The Response Of An Hyperpure Germanium Detector To Ionizing Radiation

A basic understanding of the response of semiconductor detectors to ionizing radiation is important for their proper usage and their further development. Such devices may also be used to explore the energy deposition process in semiconductors.;The detailed response of an HPGe detector ({dollar}\sim{dollar}1 cm{dollar}\sp3{dollar} hyperpure Ge with an ion-implanted front contact) to ionizing radiation has been studied with regard to the radiation ionization energy ratio, {dollar}\varepsilon\sb{lcub}\rm ion{rcub}{dollar}/{dollar}\varepsilon\sb0{dollar}, using radioactive {dollar}\alpha{dollar} and {dollar}\gamma{dollar} sources and accelerated ion beams ({dollar}\sp1{dollar}H, {dollar}\sp{lcub}3,4{rcub}{dollar}He, {dollar}\sp7{dollar}Li). The data span the energy range of a few hundred keV to a few MeV. Effects of temperature and bias voltage variation have been investigated. The response to charged particles and {dollar}\gamma{dollar}-rays have been measured simultaneously by using {dollar}\sp{lcub}152{rcub}{dollar}Eu, {dollar}\sp{lcub}60{rcub}{dollar}Co, and {dollar}\sp{lcub}137{rcub}{dollar}Cs {dollar}\gamma{dollar}-ray sources.;Analysis of the results reveals: (1) Contrary to earlier conclusions, a difference of {dollar}\sim{dollar}1% between {dollar}\varepsilon\sb0{dollar} and {dollar}\varepsilon\sb{lcub}\rm\alpha\ or\ p{rcub}{dollar} has been found in Ge, often showing {dollar}\varepsilon\sb{lcub}\rm\alpha,p{rcub}\u3c\varepsilon\sb0{dollar}--results that are qualitatively in accord with the observed behaviour for Si semiconductor detectors; these observations cannot be explained by trapping or recombination effects during the stopping of the ion in the sensitive volume. (2) The functional behaviour of {dollar}\varepsilon\sb\alpha{dollar}/{dollar}\varepsilon\sb0{dollar} and {dollar}\varepsilon\sb{lcub}\rm p{rcub}{dollar}/{dollar}\varepsilon\sb0{dollar} exhibits a non-linear response of the Ge detector as a function of ion energy for a given projectile, which is similar to results observed for Si detectors; the ratios approach unity as the particle energy increases--a result that is to be expected from fundamental considerations. (3) Where comparisons can be made with earlier works, the present results for {dollar}\varepsilon\sb{lcub}\rm ion{rcub}{dollar}/{dollar}\varepsilon\sb0{dollar} are in good quantitative agreement when similar assumptions are included, e.g. the apparent window thickness of the Ge detector is assumed to be independent of ion energy. (4) The energy loss in the window of the Ge detector is found to vary with the energy of the incident particle in a manner that does not agree with the stopping power curve. The apparent thickness of this window region is observed to decrease dramatically with increasing detector temperature ({dollar}\sim{dollar}30% decrease as T increases from 80K to 175K). This observation suggests that the surface layer of the Ge detector does not consist of a simple passive dead layer. The reasons for this behaviour are not presently understood. (5) Pronounced channeling effects are evident in the pulse height spectra as the incidence angle of the ions is rotated with respect to the detector surface normal. These features arise from ion channeling effects in the ion-implanted entrance window region. Monte Carlo calculations of the projectile energy loss under channeling conditions are in qualitative agreement with experimental observations. However, such channeling effects do not account for the deviations of {dollar}\varepsilon\sb{lcub}\rm ion{rcub}{dollar}/{dollar}\varepsilon\sb0{dollar} from unity