Czochralski Growth of Indium Iodide and other Wide Bandgap Semiconductor Compounds

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Czochralski Growth of Indium Iodide and other Wide Bandgap Semiconductor Compounds I. Nicoara1, D.Nicoara1, C. Bertorello1, G.A. Slack1 and A. G. Ostrogorsky1, M. Groza2 and A. Burger2 1 Illinois Institute of Technology (IIT), Chicago, IL 60616 2 Fisk University, Physics Department, Nashville, TN 37208 ABSTRACT The Czochralski pulling process is the most valuable and cost efficient method for producing large oriented single crystals of the group IV and III-V semiconductors. However, there have been only a small number of reported attempts to use the Czochralski process for growing the wide bandgap compound semiconductors, needed for the room temperature operated gamma-ray detectors. The main difficulty is in the low chemical stability and high vapor pressure of the group II, V and VI elements, leading to off-stoichiometric composition, and various related defects. Among the heavy metal halides, indium iodide and indium bromide present an interesting exception. InI has a high molecular disassociation energy and a low vapor pressure, allowing for Czochralski pulling. We will describe the procedures used and the results obtained by Czochralski growth and characterization of indium iodide and the related ternary compounds that appear to be quite encouraging. INTRODUCTION The Czochralski crystal pulling, from the free surface of the melt, is the most valuable and cost efficient method for producing large oriented single crystals. The well established advantages of the Czochralski growth process include: i. The crystals grow and cool down unrestricted by the crucible walls. ii. Forced convection is easy to impose. iii. High throughput; large crystals can be obtained. iv. The growing crystal can be observed. The main drawbacks, compared to growth in sealed ampoules, are: a. The high vapor pressure materials have to be grown under liquid encapsulation using the Liquid Encapsulated Czochralski (LEC) process, or high inert gas pressure, in high pressure CZ pullers. b. The process requires continuous attention during seeding and necking c. For high melting point materials, temperature gradients are relatively high. So far, only B2O3 has proven to be a useful encapsulant used for LEC growth of the III-V arsenides and phosphides. There has been only a small number of attempts to use LEC for growing the wide bandgap II-VI compounds [1,2]. These later attempts have not been successful, because apparently, B2O3 reacts with the melt. Furthermore, the group II and VI elements are both volatile, making stoichiometry control difficult and leading to various related defects. A number of heavy metal iodides has been investigated as promising room temperature detector materials, because of their high density, stopping power, and useful energy band gap, Eg> 1.6 eV. These iodides include HgI2, PbI2, BiI3, InI, TlBr and TlI. Note that the heavy

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metal iodides are all are layered materials, with the exception of TlBr which has the cubic BCC structure. Yet, there is a significant difference between: (a) the di- and tri-valence halides, bu

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