Hole density in non-depleted region of p-Si detector

In order to make useful detectors, which have high energy resolution and large sensitive area, we are going to develop detectors with p-type Si operated at low temperature (about 1 K). At 1 K, the w value of p-Si is 2 MeV. For the measurements of hole concentration, we have fabricated two types of devices: a single type device and a compound type device which consisted of two silicon wafers. The former type device is p-type silicon with 7 mm diameter and 0.5 mm thickness and 1013 cm-3 boron density. The latter type devices consisted of a silicon wafer with higher boron density (H-Si) and one with lower boron density (L-Si). Boron density of H-Si and L-Si were 3 x 1013 cm-3 and 8 x 1012 cm-3, respectively. From the results of single type device, holes were localized in non-depleted region by expanding depletion layer. The results of hole density measurement in compound type device showed that the hole density at 0 V was 1.24 X 1013 cm-3. This means that the holes in H-Si were forced into L-Si. At the condition of very low temperature, the resistivity of silicon becomes higher, so that higher density silicon can be used as H-Si. (S.Y.)