A silicon photomultiplier detector cell may include a photodiode region and a readout circuit region formed on a same substrate. The photodiode region may include a first semiconductor layer exposed on a surface of the silicon photomultiplier detector cell and doped with first type impurities; a second semiconductor layer doped with second type impurities; and/or a first epitaxial layer between the first semiconductor layer and the second semiconductor layer. The first epitaxial layer may contact the first semiconductor layer and the second semiconductor layer. The first epitaxial layer may be doped with the first type impurities at a concentration lower than a concentration of the first type impurities of the first semiconductor layer.