III-nitride semiconductor visible light avalanche photodetector and preparation method thereof

The invention relates to a III-nitride semiconductor visible light avalanche photodetector and a preparation method thereof. The detector comprises a substrate and an epitaxial layer structure growingon the substrate. The growing sequence of the epitaxial layer structure from bottom to top is an unintentionally doped AlN buffer layer, an unintentionally doped AlxGa1-xN buffer layer, an n-type heavily doped AlyG1-yN ohmic contact layer, an Al composition gradient AlzGa1-zN polarization doped p-type layer, an unintentionally doped GaN multiplication layer, an n-type doped GaN charge layer, an InmGa1-mN/GaN superlattice light absorbing layer and an n-type heavily doped GaN ohmic contact layer. The detector adopts a p-type layer underlying structure, utilizes the piezoelectric polarization effect brought about by spontaneous polarization and compositional gradation in the AlGaN layer to generate three-dimensional hole gas to form the p-type layer without doping the acceptor impurity, andavoids the effect of the a