Dark matter detection

A summary is presented of the present status of several compound semiconductor radiation detectors, including detectors fabricated from GaAs, HgI2, CdTe, Cd1−xZnxTe and PbI2

Room-temperature compound semiconductor radiation detectors

State of the art of (Cd,Zn)Te as gamma detector

The first phase of a study of GaAs as a base material for solid-state detectors has been completed. The main motivation behind this study is the greater radiation resistance of integrated circuits made of GaAs (compared with Si). Many diodes, of different sizes and shapes but built with the same technique, have been tested electrically and as detectors, using α sources and minimum-ionizing particles. The tests show that these devices work with a full detection effeciency, although there is evidence for trapping of a fraction of the charge produced by the particle inside the semiconductor.

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A preliminary study of GaAs solid-state detectors for high-energy physics

In recent papers, we have investigated, within the context of the RD-8 experiment, the behaviour as a function of bias of the active region of particle detectors made by Alenia SpA on semi-insulating liquid encapsulated Czochralski gallium arsenide: the active region width depends linearly on the bias voltage. The diodes were found to break down as soon as the field reached the back ohmic contact. This suggested that the ohmic contact was injecting holes into the diode, therefore we have decided to develop a new, non-injecting, non-alloyed ohmic contact. This new contact allows us to go far beyond, five times, the voltage bias necessary to have a fully active detector. The higher voltage reached by the detectors helps us improve the charge collection efficiency, up to more than 95% for alphas and more than 90% for beta (mips) particles and X-rays, giving a more stable operation of the detectors. For the first time we can explore the characteristics of a GaAs detector beyond the voltage needed for it to be completely active.

Performance of a new ohmic contact for GaAs particle detectors

A review is given of room temperature semiconductors used as nuclear radiation detectors including GaAs, CdTe and HgI2. Some new applications are described in the field of dosimetry, spectroscopy and gamma or X-ray imaging.

Some new developments in the field of high atomic number materials

Operating as a photoconductor, the sensitivity and the impulse response of semi-insulating materials greatly depend on the excitation duration to electron compared and hole lifetimes. The requirement of ohmic contact is shortly discussed. Before developing picosecond measurements with an integrated autocorrelation system, this paper explains high energy industrial tomographic applications with large CdTe detectors (25 × 15 × 0.9 mm3). The excitation is typically in the μs range. X-ray flash radiography, with a 10 ns burst, is in an intermediate time domain where the excitation is similar to the electron lifetime. In laser fusion experiments excitation is in the 50 ps range and we develop photoconductive devices able to study very high speed X-ray emission time behaviour. Thin polycrystalline MOCVD CdTe films with picosecond response are suitable to perform optical correlation measurements of single shot pulses with a very large bandwidth (∼ 50 GHz).

Marc Cuzin

Papers

Some new developments in the field of high atomic number materials

CdTe in photoconductive applications fast detector for metrology and X-ray imaging