Disclosed herein is radiation detector, comprising a first photodiode comprising a first junction; and a first scintillator, wherein a first point in a first plane and inside the first scintillator is essentially completely surrounded in the first plane by an intersection of the first plane and the first junction. The first junction is a p-n junction, a p-i-n junction, a heterojunction, or a Schottky junction. The radiation detector further comprises a first reflector configured to guide essentially all photons emitted by the first scintillator into the first photodiode. The first scintillator is essentially completely enclosed by the first reflector and the first photodiode.