Study of the thickness of the dead Layer below electrodes, deposited by electroless technique, in CdTe nuclear detectors

The semiconductor nuclear detector structure is usually a superposition of several different layers: the metallic electrode, the interface, the depleted zone, the nondepleted one, and finally the second electrode. All inactive layers, and particularly the "dead layer" region below the metallic electrodes, give rise to absorption for photons (X, gamma) and to energy loss for charged particles. As a consequence, the detectors measure lower count rates for photons, particularly at low energies, and lower energies for charged particles. The amount of this effect can be only partially attributed to the inactive metallic electrode; the main part has to be attributed to the highly defected zone below the electrode in the interfacial region. This is a structural drawback which needs to be studied to reduce this effect, e.g., by developing new polishing and deposition techniques, or to perform the appropriate corrections. We have measured the thickness of this dead layer for various solution dilution electroless depositions of Pt electrodes on CdTe devices. These measurements were carried out by using collimated (X, gamma) rays beams impinging at different angles, especially the grazing ones, and comparing the count rates registered at two selected angles, and by measuring Rutherford backscattering spectra and energy loss of 4 He ions