The invention provides an epitaxial structure of a red and yellow GaAs
diode and a preparation method of the epitaxial structure. The epitaxial structure comprises a substrate, and a Bragg reflector, an N-type limiting layer, a multi-
quantum well layer, a P-type limiting layer, a P-type covering layer and a current expansion layer which are sequentially grown upwards on the substrate, wherein the Bragg reflector is of a periodic structure, Si
doping is carried out on the Bragg reflector, and the Si
doping concentration in the Bragg reflector is gradually increased along with increasing of the growth period of the Bragg reflector structure, so that the Bragg reflector has the function of an N-type covering layer. According to the invention, the epitaxial structure and the epitaxial
processing technology can be simplified, the production cost is lower, the Bragg reflector integrates the reflection effect of the Bragg reflector structure and the composite light-emitting
electron providing effect of the N-Cladding structure, and the light-emitting brightness of the
diode can be improved.