Epitaxial GaAs for X-ray imaging

To be used for X-ray imaging, semiconductor materials must exhibit good and uniform electronic properties. Epitaxial layers are therefore better adapted than bulk materials which contain dislocations, precipitates and point defects in variable concentrations depending on the growth mode and the nature of the material. However, they have to be thick enough to absorb photons efficiently. We produced thick epitaxial layers using a proprietary technique and made p/i/n (200–300 μm thick) diodes with this new material. These diodes are characterized by a large reverse current, which can originate from electron emission from deep level defects present in the depleted region or be a leakage current. In order to answer this question, we performed a characterization of the defects present in the material. Here, we describe results obtained from X-ray diffraction, X-ray topography, time resolved photoluminescence and resistivity measurements. We also investigated the possible effect of hydrogen. From these observations, we deduced that defects exhibiting an electrical role are in negligible concentration and concluded that the high reverse current observed is a leakage current.