Enclosure effects on the internal field distribution in HPGe planar detectors

The electric field distribution in planar HPGe detectors is studied and the attention is drawn on the effects in the peripheral region. The detector is considered with its enclosure (encapsulation) and the leakage current through the detector channel is also taken into account. It is shown that electric field distortions appear. For typical sizes of the capsule and the detector current, a layer of few millimetres (up to 10) is found where the distortion is still significant. The effect depends strongly on the leakage current and is influenced somewhat less by the capsule sizes (the distance from the capsule wall and the germanium crystal) and the bias voltage.