Abstract: A photodiode detector assembly for use with an ionizing radiation detector, the assembly includes a first layer having a first side and a second side and an array of backlit photodiodes disposed at the second side, and a second layer disposed proximate to and opposing the second side of the first layer. The second layer includes thru vias. Light rays entering the first layer at the first side and impinging the backlit photodiodes at the second side result in electrical signals at the thru vias of the second layer, thereby providing electrical output signals from the backlit photodiodes at a distance from the backlit photodiodes.