LED chip and preparation method thereof

The invention discloses an LED chip and a preparation method thereof. The LED chip sequentially comprises, from bottom to top, a substrate, a nucleation layer, a nitride buffer layer, a non-doped GaN layer, an N-type GaN layer, a multiple-quantum well layer, a P-type AlGaN layer, a P-type GaN layer, and a P-type InGaN contact layer. The LED chip further comprises a P electrode electrically connected with the P-type InGaN contact layer and an N electrode electrically connected with the N-type GaN layer, wherein the molar concentration of In in the P-type InGaN contact layer increases towards the direction away from the P-type GaN layer. According to the invention, the P-type InGaN contact layer is in contact with metal, the P-type InGaN contact layer is doped with high-concentration Mg, and the molar concentration of In is of a gradually-increasing gradient layer structure and peaks on the contact surface. The hole concentration of the P-type InGaN contact layer is high, the resistivity of contact between the P-type InGaN contact layer and metal is reduced, the possibility that carriers pass through metal and a semiconductor through tunneling to be in contact with a barrier region is improved, the work voltage of a high-power LED chip is reduced, light absorption is reduced, and therefore, the light emitting efficiency of the high-power LED chip is improved.