In this paper, the applicability of spark-source mass spectrographic analysis and SEM investigations for a-HgI2 is demonstrated. The influence of the chemical history of the material on the spectrum of the impurities has been investigated by comparing materials synthesized in three different ways. Static sublimation was used to grow single crystals, which had an appreciable average linear growth rate (10 -6 cm/sec) and relatively low etch pit density (103/cm 2 or less). Synthesis from "suprapur" elements after additional purification of iodine gave the most pure crystals, which still contained 1700 ppm at. of impurities. The spark source mass spectrographic analysis on ~-HgI2 reveals abundant distributions which are conspicuously characteristic of the crystal properties (valence, structure, composition, etc.) for elemental impurities, and crystal structure characteristic for the hydrocarbon fragments. Overall abundances for sublimated a-HgI2 vary according to the material source. Morphological investigation of uncoated crystal surfaces (as grown, etched, or cleaved) was possible by low temperature SEM investigation. They showed that most etch pits are flat bottomed at up to 10,000• magnification. Emergence points of dislocations are not visible; dislocations appear only in the form of a ~few pyramidal etch pits.Red tetragonal mercuric iodide (=-HgIz) has been receiving much attention as a material for roo.m temperature operable semiconductor detectors for low energy x-and -v-rays (1-3). This is due to its unique physical properties. Its wide bandgap of 2.1 eV, and the large atomic numbers of the components (80 for Hg and 53 for I) result in low dark current at room temperature and high photoionization efficiency (1, 2).Permanent address: The Graduate School at Nagatsuta, Tokyo Institute of Technology, Midori-Ku Jokohama 227, Japan.Key words: a-HgIe, single crystals by static sublimation, impurities in, mass spectrographic analysis of, SEM investigation on cold stage, spark source mass spectrographic analysis of HgIe, sublimation, static, of aHgI,~, vapor growth rate of a-HgI2 single crystals.A medical application was exemplified by a small HgI2 detector mounted inside an injection needle (4). Application to compute.r tomography is highly desirable if small size HgI2 detectors could replace the currently used large s,cintillation detectors. In this way, the local resolution of the tomograms would be improved.In the last six years, considerable progress has been made in crystal growth of ~-HgI2 and detector fabrication. However, the detector performance of HgI2 tends to suffer from insufficient collection of the electrons and holes, produced by the interaction of an incident photon with the crystal. This is due to rather
