SKM 2021 – scientific programme
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 4: Focus Session III: Diamond
KFM 4.5: Talk
Tuesday, September 28, 2021, 15:55–16:15, H2
Photoconductive gain in single crystal diamond detectors used for dosimetry — •Theodor Grünwald, Christina Bestele, and Matthias Schreck — Institut für Physik, Universität Augsburg, D-86135 Augsburg, Germany
Diamond crystals equipped with metal electrodes can be used for the detection of energetic radiation, i.e., x-rays, γ-rays and ionizing particles. Operated as solid state ionization chamber, single α-particles are completely stopped generating e-h pairs which can be collected with a maximum efficiency of ∼100%. When the same device is used as dosimeter in high intensity beams of energetic photons or particles, photoconductive gain G with values from <1 to >106 have been observed by various groups. This contribution analyzes first theoretically the irradiation induced conductivity of perfect diamond single crystals containing nitrogen and boron as electronically active defects. A system of coupled rate equations is formulated for the charging states of N and B, the concentration of electrons in the conduction band plus the neutrality condition. Analytical solutions are obtained for the gain as a function of the impurity concentrations, the detector thickness and the excitation density. The theoretical predictions cover the full range of experimentally derived values in literature. Photocurrent measurements on three series of heteroepitaxial samples grown under nearly identical conditions yielded G values ranging from <1 to >104. All the data are interpreted in terms of the measured absolute boron concentrations NB and the potential concentrations NN of nitrogen. In addition, the role of the dislocations as charge carrier traps is discussed.