Advances in the high-pressure crystal growth technology of semi-insulating CdZnTe for radiation detector applications

Abstract

The properties of large diameter (140 mm) semi-insulating Cd 1-x Zn x Te (x = 0.1) ingots grown by the vertical High-Pressure Electro-Dynamic Gradient (HP EDG) technique are discussed. The HP EDG crystal growth technology recently developed and introduced at eV PRODUCTS significantly improves the downstream CdZnTe detector fabrication yield compared to earlier versions of the HP crystal growth technology. These yield improvements stem from the improved structural and charge transport properties of the HP EDG CdZnTe ingots. Improvements were achieved in three areas: a) reduced thermal stress in the ingots, b) improved single crystal yield, and c) improved electron transport properties. The new state-of-the-art HP EDG crystal growth systems offer exceptional flexibility, thermal and mechanical stability and allow the growth of high purity CdZnTe materials. The flexibility of the multi-zone heater system allows the dynamic control of heat flow to optimize the growth-interface shape during crystallization. This flexibility combined with an advanced control system, improved system diagnostics and realistic thermal modeling provides an excellent platform for further process development. Results on the initial HP EDG CdZnTe ingots grown with low temperature gradient show the complete elimination of ingot cracking. The increased single crystal yield combined with the improved electron transport properties allows the fabrication of largevolume electron-only devices at higher yield. The CdZnTe ingots regularly contain sections with electron mobility-lifetime product e 5.0 10 -3 cm 2 /V and occasionally yield material with e 8.0 10 -3 cm 2 /V.

Electron backscatter diffraction analysis of a CZT growth tip from a vertical gradient freeze furnace

“…The authors used a model of two major defects, Cd vacancy (V Cd ) and Cd interstitial (i Cd ), to show that a very small deviation of P Cd from P S (the stoichiometry line in the P-T diagram at which the lattice defects were mutually compensated and the anion and cation atomic fraction relation x Cd +x Zn ¼x Te ¼0.5 was fulfilled) resulted in a large generation of the native defects. High-pressure Bridgeman (HPB) [3], highpressure electrodynamic gradient (HP EDG) [4,5], and containment crucibles (graphite vs. carbon-coated quartz) [6] showed improvements in the crystal quality and detector performance. Recently, Szeles [7] reviewed common bulk, interface, and surface defects and their effects on charge transport, charge transport uniformity, and device performance.…”

Research on the Technological Progress of CZT Array Detectors

“…The HPGF method incorporated multi-segment temperature control and furnace temperature field improvements, successfully eliminating cracks. However, crystals grown by this method still exhibited polycrystalline and twinning phenomena, resulting in lower utilization [20][21][22][23].…”