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The carrier transport and recombination in light-emitting diodes(LEDs) determine the non-uniform intensity and distribution of the internal heat source.The non-uniform temperature field also influences the carrier transport and recombination in LEDs.Thus the carrier transport and recombination are strongly coupled with temperatures.In this paper,the internal quantum efficiency,spectrum characteristic and photoelectric conversion efficiency of LEDs with substrates of sapphire,Si and SiC are systematically studied by a non-isothermal multi-physics-field coupling model.It is shown that the LED with SiC substrate has the smallest efficiency droop effect and exhibits the highest spectrum intensity and photoelectric conversion efficiency,among the LEDs with substrates of sapphire,Si and SiC.This is because the LED with the substrate of SiC has the best thermal dissipation capability,thus the non-uniform temperature field has the smallest effect on the carrier transport and recombination,leading to the significantly enhanced carrier concentration in the active region and decreased current leakage.