An avalanche photodiode for detecting optical radiation, comprising:
- a substrate of a semiconductor material and having an upper major surface and a lower major surface;
- a first semiconductor layer having an upper major surface and a lower major surface and provided on the upper major surface of the substrate, said first semiconductor layer comprising a first group III-V compound semiconductor material doped to a first conductivity type and having a band gap corresponding to a wavelength of the optical radiation to be detected, said first semiconductor layer producing carriers in response to the optical radiation incident to the avalanche photodiode;
- a second semiconductor layer having an upper major surface and a lower major surface and provided on the upper major surface of the first semiconductor layer, said second semiconductor layer comprising a second group III-V compound semiconductor material doped to the first conductivity type and having a band gap substantially larger than the band gap of the first semiconductor layer, said second semiconductor layer being supplied with the carriers produced in the first semiconductor layer for causing an avalanche multiplication of the carriers;
- a photoreception region having an upper major surface a lower major surface and a lateral boundary and formed within the second semiconductor layer such that the upper major surface of the photoreception region coincides substantially with the upper major surface of the second semiconductor layer and such that the lower major surface of the photoreception region is located above the lower major surface of the second semiconductor layer, said lateral boundary connecting the upper major surface and the lower major surface of the photoreception region and extending to surround the photoreception region, said photoreception region comprising the second group III-V compound semiconductor material and doped to a second, opposite conductivity type and permitting passage of an optical beam incident to the avalanche photodiode, said lower boundary of the photoreception region forming a p-n junction between the photoreception region and the second semiconductor layer located underneath, said photoreception region having a first breakdown voltage;
- a guard ring region having an upper major surface and formed in the second semiconductor layer along the lateral boundary of the photoreception region and in continuation therewith such that the upper major surface of the guard ring region is adjacent to the upper major surface of the second semiconductor layer, said guard ring region comprising the second group III-V compound semiconductor material that is doped to the second conductivity type and surrounded by a boundary that has a protrusion toward the lower major surface of the second semiconductor layer, said guard ring region having a second breakdown voltage;
- a first electrode provided on the upper major surface of the guard ring region for making an electrical contact therewith;
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- a second electrode provided on the lower major surface of the substrate for making an electrical contact therewith;
- said first and second electrodes being adapted to be applied with a first polarity bias voltage and a second, opposite polarity bias voltage respectively, for applying a reverse bias voltage to the p-n junction formed at the lower major surface of the photoreception region and further for collecting the carriers that are formed in response to the optical radiation and the avalanche multiplication;
- said second semiconductor layer comprising a first material layer of the second group III-V compound semiconductor material having an upper major surface and a lower major surface adjacent to the lower major surface of the second semiconductor layer, a second material layer of the second group III-V compound semiconductor material having an upper major surface and a lower major surface and provided on the upper major surface of the first material layer, and a third material layer of the second group III-V compound semiconductor material and provided on the upper major surface of the second material layer such that the upper major surface of the third material layer is adjacent to the upper major surface of the second semiconductor layer, said first, second and third material layers having respective impurity concentration levels such that the impurity concentration level of the first material layer is substantially smaller than the impurity concentration level of the second material layer and the impurity concentration level of the third material layer is substantially smaller than the impurity concentration level of the second material layer;
- said photoreception region being formed such that the lower major surface of the photoreception region is adjacent to the lower major surface of the third material layer;
- the guard ring region being formed such that said protrusion has a lower edge extending to the vicinity of a boundary between the first material layer and the second material layer with a distance from the upper major surface of the first material layer set such that the second breakdown voltage becomes larger than the first breakdown voltage.