQW, are grown on Si (111) substrates by metal-organic chemical vapor deposition. Electronic and optical properties of the two kinds of samples are investigated. The obtained results are as follows. 1) Comparing two samples, it is observed that more serious reverse-bias leakage current exists in the one with thicker superlattice;2) Room temperature electroluminescence (EL) measurement shows that the emission spectrum peak between two samples is blue-shifted to different extents as the injection current increases. With superlattice thickness increasing, the extent to which the peak is blue-shifted decreases. Nevertheless, there is no obvious discrepancy in the EL intensity between two samples with different thickness values at 300 K. In addition, the V-shaped pit characteristics including density and size, and the dislocation densities of two samples are studied by high-resolution X-ray diffraction, scanning electron microscope, and transmission electron microscope. The experimental data reveal that the reason for a tremendously different in reverse-bias leakage current between two samples is that there are larger and more V-pits in the superlattice sample with a large thickness. Whereas, V-pits also act as preferential paths for carriers, resulting in the fact that the thicker superlattice suffers more serious reverse-bias leakage current. According to reciprocal space X-ray diffraction intensity around the asymmetrical (105) for GaN measurement, the relaxed degree of InGaN quantum well on GaN is proportional to the superlattice thickness. On the other hand, it is useful for increasing superlattice thickness to reduce a huge stress in c-plane InGaN. Owing to joint effects of above factors, the EL intensities of the superlattice sample with different thickness values are almost identical. Our results show the functions of superlattice thickness in electronic and optical characteristics. What is more, the conclusions obtained in the present research indicate the practical significance for improving the performances of LED.
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