Position sensitivity in gallium arsenide radiation detectors

A study of the electrical response of detectors made from pure monolithic GaAs to MeV-energy alpha and proton radiation has been done as a function of the site of the ionization. A beam of particles was collimated to a diameter of 0.1 mm and swept across two detectors, one biased by a repeating pattern of electrodes on the front surface, the other a 1-mm cube biased between opposing faces with the electrical field normal to the beam. We found the charge response to single particles near the minus electrode to be three times larger than near the plus. The detector impulse response to subnanosecond pulses of protons restore quickly near the plus electrode, but near the minus, tails appear on the pulses that persist for over a half microsecond and dominate the net signal charge. A model based on electron detrapping is discussed, and a detector design is proposed