Simulation, Modeling, and Crystal Growth of Cd 0.9 Zn 0.1 Te for Nuclear Spectrometers KRISHNA C. MANDAL, 1,5 SUNG HOON KANG, 1 MICHAEL CHOI, 1 JOB BELLO, 1 LILI ZHENG, 2 HUI ZHANG, 2 MICHAEL GROZA, 3 UTPAL N. ROY, 3 ARNOLD BURGER, 3 GERALD E. JELLISON, 4 DAVID E. HOLCOMB, 4 GOMEZ W. WRIGHT, 4 and JOSEPH A. WILLIAMS 4 1.—EIC Laboratories, Inc., 111 Downey Street, Norwood, MA 02062. 2.—Department of Mechanical Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794. 3.—Center of Excellence in Physics and Chemistry of Materials, Fisk University, Nashville, TN 37208. 4.—Oak Ridge National Laboratory, Oak Ridge, TN 37831. 5.—E-mail address: kmandal@ eiclabs.com High-quality, large (10 cm long and 2.5 cm diameter), nuclear spectrometer grade Cd 0.9 Zn 0.1 Te (CZT) single crystals have been grown by a controlled vertical Bridgman technique using in-house zone refined precursor materials (Cd, Zn, and Te). A state-of-the-art computer model, multizone adaptive scheme for transport and phase-change processes (MASTRAP), is used to model heat and mass transfer in the Bridgman growth system and to predict the stress distribution in the as-grown CZT crystal and optimize the thermal profile. The model accounts for heat transfer in the multiphase system, con- vection in the melt, and interface dynamics. The grown semi-insulating (SI) CZT crystals have demonstrated promising results for high-resolution room- temperature radiation detectors due to their high dark resistivity (r  2.8 3 10 11 V cm), good charge-transport properties [electron and hole mobility-life- time product, mt e  (2–5) 3 10 ÿ3 and mt h  (3–5) 3 10 ÿ5 respectively, and low cost of production. Spectroscopic ellipsometry and optical transmission mea- surements were carried out on the grown CZT crystals using two-modulator generalized ellipsometry (2-MGE). The refractive index n and extinction coef- ficient k were determined by mathematically eliminating the ;3-nm surface roughness layer. Nuclear detection measurements on the single-element CZT detectors with 241 Am and 137 Cs clearly detected 59.6 and 662 keV energies with energy resolution (FWHM) of 2.4 keV (4.0%) and 9.2 keV (1.4%), respectively. Key words: CZT, MASTRAP model, Bridgman technique, 2-MGE, radi- ation detectors INTRODUCTION Cadmium zinc telluride (CZT) has emerged as one of the most attractive and promising materials for room-temperature g- and x-ray spectroscopy. CZT material has the advantages of high average atomic number (Z  50), high density (5.8 g/cm 3 ), and wide bandgap (.1.50 eV at 300 K), yielding CZT detec- tors that are highly efficient at room temperature and above. 1 Currently used Si and Ge detectors can only work efficiently at liquid-nitrogen tempera- ture, which is expensive and inconvenient. The energy required for generating one electron-hole pair in CZT (;5 eV) is much less than that required for scintillation crystals coupled to photomultiplier tubes (;50 eV), resulting in better energy resolu- tion. CZT materials also have shown improved spec- tral performance using novel, single-carrier detector designs, such as a Frisch ring, 2,3 small pixel effect, 4 and coplanar grid. 5 Due to these advantages, CZT has been the material of choice for x- and g-ray detectors for medical imaging, infrared focal plane array, national security, environmental monitoring, and space astronomy. 6–9 (Received October 17, 2005; accepted December 14, 2005) Journal of ELECTRONIC MATERIALS, Vol. 35, No. 6, 2006 Special Issue Paper 1251