Development and optimization of the production technology of large-size position-sensitive detectors

Abstract

564Semiconductor nuclear radiation detectors, allow ing one to simultaneously determine the energies and locations of particle impacts have lately become irre placeable in studies of scattering processes on solid tar gets when determining the angular distributions of nuclear particles.Position sensitive detectors (PSDs) are being intensely developed for space, medical, and biological studies and for studies in atomic physics too. They have large advantages over other detectors of similar application, namely, the high energy and position res olutions; signal linearity in a wide energy range for particles of different types; insensitivity to magnetic fields; and stability, small overall dimensions, and arriving data processing simplicity.This work presents the results of our performed development and optimization of the production tech nology of semiconductor nuclear radiation PSDs, based on Si(Li) p-i-n large size X ray detectors for tomographic and ecological problems.The production of such detectors requires preci sion physical processes and conditions. They are spec ified by the fact that low energy X ray beams are applied in these systems for generation of electronhole pairs in the sensitive region of a semiconductor detector. The energy resolution in them should be E g < 200-300 eV, being almost limiting for many detectors based on semiconductor crystals. To meet the require ments for the energy resolution, it is necessary to cre ate physical conditions and mechanisms for ensuring the maximum collections of charge carriers, generated due to X ray quantum energy losses. In this case, these conditions should ensure the same result at any point of the sensitive region of the detector and the detector itself should be position sensitive.To solve these problems, it is required to correlate properties of the initial semiconductor crystal (con ductance, homogeneity, imperfection, etc.) and con ditions for providing high efficient p-n or p-i-n semiconductor structures with large sensitive region volumes and thin input windows ("dead layer") on the frontal side of the structure.The creation of Si(Li) p-i-n structures with a sen sitive region diameter of ~100-120 mm and a thick ness >1.5 mm is a technologically complex problem. In particular, it is necessary to create a sufficiently extended, uniformly lithium compensated sensitive region. To obtain the specified characteristics of the large size PSDs, such parameters as the temperature, diffusion annealing time, voltage values, and drift conduction method, are important. The diffusion and lithium ion drift modes are selected in accordance with those proposed in [1, 2].The lithium diffusion was performed in vacuum to a depth of ~500 µm at the temperature t = 500°C. After the diffusion, steps were etched on the plate to obtain a T shaped form. After etching by the polishing etchant in an HF : HNO 3 : CH 3 COOH (1 : 3 : 1) acid mixture and in the aniline etchant, the initial samples had reverse currents I ≤ 10 µA. Then, the lithium ion drift was carried out in samples on...