Impurity and Te-Precipitate Reduction for Large Volume CdZnTe Single Crystal Growth

e goal of the project is to develop an advanced CdZnTe purification process to provide 8N purity or better starting material for large diameter CdZnTe boules for large volume CdZnTe single crystal substrate production for long wavelength infrared detector arrays. The 8N purity starting material will enable the growth of CdZnTe single crystals with significantly reduced concentration and size of Te precipitates in the substrates and the reduction of the concentration of micro defects in the HgCdTe films. We aim to significantly improve the purity of commercially available 7N purity CdZnTe by a purification technique employing the Traveling Heater Method (THM) and 7N purity Te solvent. The THM process is a very powerful purification process because most impurities tend to segregate into the Te solvent rather than to the CdZnTe boule. A factor of 5-10 impurity concentration reduction is possible with this technique. By repeated cycles of the THM process we aim to reduce the concentration of impurities from the current state-of-the-art of a few parts per billion (ppb) in the CdZnTe starting material. For the very low impurity levels required for 8N purity materials the standard chemical analysis technique of Glow Discharge Mass Spectrometry (GDMS) will not be sensitive enough to detect Cu and the other acceptor impurities such as Li, Na, Au, etc. To overcome the GDMS sensitivity limitation we propose to analyze the Te solvent purity rather than the CdZnTe boule purity. Because of the strong segregation of most impurities to the Te solvent significant accumulation of impurities will occur in the Te that will be above the detection limit of GDMS. By analyzing the Te solvent after each THM pass the trend of the CdZnTe ingot purification will be assessed. Approved for Public Release | 23-MDA-11635 (9 Nov 23)