Solid state detectors use semiconducting crystals (in CRaTER's case, silicon) with n-type (electron-rich, electron conducting) and p-type (electron-deficient, hole conducting) sectors.

When a reversed bias voltage is applied at the p-type side, the unbonded electrons in the semiconductor are pushed away from the voltage source, while the holes are pulled towards it. This leaves a neutral area void of charge and current at the junction of the sectors, called the depletion region. As incoming radiation (eg gamma rays) collides with the depletion region, electron-hole pairs are formed in the material (where a once bonded electron is freed from its atom, leaving a hole). The electron and the hole respond to the applied voltage, and a small current is created. This current can be detected and later analyzed.

A cold environment greatly reduces the transmission of thermal signals. In addition, the solid state of the semiconducting material makes it easier to detect those signals attributable to freed electrons.