A single-photon avalanche diode, SPAD, for use in a complementary metal-oxide-semiconductor, CMOS, integrated circuit and adapted for detection of light, such as visible or near infrared light, the SPAD comprising: a semiconductor substrate comprising a top surface at a front side and a back side opposite to the front side; an inner doped region (300, 410) disposed at a top surface of a semiconductor substrate connected to a first terminal, wherein a geometrical structure of a boundary of the inner doped region (300, 410) is rotationally symmetric in a horizontal direction of the semiconductor substrate and wherein the inner doped region (300, 410) comprises dopant implantations of a first type; at least one outer doped region (302, 420) disposed at a top surface of a semiconductor substrate connected to a second terminal, wherein the at least one outer doped region (302, 420) is arranged to at least partially enclose the inner doped region (300, 410) in the horizontal direction of the semiconductor substrate and wherein the outer doped region (302, 420) comprises dopant implantations of a second type; a lowly doped depletion volume (306, 430), which is arranged to surround the rotationally symmetric inner doped region (300, 410) and which comprises dopant implantations of the first type or dopant implantations of the second type; wherein a depth of the lowly doped depletion volume (306, 430) extending from the top surface of the semiconductor substrate into the semiconductor substrate is larger than a depth of the at least one outer doped region (302, 420), wherein the second terminal and the back side of the semiconductor substrate are commonly connected, and wherein one of the first and the second terminal forms an anode and another of the first and the second terminal forms a cathode, the anode and the cathode being separated by the lowly doped depletion volume (306, 430); wherein the SPAD is configured such that, when a reverse bias is applied to the anode, an electric field peak around the inner doped region (300, 410) is formed to enable impact ionization and multiplication of charges; and characterized in that II the inner doped region is small and a surface of the inner doped region (300, 410) at a doping transition to the lowly doped region (306, 430) is rotationally symmetric and contains no sharp corners, such that the electric field peak is spherically uniform around the first terminal and spaced away from the top surface. a semiconductor substrate comprising a top surface at a front side and a back side opposite to the front side; an inner doped region (300, 410) disposed at a top surface of a semiconductor substrate connected to a first terminal, wherein a geometrical structure of a boundary of the inner doped region (300, 410) is rotationally symmetric in a horizontal direction of the semiconductor substrate and wherein the inner doped region (300, 410) comprises dopant implantations of a first type; at least one outer doped region (302, 420) disposed at a top surface of a semiconductor substrate connected to a second terminal, wherein the at least one outer doped region (302, 420) is arranged to at least partially enclose the inner doped region (300, 410) in the horizontal direction of the semiconductor substrate and wherein the outer doped region (302, 420) comprises dopant implantations of a second type; a lowly doped depletion volume (306, 430), which is arranged to surround the rotationally symmetric inner doped region (300, 410) and which comprises dopant implantations of the first type or dopant implantations of the second type; wherein a depth of the lowly doped depletion volume (306, 430) extending from the top surface of the semiconductor substrate into the semiconductor substrate is larger than a depth of the at least one outer doped region (302, 420), wherein the second terminal and the back side of the semiconductor substrate are commonly connected, and wherein one of the first and the second terminal forms an anode and another of the first and the second terminal forms a cathode, the anode and the cathode being separated by the lowly doped depletion volume (306, 430); wherein the SPAD is configured such that, when a reverse bias is applied to the anode, an electric field peak around the inner doped region (300, 410) is formed to enable impact ionization and multiplication of charges; and characterized in that II the inner doped region is small and a surface of the inner doped region (300, 410) at a doping transition to the lowly doped region (306, 430) is rotationally symmetric and contains no sharp corners, such that the electric field peak is spherically uniform around the first terminal and spaced away from the top surface.