Red light LED epitaxial structure, LED chip and preparation method thereof

The invention discloses a red light LED epitaxial structure, an LED chip and a preparation method thereof, the red light LED epitaxial structure has a composite DBR structure, and the method comprises the following steps: growing m groups of Al < x > Ga < 1-x > As/Al < As > above a GaAs-Si buffer layer; and then growing n groups of Al < 0.5 > Ga < 0.5 > As/AlAs to form a double-layer composite DBR structure. The composite DBR structure is used for replacing an original DBR structure, the new structure increases the reflectivity difference value of AlGaAs and AlAs, the light emitting efficiency of the normal LED can be improved, high light output can be achieved under low current, compared with a flip chip, cost can be reduced, the voltage application range is wide, stable light emitting performance can be kept under different voltage conditions, and the light emitting efficiency of the normal LED can be improved. The product yield is improved, the structural design is compact, the LED light source can be conv