Gamma−ray spectroscopy with single−carrier collection in high−resistivity semiconductors

Abstract

With the standard plane−parallel configuration of semiconductor detectors, good γ−ray spectra can only be obtained when both electrons and holes are completely collected. We show by calculations (and experiments) that with contacts of hemispherical configuration one can obtain γ−ray spectra of adequate resolution and with signal heights of nearly full amplitude even when only one type of carrier is collected. Experiments with CdTe detectors for which the μτ product for electrons is about 103 times that of the holes confirm these calculations. The adoption of hemispherical contacts thus widens the range of high−resistivity semiconductors potentially acceptable for γ−ray detection at room temperature.

Three-Dimensional Position-Sensitive Germanium Detectors

“…For example, if the electron arrival occurs much sooner than the hole arrival, the interaction must have taken place near the x strips (Figure 7a), whereas if the opposite is true, the event must have occurred near the y strips ( Figure 7c). As a result of the small-electrode effect [32][33][34], the charge arrival at a strip electrode is marked by the rapid rise in the induced charge signal on that electrode. Consequently, the separate arrival times of the electrons and holes can be readily extracted and the time difference used as a measure of the depth of gamma-ray interaction.…”

Three-dimensional position sensing and field shaping in orthogonal-strip germanium gamma-ray detectors

“…The situation is different in the orthogonal-strip detector because of a small-electrode effect [14][15][16]. Consider a gamma-ray interaction event taking place near the center of the detector shown in Figure 1.…”

“…The depth of interaction in this detector is obtained from the difference in the arrival time of the holes at an electrode on one side of the detector and that of the electrons at an electrode on the opposing detector surface. This separate detection of the hole collection and the electron collection is fundamental to the technique and is facilitated by the small electrode effect [14][15][16] achieved with the strip electrodes.…”

<title>Position-sensitive germanium detectors for gamma-ray imaging and spectroscopy</title>

“…The extraction of these arrival times with an orthogonal-strip electrode geometry is facilitated by the small electrode effect. [16][17][18] Consider again the situation of a gamma-ray interaction event taking place near the center of the positive-biased detector. Under the influence of the applied bias, the generated carriers drift and separate.…”

“…14,15 The depth of interaction in these detectors is obtained from the difference in the arrival time of the holes at an electrode on one side of the detector and that of the electrons at an electrode on the opposing detector surface. This separate detection of the hole collection and the electron collection is fundamental to the technique and is aided by the small-electrode charge collection properties [16][17][18] achieved with the strip electrodes. The accurate measurement of the energy deposited by an interaction event in the detector is another critical requirement of these detectors.…”