Fast X-ray detection systems based on GaAs diodes grown by LPE

We report on the fabrication and characterization of GaAs based X-ray detectors. The detector structures are grown by liquid phase epitaxy (LPE) and show typical background doping in the order of 10¹⁴ cm^-3 (n-type) so that active regions up to 43 μm could be realized. Schottky diodes were processed with active areas up to 1 mm². Typical dark current densities are as low as 360 pA/mm² at 100 V. The energy resolution of the detector in combination with a charge sensitive preamplifier was determined to be 1.6 keV (FWHM) for X-rays with an energy between 6 and 60 keV. The time response of the devices coupled to a fast transimpedance amplifier with a bandwidth of 100 MHz was investigated. Single photon detection at room temperature was achieved for X-rays having energies of 14 keV and higher. The measured time resolutions were 600 ps (FWHM=1.4 ns) and 430 ps (FWHM=1.0 ns) for X-ray photons of 14.4 keV and 21.5 keV, respectively. The efficiency of the detector having a 43 μm thick depleted layer was determined to be 70% at 14.4 keV and 40% at 21.5 keV. These detectors open a new field of X-ray spectroscopy especially for high rate applications and timing measurements at synchrotron radiation facilities