The International Axion Observatory (IAXO) aims to detect solar axions as they are back-converted into X-rays along a strong magnet pointing towards the sun. X-ray optics will concentrate the axion signal onto cm-scale ultra-low background detectors.  This detection could single-handedly resolve shortcomings in our description of strong interactions and represent the first observation of a dark matter candidate in a laboratory setting. 

As such axion signals will be rare, highly efficient X-ray detectors with a background performance similar to deep-underground experiments are required. Silicon drift detectors (SDDs) feature unique properties for this task. No structural components towards the telescope and only a very thin dead-layer allow for maximal X-ray absorption efficiency at solar axion energies. Construction from semiconductor grade materials and great freedom for sophisticated shielding strategies indicate great potential for ultra-low background applications.

BabyIAXO, the first stage of the IAXO program, is currently under construction at the Deutsches Elektronen-Synchrotron (DESY) in Hamburg. It will represent a testing ground for IAXO technologies, while probing unexplored axion parameter space. We aim to deploy a passively shielded SDD detector setup for this phase. For the even more challenging IAXO phase, we are developing a novel all-semiconductor active-shield X-ray detector, which consists of a single-pixel SDD operated inside a large-volume well-type high-purity germanium (HPGe) detector. This SDD-in-HPGe detector aims to achieve ultimate low-background performance for above-ground X-ray detection and boost the IAXO sensitivity to solar axions.