Amorphous silicon, semiconductor X-ray converter detectors for protein crystallography

Hydrogenated amorphous silicon (a-Si:H) is a semiconductor material which can be inexpensively deposited to create a large array detector or readout structure. Combining it with a suitable semiconductor X-ray sensitive converter would produce a large, sensitive detector for X-rays with energies of 6–20 keV such as used in measurements of diffraction patterns for protein crystallography. In these experiments, the diffraction patterns created when X-rays strike crystallized protein samples are used to infer the physical structure of the molecules. The requirements for the detector include the ability to record signal peaks to high diffraction order to obtain accurate mapping of the electron density of the protein molecule, plus rapid sampling of the diffraction pattern to minimize radiation dose to the exposed crystal, while maintaining high signal-to-noise ratios. In this paper we summarize our results to date measuring and modeling the suitability of various semiconductor thin films for direct X-ray detection, and of the noise and readout properties of an amorphous silicon matrix array. We provide sample diffraction patterns obtained from a protein crystal taken at the Argonne Advanced Photon Source X-ray synchrotron using a phosphor coated a-Si: H array.