Mapping sensitivity of CVD diamond detector using synchrotron micro-beam

Abstract

In this project, we conducted micro-beam sensitivity mapping using the Diamond Light Source (DLS) synchrotron. We fabricated three samples with distinct metal contacts: Platinum (HPS-Pt) and Aluminium/Platinum (HPS-Al/Pt) on high-quality single crystal CVD diamond, and Platinum (VS-Pt) on lower purity single crystal CVD diamond. Our objective was to identify the most suitable sample for synchrotron measurements, particularly focusing on the lower purity sample due to its unique characteristics, such as thin nitrogen lines and substrate area.

High spatial resolution sensitivity maps were obtained for the lower purity sample using a micro step displacement of up to 10 μm, revealing detailed nitrogen lines. We observed that bias polarity significantly influenced the photocurrent, with negative bias yielding higher photocurrents, possibly due to polarisation effects. Near nitrogen lines, we noted a slow rise time and an increased stabilization time with bias, alongside a prolonged decay to dark current.

For the HPS-Al/Pt sample, we found no improvement in current response homogeneity, therefore reliability, with bias; instead, we recorded high dark currents and unstable signals, particularly at negative bias. Conversely, the HPS-Pt sample exhibited a uniform response at both +50V and −50V in the central region of the sensitivity maps. This response became increasingly homogeneous at 100V and further improved up to 200V, suggesting that HPS-Pt is the most suitable candidate for synchrotron measurements.