Development of the high-pressure electro-dynamic gradient crystal-growth technology for semi-insulating CdZnTe growth for radiation detector applications

The high-pressure electro-dynamic gradient (HP-EDG) crystal-growth technology has been recently developed and introduced at eV PRODUCTS to grow large-volume, semi-insulating (SI) CdZnTe single crystals for room-temperature x-ray and gamma-ray detector applications. The new HP growth technology significantly improves the downstream CdZnTe device-fabrication yield compared to earlier versions of the HP crystal-growth technology because of the improved structural and charge-transport properties of the CdZnTe ingots. The new state-of-the-art, HP-EDG crystal-growth systems offer exceptional flexibility and thermal and mechanical stability and allow the growth of high-purity CdZnTe ingots. 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 heat-transport modeling provides an excellent platform for continuing process development. Initial results on large-diameter (140 mm), SI Cd_1−xZn_xTe (x=0.1) ingots grown in low temperature gradients with the HP-EDG technique show reduced defect density and complete elimination of ingot cracking. The increased single-crystal yield combined with the improved charge transport allows the fabrication of large-volume, high-sensitivity, high energy-resolution detector devices at increased yield. The CdZnTe ingots grown to date produced large-volume crystals (≥1cm³) with electron mobility-lifetime product (μτ_e) in the (3–7) × 10⁻³ cm²/V range. The lower-than-desired charge-transport uniformity of the HP-EDG CdZnTe ingots is associated with the high density of Te inclusions formed in the ingots during crystallization. The latest process-development efforts show a reduction in the Te-inclusion density, an increase of the charge-transport uniformity, and improved energy resolution of the large-volume detectors fabricated from these crystals.