  The performance of a 630g commercial broad energy germanium (BEGe) detector
has been systematically investigated. Energy resolution, linearity, stability
vs. high-voltage (HV) bias, thickness and uniformity of dead layers have been
measured and found to be excellent. Special attention has been dedicated to the
study of the detector response as a function of bias HV. The nominal depletion
voltage being 3000V, the detector under investigation shows a peculiar behavior
for biases around 2000V: in a narrow range of about 100V the charge collection
is strongly reduced. The detector seems to be composed by two parts: a small
volume around the HV contact where charges are efficiently collected as at
higher voltage, and a large volume where charges are poorly collected. A
qualitative explanation of this behavior is presented. An event-by-event pulse
shape analysis based on A/E (maximum amplitude of the current pulse over the
total energy released in the detector) has been applied to events in different
energy regions and found very effective in rejecting non localized events. In
conclusion, BEGe detectors are excellent candidates for the second phase of
GERDA, an experiment devoted to neutrinoless double beta decay of Ge-76.
