Improvement in low-voltage performance of surface-electrode soft-X-ray detectors composed of undoped homoepitaxial CVD/HPHT Ib diamond layers

We have successfully fabricated diamond soft-X-ray (SXR) detectors with interdigitated surface electrodes that significantly improve the low-voltage performance using high-quality chemical-vapour-deposited (CVD) diamond films homoepitaxially grown on high-pressure/high-temperature-synthesised (HPHT) diamond Ib substrates. In the present study, the collection efficiencies of photon-excited carriers were evaluated using monochromatised SXRs at applied voltages ≤12 V for two types of diamond detectors with different stacking structures of the CVD layers. We found that the diamond detectors with an electrically floating B-doped layer sandwiched between two undoped CVD layers yield significantly larger carrier collection efficiencies compared to those without an inserted B-doped layer, even under the no-applied-voltage condition; moreover, the carrier collection efficiencies only slightly increase with increases in applied voltages below 12 V. This result indicates that the inserted B-doped layer can work independently (without electrical connection to any external circuit) as a potential barrier against carrier diffusions to a HPHT diamond substrate with much poorer quality than CVD diamond film of a photon absorption layer. The detector performances are discussed relative to the potential distribution formed in the active undoped diamond layer and the crystalline quality, which is based on the cathodoluminescence intensity of exciton emissions at room temperature.