Development of travelling heater method for growth of detector grade CdZnTe single crystals

We report on the indigenous design and development of laboratory scale travelling heater method (THM) system to grow detector grade Cd0.9Zn0.1Te (CdZnTe) single crystals. THM system mainly consists of two-zone furnace with a tuneable temperature gradient (30-80 degrees C/cm), high precision translation (1-25 mm/day) and rotation (1-50 rpm) assemblies to meet the stringent conditions that are essential to grow detector grade CdZnTe single crystals. Further, a load cell in the THM system enables continuous monitoring of the growth. Systematic growth experiments were performed to optimize the various growth parameters in order to achieve large grain single crystals. Herein, the effect of temperature gradient and growth rate on the increase in grain size is discussed in detail. Each successful growth experiment yields a minimum of four detector grade elements of dimensions 10 x 10 x 5 mm(3) from a starting charge of 100 g of CdZnTe. The crystalline nature and quality of the detector elements were evaluated using Laue, NIR transmission spectroscopy and I-V characteristics. Crystals with resistivity greater than similar to 10(9) - 10(10) Omega-cm were identified for testing gamma ray detection. The photo peak of Cs-137 was resolved with an energy resolution of 4.2% at 662 keV and its measured electron mobility lifetime product is found to be similar to 3.3 x 10(-3) cm(2)/V. The demonstration of the gamma ray detection with a relatively high mu tau product is the testimony to the successful growth of detector grade CdZnTe single crystals by an indigenously developed THM system.