X-ray and γ-ray spectroscopy using a 2 x 2 GaAs p+-i-n+ diode array

A GaAs 2 x 2 pixel monolithic X-ray detector array was fabricated from material grown by metalorganic vapour phase epitaxy. Each pixel was a 200 mu m x 200 mu m square mesa p(+)-i-n(+) photodiode with a 10 mu m thick i layer. The array was electrically characterized and then each pixel was connected to the input of a custom-made, low noise, charge-sensitive preamplifier in turn Fe-55-X-ray,Cd-109 X-ray and gamma-ray, and Am-241 X-ray and gamma-ray spectra were accumulated at 20 degrees C. Following this, the spectroscopic response of one of the pixels was investigated at temperatures <= 100 degrees C. With both the preamplifier and detector array operated at 100 degrees C, the energy resolution (Full Width at Half Maximum) was 1.61 keV +/- 0.04 keV at 5.9 keV, 1.63 keV +/- 0.06 keV at 22.16 keV, and 1.65 keV +/- 0.08 keV at 59.54 keV. The results suggested that the pixels did not suffer from incomplete charge collection. The energy resolution achieved is the best reported so far for GaAs spectrometers at such high temperatures.