the present invention relates to an avalanche photodiode having a simple structure , high reliability , and a high speed response on the order of gbps . this photodiode is formed by depositing laminated layers on a semiconductor substrate in the order of an n - type buffer layer , a semiconductor multiplication layer , a p - type semiconductor field buffer layer , a p - type semiconductor light absorbing layer , a p - type semiconductor cap layer , and a p - type semiconductor contact layer , and said p - type semiconductor light absorbing layer is constructed by two layers consisted of a depleted region of a thickness in the range of 10 nm to 0 . 3 μm disposed adjacent to the p - type semiconductor field buffer layer and a non - depleted layer region at a thickness of less than 2 μm disposed adjacent to the depleted layer region .