CdZnTe crystals are largely employed as substrates for IR devices, X-ray detectors, and electro-optic modulators. One of the main problems affecting device quality is the presence of tellurium inclusions. These form during crystal cooling due to the retrograde shape of the liquidus curve or are incorporated during growth. In fact, the maximum melting point is actually on the Te side of the phase diagram. Moreover, high resistivity is obtained by doping with In or Cl and by growing  crystals from a Te-deviated charge.
Different approaches have been suggested for the elimination of tellurium inclusions by means of post growth treatments. One of them relies on the observation that when CdZnTe crystals are annealed in a temperature gradient, Te inclusions drift towards the higher temperature region, due to the fact that CdZnTe solubility in tellurium increases with temperature. However, it was reported by many authors that after thermal treatment high resistivity can’t be reproducibly recovered.
It was also shown that Te inclusions can experience thermomigration under the influence of a CO₂ laser irradiation at 10.6 micron [1]. The effect of the laser irradiation was evaluated comparing samples before and after irradiation.
In this work, we have studied the tellurium inclusion thermomigration induced by a pulsed Nd:YAG laser irradiation (1.064 micron). The inclusion movement was live-monitored in situ using our new IR microscopy system for 3D reconstruction of the position of  tellurium inclusions in CdZnTe crystals [2].
First of all, with respect to the use of the CO₂ laser, it should be noted that a much larger thermomigration speed was in general observed, without the need to heat the sample. Secondly, thanks to the in situ observation, it was possible to conclude that inclusions migrate at different speed according to their dimension. Moreover, inclusions separates into smaller parts and finally dissolve in the CdZnTe matrix.
In conclusion, it was shown that laser irradiation at 1.064 micron is a powerful method to eliminate tellurium inclusions from CdZnTe crystals without heating the sample and that thanks to live monitoring it is possible to study the thermomigration dynamics and, thus, to tailor the process at best.
[1] M. Meier, M. J. Harrison, S. Spalsbury, D. S. McGregor, “Laser-induced thermomigration of Te precipitates in CdZnTe crystals”, J. Crystal Growth 311 (2009) 4247-4250
[2] N. Zambelli, L. Marchini, M. Zha, A. Zappettini, “Three-dimensional mapping of tellurium inclusions in CdZnTe crystals by means of improved optical microscopy”, J. Crystal Growth 318 (2011) 1167-1170

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