An avalanche photo-transistor device (500, 600), the device comprising: a detection region (504, 604) configured to: absorb light incident on a first surface of the detection region; and generate one or more charge carriers in response to absorbing the incident light; a first terminal (530, 630) in electrical contact with the detection region (504, 604) and configured to bias the detection region (504, 604); an intermediate doping region (520, 620) having a doping concentration of a first type dopant that is greater than a threshold doping concentration, wherein the one or more charge carriers flow toward the intermediate doping region (520, 620); a second terminal (532, 632) in electrical contact with the intermediate doping region (520, 620) and configured to bias the intermediate doping region (520, 620); a multiplication region (516, 616) configured to: receive the one or more charge carriers flowing from the intermediate doping region (520, 620); and generate one or more additional charge carriers in response to receiving the one or more charge carriers; and a third terminal (534, 634) in electrical contact with the multiplication region (516, 616) and configured to bias the multiplication region (516, 616), wherein the intermediate doping region (520, 620) is located in between the detection region (504, 604) and the multiplication region (516, 616), characterized in that the avalanche photo-transistor device is a laterally-integrated avalanche photo-transistor device in which a flow of charge carriers generated within the detection region and of additional charge carriers generated within the multiplication region is lateral with respect to a light incident top surface of the device. a detection region (504, 604) configured to: absorb light incident on a first surface of the detection region; and generate one or more charge carriers in response to absorbing the incident light; absorb light incident on a first surface of the detection region; and generate one or more charge carriers in response to absorbing the incident light; a first terminal (530, 630) in electrical contact with the detection region (504, 604) and configured to bias the detection region (504, 604); an intermediate doping region (520, 620) having a doping concentration of a first type dopant that is greater than a threshold doping concentration, wherein the one or more charge carriers flow toward the intermediate doping region (520, 620); a second terminal (532, 632) in electrical contact with the intermediate doping region (520, 620) and configured to bias the intermediate doping region (520, 620); a multiplication region (516, 616) configured to: receive the one or more charge carriers flowing from the intermediate doping region (520, 620); and generate one or more additional charge carriers in response to receiving the one or more charge carriers; and receive the one or more charge carriers flowing from the intermediate doping region (520, 620); and generate one or more additional charge carriers in response to receiving the one or more charge carriers; and a third terminal (534, 634) in electrical contact with the multiplication region (516, 616) and configured to bias the multiplication region (516, 616), wherein the intermediate doping region (520, 620) is located in between the detection region (504, 604) and the multiplication region (516, 616), characterized in that the avalanche photo-transistor device is a laterally-integrated avalanche photo-transistor device in which a flow of charge carriers generated within the detection region and of additional charge carriers generated within the multiplication region is lateral with respect to a light incident top surface of the device.