Because of thermic energy and repulsion due to the electric fields inside such a device, the charge cloud diffuses, effectively getting larger in lateral size.
[2] Furthermore, fluorescence of the detector material above its K-edge can lead to additional charge carriers that add to the effect of charge-sharing.
If a certain part of the charge cloud is diffusing to the read-out electronics of a neighbouring pixel, this results in the detection of two events with lower energy than the primary photon.
The registration of one incident photon in several pixels degrades spatial resolution, as the information about the primary interaction is smeared out.
Other correction approaches basically rely on a deconvolution in the signal domain, taking calibrated detector response into account.