X-ray detector based on GaN

The potential of GaN for X-ray detection in the range from 5 to 40 keV has been assessed. The absorption coefficient has been measured as a fonction of photon energy. Various detectors have been fabricated including MSM and Schottky diodes. They were tested under polychromatic X-ray illumination and under monochromatic irradiation from 6 to 22 keV in the Soleil synchrotron facility. The vertical Schottky diodes perform better as their geometry is better suited to the thick layers required by the low absorption coefficient. The operation mode is discussed in terms of photoconductive and photovoltaic behaviors. Some parasitic effects related to the electrical activation of defects by high energy photons and to the tunnel effect in lightly doped Schottky diodes have been evidenced. These effects disappear in diodes where the doping profile has been optimized. The spectral response is found to be very consistent with the spectral absorption coefficient. The sensitivity of GaN Schottky diodes is evaluated and found to be on the order of 40 photons per second. The response is fast nd linear.