THE CHEMICAL ETCHING OF CdTe, ZnxCd1-xTe and CdxHg1-xTe SINGLE CRYSTALS WITH HNO3 – KI – DIMETHYLFORMAMIDE SOLUTIONS

Abstract

The chemical dissolution of CdTe single crystals, ZnxCd1-xTe and CdxHg1-xTe solid solutions in HNO3 – KI – dimethylformamide solutions has been investigated under reproducible hydrodynamic conditions for the first time. It is shown that the etching compositions of this system are cheaper, create a less aggressive environment, are more stable over time and are more ecologically safe. The diagrams «solution composition versus dissolution rate» has been plotted and the concentration limits of polishing etchant have been determined. Chemical-dynamic polishing with the investigated solutions can be carried out with a volume content of HNO3 9-15 %, while the polishing speed the surface of CdTe single crystals, ZnxCd1-xTe and CdxHg1-xTe solid solutions is within 1.6-2.5 μm/min. The dependence of the ions concentration that passed into the solution after the interaction of solid solutions ZnxCd1-xTe with the investigated etchants, versus the content of the oxidant in the etchant has been determined, and it was shown that the content of ions in the solution corresponds to the molar ratio in the semiconductor and indicates uniform dissolution of the surface. Based on the results of kinetic study, the apparent activation energy of the polishing was calculated for a solution of the composition (in vol. %): 12 НNO3 + 88 KI (DMF), which does not exceed 15.1 kJ/mol for СdTe and 7.7 kJ/mol for solid solutions on its basis, which indicates the limitation of the process by diffusion stages. The effect of the lactic acid and the nature of the semiconductors on the kinetics of chemical-mechanical polishing of the studied single crystals were determined. When the polishing solution is diluted with organic acid to 40 vol. %, the speed of chemical and mechanical polishing decreases from 3.5 to 0.5 μm/min. The compositions of etching mixtures and modes of implementation of chemical-dynamic polishing, which is recommended to be carried out in a suitable installation at the temperature 293 K and the disk rotation speed 82 min‑1, and chemical-mechanical polishing of the mention above semiconductor single crystals with the addition of lactic acid and polishing rates of 3.5-0.5 μm/min.