Mercuric iodine imaging detectors

Linear and two-dimensional monolithic arrays of different configurations have been fabricated using photolithographic techniques. The fabrication technology, electronic setup, and pinhole imaging experiments are described. Spatial resolutions of 1 to 2 mm have been achieved

Growth of single crystals of mercuric iodide (HgI/sub 2/) in spacelab III

Continued development of a system designed to grow crystals by physical vapor transport in the environment of Spacelab III will be described, with special emphasis on simulation of expected space conditions, adjustment of crystal growth parameters, and on board observation and control of the experiment by crew members and ground personnel. A critical factor in the use of mercuric iodide for semiconductor detectors of x-rays and gamma-rays is the crystalline quality of the material. The twofold purpose of the Spacelab III experiment is therefore to grow single crystals with superior electronic properties as an indirect result of the greatly reduced gravity field during the growth, and to obtain data which will lead to improved understanding of the vapor transport mechanism. The experiments planned to evaluate the space crystals, including gamma-ray diffractometry and measurements of stoichiometry, lattice dimensions, mechanical strength, luminescense, and detector performance are discussed

Low-temperature photoluminescence of detector-grade JgO/sub 2/

The low-temperature photoluminescence of HgI/sub 2/ is reported. Three main luminescence bands are observed, with peaks at approx. 2.30, 2.20, and 2.00 eV at 77K. At 4.2K, the highest energy peak shows considerable structure. The temperature dependence of these lines indicates both free and bound exciton recombination, and very small exciton binding energies (approx. 3 to 4 meV) have been estimated. A comparison of the results of sublimation and doping experiments suggests that the lowest energy band may be related to impurities, whereas the middle-energy band is related to I content. The two strongest bound exciton lines comprising the high-energy band show systematic correlations with the middle-energy, I- related band. Further correlations between these spectral features and the performance of nuclear radiation detectors fabricated from these samples are also noted. The temperature coefficient of the band gap is estimated from the spectral shift of luminescence lines to be approximately -1.13 x 10/sup -4/ eV/K between 32K and 45K

Place of HgI/sub 2/ energy-dispersive x-ray detectors

After a review of solid-state conduction counters, in general, and of the history of mercuric iodide, in particular, the theory of operation of solid-state energy-dispersive HgI/sub 2/ detectors is dicusssed. The main factors which limit energy resolution in solid-state compound detectors are considered, including statistical fluctuations in charge generation, the window effect, trapping, inhomogeneities in the detector material, and electronic noise. Potential applications of room-temperature HgI/sub 2/ x-ray detectors are listed, and general considerations are discussed for x-ray fluorescence analysis with HgI/sub 2/. Directions of current investigations are given. (LEW

Mobility and trapping time in HgI/sub 2/: a comparison of measurement methods and results

The charge transport parameters of a solid-state nuclear radiation detector are of paramount importance in determining the spectrometric performance. The free drift lengths (lambda) for electrons and holes are given in terms of the products of mobility (..mu..) and trapping time (tau) for electrons and holes. For good spectrometric performance the carrier free drift lengths should be much greater than the thickness of the detector. The ..mu.. tau product is so important in this regard that different solid-state detector materials are compared on the basis of their ..mu.. tau values, and for a given material progress is gauged by the current value of ..mu.. tau which it is possible to achieve. Workers in the field are fond of plotting ..mu.. tau versus time (in years, usually) to show how the state-of-the-art is advancing, often towards some asymptotic value. Different methods of measuring the charge transport parameters of mercuric iodide (HGI/sub 2/) are discussed and experimental values are presented. (WHK