Depletion width equations...
The width of the depletion region d, is given by:
Practical detectors are almost always operated with a bias voltage that is very large compared to the contact potential, so that the applied voltage completely dominates the magnitude of the potential difference across the junction. In this situation:
In gamma-ray spectroscopy the active size of the detector (the depletion region) is always maximised by increasing the bias voltage so to extend the depletion region across the whole available detector volume.