Chao Xu, Juan Zhang, Changhe Zhou, Shangshu Li, Ruiyun Sun
National Key Laboratory of Infrared Detection Technologies, Shanghai Institute of Technical Physics of the Chinese Academy of Sciences, Shanghai 200080, PR China
## Abstract
CdZnTe (CZT) is the preferred material for HgCdTe (MCT) infrared detectors and room temperature nuclear-radiation detector applications. However, their widespread application is hindered by the low yield, attributed to intrinsic thermophysical properties like extremely low thermal conductivity and stacking fault energy, complicating the growth of large-volume crystals. Based on steady-state computer numerical modeling simulation, this paper examines the impact of seed size variations (from 15 mm to 90 mm) in the crystal growth process on the initial growth surface morphology, simulations indicate that larger seed crystals are predisposed to developing more convex interfaces, which are conducive to enhanced crystal growth. An optimized Vertical Gradient Freeze (VGF) method employing iso-diameter seed (having the same diameter as the grown crystals) of approximately 90 mm has been developed to grow single crystals with reduced defect density in a VGF furnace, and the applications in liquid phase epitaxy (LPE) are also discussed.
## Introduction
The progress in HgCdTe infrared technology [1], [2], [3] and radiation detectors [4], [5], [6] is heavily reliant on the quality of CZT crystals. Various methods have been developed for crystal growth, among which the Vertical Bridgman (VB) [7], [8], Vertical Gradient Freeze (VGF) [9], [10] and Traveling Heater Method (THM) [11] are the most commercially successful. Although some studies employing unseeded technologies [12], [13] have been reported, the prevalent use of seed crystals significantly improves the reproducibility of CdZnTe growth. Introducing a seed crystal reduces the randomness of spontaneous nucleation, creating a controlled environment essential for achieving consistent crystallographic orientation [14]. Due to the challenges and high costs of producing large-sized CZT seed crystals, researchers [15], [16] often opt for smaller seeds to grow CdZnTe single crystals. Additionally, some studies [17], [18]have explored the use of the THM for growing CZT crystals with iso-diameter seeds. And in the field of growing InP single crystals, 50 mm iso-diameter seed was used in the liquid-encapsulated vertical Bridgman technique [19]. However, achieving intact and defect-free single crystals remains a challenge, regardless of the seed size. The uniformity of the grown crystals, in terms of compositional homogeneity and defect distribution, requires further improvement to satisfy advanced detector application [20], [21]. Furthemore there is limited research on the impact of using seeds of different diameters in CZT growth. This study investigates the effect of seed crystal size on the growth interface with computer numeration simulation. The study also presents results for ∼ 90 mm diameter CZT single crystals grown using the VGF method with iso-diameter seed. Moreover, these crystals were processed into substrates, and the distribution of defects was characterized. Finally, the successful application of these crystals in the LPE process for HgCdTe was also reported.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/thesis/advancements-in-iso-diameter-seeded-growth-of-cdznte-crystals-a-numerical-modeling-approach-and-applications-in-liquid-phase-epitaxy.html