PbTe and Pb(1-x)SnxTe

PbTe and Pb(1–x)SnxTe - Wet Etching

Material Name: PbTe and Pb(1–x)SnxTe
Recipe No.: 10330
Primary Chemical Element in Material: Pb
Sample Type: Wafer
Uses: Etching
Etchant Name: None
Etching Method: Wet etching
Etchant (Electrolyte) Composition: For chemical etching, composition of etchant solution, its oxidative capacity, and rate of dissolution of interaction products are very essential factors. To select the optimal composition of etchants and research the kinetics of chemical etching of lead chalcogenides, there were performed preliminary studies of samples etching in acid and alkaline solutions with elementary I2 as oxidant. Lead chalcogenides are not dissolved in HCl and NaOH aqeous solutions in the absence of oxidant, which is probably caused by the nature of covalent chemical bonds in these compounds. Most of the investigated solutions acted on the samples surface at the dissolution forming thin layers or significant sediment, indicating that the rate of dissolution is limited by the etching of oxidation products. The surfaces of lead chalcogenides were clean and shiny only after their treatment in alkaline iodine solutions.

The kinetics of PbSe, PbTe and PbxSn1–x(Se,Te) solid solutions chemical etching in alkaline iodine solutions were investigated. The 0.015, 0.03, and 0.06 M iodine solutions in 12.5 M NaOH were used for experiments. The samples were preliminary polished with M 14 and M 7 powders and then etched in the mentioned etchant at 60 - 70 C. The surface state after etching was monitored with a MIM-7 metallographic microscope. The rate of PbSe and PbTe dissolution in these solutions versus temperature and iodine concentration changed within 10 exp(–9) - 10 exp(–10) mol/(cm2·s) and increased with mixture stirring. The etchant solution of 0.015 M I2 in 12.5 M NaOH was the most optimal concerning quality of surface obtained. The surface of PbTe becomes clean and bright after treatment by this etchant, and grain boundaries were exposed on the polished Pb(1–x)SnxTe surface.

An etchant containing NaOH (5 g), I2 (0.2 g), and H2O (10 ml) was also used for PbTe etching. The etching was performed on the PbTe (100) cleavage surface for 5 min under heating up to 95 C, there upon the wafers were washed with distilled water and carefully dried using filter paper. As a result of etching, pyramidal etching pits were formed on the samples surface.
As the solvents of elementary iodine can be used not only NaOH, but organic compounds and other substances, too. Practical meaning for being used in the etching compositions at the semiconductor surface is confirmed to such solvents of iodine as HI, KI and some others.
Solutions of I2 in methanol were used for the chemical-mechanical treatment of Pb(1–x)SnxTe solid solutions grown by the Czochralski method when forming the laser heterostructures. p-type samples with the carrier concentration close to 5 x 10 exp(16) cm(–3) and dislocation density 10 exp(7) cm(–2) were used for the experiments. Wafers of 6.0 × 6.0 × 0.4 mm in size and oriented in the direction (100) were polished with alumina powder and after that were etched in an iodine– methanol solution under stirring for 15 s. Chemical etching of the PbTe and Pb(1–x)SnxTe solid solutions single crystals were performed using the disk rotating method and iodine solution in dimethylformamide. The dependences of their etching rates versus etchant composition, temperature, stirring speed and the time of solution ageing were studied. The most reasonable application of solutions containing 6 to 18 wt.% of I2 in DMF is for formation of polishing etching compositions for PbTe and Pb0.83Sn0.17Te surface treatment.

Etchants based on bromine compounds (bromine-containing etchant solutions): The etchant containing 8 vol.% Br2 in HBr was used for chemical etching of PbxSn(1–x)Te. According to the data of Raman spectroscopy, formation of TeO2 and Te on the sample surface after chemical etching was observed. Under the subsequent treatment of the samples in boiling 50% NaOH solution and dilute HCl, only Te was detected on the surface. For chemical etching of the PbTe surface, a solution of Br2:HBr:H2O (volume ratio 1:40:40) can be also used.
Pb(1–x)SnxTe (100) wafers cut from Bridgman grown ingots were mechanically polished with the solution of 2% Br2 in ÍBr for removing residual lap damage before preferential etching to develop defects and pits. For polishing the PbTe crystals, the solution of 5 vol.% Br2 + 95 vol.% ÍBr was used. Etching was carried out for 1 min followed by treatment with 30% KOH (t ~40 C) for 20 min and washing by bidistilled water. Pb(1–x)SnxTe [100] wire-like crystals with the diameter from 10 to 60 mm were etched in the mixture containing 10 parts of the (5 vol.% Br2 + 95 vol.% ÍBr) solution and one part of toluene. Toluene contributes to the intensity of dissolution and eliminates formation of oxide film on the sample surface. Polishing was completed by thorough washing with acetone and then with deionized water. After that, the samples were immersed into a 10% HBr solution at the temperature 18-20 °C for 10 to 30 s. With a view to avoid formation of an oxide film, the samples were immediately subjected to contact nickel plating in a solution containing hydrobromic acid and nickel chloride.
Bromine-emerging etchants for chemicalmechanical and chemical-dynamic polishing PbTe and Pb1–xSnxTe single crystals: It was found that using the various concentrations of HBr (35, 40, 44, and 48%) in the etching compositions H2O2 x HBr does not substantially influence the etching rate of the PbTe and Pb(1-x)SnxTe crystal. However, the concentration range of polishing solutions was enlarged, and quality of polishing was improved when using more concentrated hydrobromic acid. It was shown that, for formation of the polishing etchants for the chemical-dynamic treatment, it is best to use 48% HBr; based on it etching compositions have average etching rates 1.0 to 17.0 µm/min and good polishing properties within the concentration range of 2 to 10 vol.% H2O2 in HBr. It was also developed a scheme of chemical surface treatment which includes cleaning the wafers with organic solvents, etching, and final washing in solutions that readily dissolve both residual etchant compositions and chemical reaction products.
Procedure (Condition): No data
Note: The review of works devoted to the use of polishing etchant composition for chemical treatment of the PbTe and Pb(1–x)SnxTe solid solutions single crystals and methods for their processing.
Reference: G.P. Malanych, Polishing etchant compositions for the chemical treatment of the PbTe and Pb(1–x)SnxTe solid solutions single crystals and methods for their processing. Review, Semiconductor Physics, Quantum Electronics & Optoelectronics, 2017. V. 20, N 2. P. 217-223. doi: https://doi.org/10.15407/spqeo20.02.217.