X-ray detector with thick epitaxial GaAs grown by chemical reaction

Thick (200 to 500 μm) epitaxial GaAs layers have been grown on two inch wafers by using a chemical reaction technique which is inexpensive, is nonpolluting, and allows very high growth rates. X-ray detectors made of p/i/n structures have been realized using nonintentionally doped layers grown on n⁺ GaAs substrates, with the p⁺ layer at the surface obtained by ion implantation. These detectors have been validated by current and capacitance-voltage measurements, photocurrent induced by X-ray irradiation, and energy resolution measurements. The data obtained demonstrate that these detectors exhibit similar performances as those obtained previously with conventional epigrowth techniques. Under standard conditions of medical examination (anode voltage of 60 kV, current of 75 mA, and distance of 70 cm), up to 10¹³ charges per second per mm² can be collected. The observed response time is apparently limited by the decay of the X-ray pulse.