Picosecond Photoconductors as Radiation Detectors

We have developed a new class of extremely high-speed radiation detectors. They are simple and inexpensive to fabricate, rugged, and reliable. We have demonstrated their sensitivity to gamma-rays, x-rays, soft x-rays, charged particles, and light and have obtained response speeds of <100 ps. Their current response is proportional to incident-radiation intensity. The detectors are not used for detecting single particles or measuring particle energy. Their current response is due to the modulation of the conductance of the semiconductor crystal by transientradiation events. The devices are fabricated from bulk-semiconductor crystals and achieve picosecond response by fast carrier relaxation in the crystals. Fast carrier relaxation is obtained by intentionally introducing trapping and recombination centers into the semiconductor crystal by impurity doping or radiation damage. Here we discuss the design, fabrication, and characterization of InP:Fe, GaAs, and neutron-damaged InP:Fe and GaAs photoconductive radiation detectors. We also present a model for transient response in InP:Fe photoconductors.