Melt growth and post‐grown annealing of semiinsulating (CdZn)Te by vertical gradient freeze method

Abstract

We present results of development of CdZnTe semi-insulating crystals prepared by Vertical Gradient Freeze method in a 4-zone furnace. We applied the way of growth of the crystal from the top when the first crystallization seed is created on the surface of the melt. The typical height of the crystals is 5 cm. Resistivity and photoconductivity profiles measured along the growth axis by contactless method are compared and their mutual correlation is explained based on a model of relative shift of the Fermi level and the midgap level present in the material. The influence of the Fermi level on electron trapping and recombination is summarized. We present here results of a two-step annealing method aimed at reduction of Te inclusions while keeping the resistivity high. We employed CdTe:Cl VGF grown samples to eliminate Te inclusions observed in as grown crystals by two-step post grown annealing in Cd and Te atmosphere and present a model of the processes leading to high resistivity material after annealing.

Growth of Single-Crystal Cd0.9Zn0.1Te Ingots Using Pressure Controlled Bridgman Method

“…HP-EDG provides CZT with low defect concentration, small inclusions, and electron mobility-lifetime product (µτ) e as large as 1 × 10 −2 cm 2 /(V•s) since evaporation of Cd during growth was strongly suppressed. Franc et al [9] grew four-inch diameter CZT single crystal wafers using the vertical gradient freezing (VGF) method, where a source with excess Cd was used and located below the seed in a slender ampoule cavity [10]. The temperature of the Cd source was held at approximately 830 • C in order to match the partial pressure of Cd in CZT.…”

Positron annihilation spectroscopy of vacancy-related defects in CdTe:Cl and CdZnTe:Ge at different stoichiometry deviations

“…Moreover a large mobility-lifetime product is desired to ensure that carriers generated by radiation in the whole detector volume can be collected by electrodes. Lattice defects form energy levels in the band gap and affect thereby the resistivity and the mobility lifetime product 9 . CdTe can be alloyed with Zn forming CdZnTe ternary compound.…”

“…The electric properties are affected by lattice defects forming energy levels in the band gap 9 . The determination of the properties of native defects and their complexes is particularly important to understand their role in crystal growth and compensating of extrinsic defects 4 .…”

Fundamentals and engineering of defects

“…They could be used to devise a related TQ(t) program. At the present, however, the stoichiometry is still corrected in cut wafers by postgrowth annealing, especially to minimize the precipitate density of the agglomerated excess component [29,30].…”