The regularities of the physical-chemical interaction of the CdTe single crystals and ZnxCd1-xTe and СdxHg1-xTe solid solutions with aqueous solutions of the K2Cr2O7 – mineral acid – solvent systems have been established. For the first time, under the reproducible hydrodynamic conditions, the kinetic regularities of the dissolution process of a semiconductor single crystal surfaces in a liquid active medium have been determined using a rotating disc method. According to the results of experiments, using the method of mathematical simulation, 24 diagrams “solution composition – dissolution rate” of these materials in aqueous solutions of 6 systems (K2Cr2O7 – HBr – citric acid, K2Cr2O7 – HBr – oxalic acid, K2Cr2O7 – HBr – tartaric acid, K2Cr2O7 – HBr – acetic acid, K2Cr2O7 – HBr – lactic acid, K2Cr2O7 – HBr – ethylene glycol) were constructed, and concentration limits of solutions were found that exhibit polishing, selective or non-polishing effect on the surface of the semiconductors under study.
The influence of the organic components and the semiconductors on the rate and nature of the dissolution, as well as the condition of the treated surface CdTe, Zn0,04Cd0,96Te, Zn0,1Cd0,9Te and Cd0,2Hg0,8Tе were established. It is shown that during the polishing of ZnxCd1-xTe solid solutions using the developed etching compositions, the dissolution rate increases with increasing of Zn content, the boundaries of the areas of the polishing solutions widen, and the state of the polished surface improves. It has been found that with increasing mixing rate and etching temperature, the dissolution rate of single crystals increases. The value of the apparent activation energy of the dissolution process of these materials was calculated (Еа = 8.6-35.8 kJ/mol). According to the kinetic studies, the interaction of the semiconductor single crystals with polishing solutions is found to be limited by the diffusion stage. Constructing the dependence of the polishing rate on temperature helped to establish the existence of a compensating effect in the kinetics of chemical dissolution of СdTe, ZnxCd1-xTe and СdxHg1-xTe in the bromine-emerging solutions of the K2Cr2O7 – HBr – solvent systems. It has been found that it is influenced by the nature of the solutions used for chemical-dynamic polishing rather than semiconductor material.
The process of chemical-mechanical polishing of the surface of single crystals by etching compositions based on K2Cr2O7 was investigated. The effect of the modifier viscosity on the dissolution rate and the condition of the polished surface was determined. It was found that by introducing to the basic solutions of different amounts of tartaric acid, ethylene glycol or glycerol, the polishing rate of semiconductors can be adjusted and the etching solutions can be obtained with a wide range of dissolution rates (0.8-32 μm/min).
The morphology and surface composition of the semiconductors studied after dissolution have been investigated by the methods of atomic force microscopy and scanning electron microscopy. It is established that the chemical-dynamic and chemical-mechanical polishing using the developed etching compositions contributes to the formation of a super-smooth (Rа ≤ 10 nm), stoichiometric surface of single crystals.
A series of new slow etching compositions with a controlled dissolution rate (0.1-10.3 μm/min) have been developed, that allows them to be used to reduce the thickness of the plates to the specified sizes, to remove thin layers of material and to finish treatment of the single crystals surfaces.
Keywords: chemical dissolution, bromine emerging solutions, surface, solid solutions, etching, polishing, etching compositions.
