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Mercuric iodide single crystals have been grown by static and dynamic sublimation wthods. tics of contacts and detector capacitance have been studied by photon excitation methods. spectrometry has been carried out with completed detectors showing resolutions comparable to the best results published to date, length has been made from the spectral shapes observed and has been found to be approximately 0.3 mm. sient waveform analysis with alpha-particle excitation shows hole mobilities of approxinately 3 cmZ/V-sec for a highly purified crystal and 0.C5 for an expected less pure crystal. Electron mobilities of 120 cm2/V-sec are observed. An attempt is made to explain the observed transient waveforms in terms of a single dominant trap model, with only partial success. Due to the strongly excitonic character of the material, it is proposed that the unfamiliar observations made regarding transport properties with the Hg12 detectors studied may be due to exciton dissociation under high electric fields, to long exciton lifetimes and to interactions between excitons and trapping centers in the material. Characteris- Gamma and X-rayA measurement of hole trapping Tran- IntroductionThe feasibility of using mercuric iodide as a low energy gamma and X-ray spectrometer has been unequivocally demonstrated by Xald and by Swierkowski, Armantrout and Wichner,2 following initial work by Willig and Roth. 3 Substantial rcsGlution was achieved by irradiating the negative electrode of a detector so that electrons, found to be less r e a d i l y t r a p p e d t h a n holes, were responsible for mosr: o f the charge collec-'tion. cmz/V-sec with a limiting drift velocity of 6.5 x 105 cmlsec and a hole mobility of approximately 4 cmZ/V-sec. Relevvt physical constants and some trapping parameters for HgI2 are included in the first two referenced papers. I n an effort to develop as12 to its full capabilities as 2 radiation d,etector (i.e., not limited to low energy photons), a prcgram of purification, crystal growth and detector physics of HgIq has been initiated. In this paper, the first results o f studies on detector performance and carrier transport phenomena in crystals grown b v two somawhar differen: processes will be reported. X discussion on crystal growth nethods will also be given. Malm1 has reported an electron mcbility of 70From the detector ?hysics.point of view, it is expected that this paper will ra,ise some questions which are n o t readily answerable. It is strongly felt, however, that furti:er s o r k cn the subject will lead to clear indications on now best to carry out the purification, crystal prowtn ard detector.iabrica:ion steps for results beyond the ales that have. been zttained to date. N O T I C E The Excitonic Nature of HgI2Mercuric Iodide has received substantial attention in the literature of Physics on account of two of its characteristics: (1) high photoconductivity,4 and (2) the strongly excitonic nature o f its light absorption and emission characteristics.5-:~ In fact, the wellproven correlation be...