A radiation detector having a plurality of pixels is provided. A respective one of the plurality of pixels includes a thin film transistor on a base substrate; an inter-layer dielectric layer on a side of the thin film transistor away from the base substrate; a sensing electrode and a bias electrode on a side of the inter-layer dielectric layer away from the base substrate, wherein the sensing electrode extends through the inter-layer dielectric layer to electrically connect to the thin film transistor; a passivation layer on a side of the sensing electrode and the bias electrode away from the inter-layer dielectric layer, wherein the passivation layer includes a first portion and a second portion; and a radiation detection layer on a side of the passivation layer away from the base substrate. The first portion and the second portion form a substantially flat contacting surface.