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In this study, we have systematically investigated the effect of Si doping level in the n-cladding layer on the performance of InGaN/GaN-based light-emitting diodes (LEDs). Detailed structural, optical and electrical properties of the sample with different Si doping level were studied. Based on these investigations, it was found that with a low level of Si doping (0.738 nmol/min, ~ 5.4×1017 cm3), the subsequent multiple-quantum-well (MQW) structure showed superior crystalline quality with low-density threading dislocations (TDs); however, the operation voltage of the LED chips became unbearable. On the other hand, the highly-doped (14.40 nmol/min, ~ 1.1×1019 cm3) samples showed a substantially lower operation voltage, but the MQW quality deteriorated with much higher TD density. Finally, the effect of inserting a 100-nm-thick undoped spacer GaN layer between the n-cladding layer and active layers was also investigated. The electrical and emission properties both deteriorated while the crystalline quality improved for LEDs with this structure, proving the importance of electron injection on the performance of LEDs.