A surface etching method for revealing dislocation defects of tellurium-indium-lead single crystal

Abstract

A surface etching method for revealing dislocation defects of tellurium indium lead single crystal, which relates to a method for revealing crystal defects. It is to provide a surface etching method which can accurately reveal crystal defects. The method: first, the PIT single crystal is cut, multi-stage mechanical polishing and chemical mechanical polishing to obtain a smooth and undamaged surface; then, iodine reacts with concentrated nitric acid to generate iodate as the main oxidant, hydrogen fluoride is added to activate and diluted with acetic acid-water mixture, and the crystal is etched at low temperature of 10±1 DEG C and under ultrasonic assistance. The method can form regular triangular pyramidal etch pits on the (001) surface of the PIT single crystal, the depth is 100-300 nm, the pit bottom points to the [001] direction, and the dislocation defects are clearly revealed. The method has the advantages of clear etching morphology, high sensitivity, strong reliability and simple operation, and can be used in the fields of PIT single crystal quality evaluation, defect analysis and growth process optimization.

Description

Technical Field

[0001] This invention relates to a method for etching single crystals of lead indium telluride. Background Technology

[0002] Infrared nonlinear optical crystals have demonstrated significant application value in key fields such as industry, medicine, and energy. However, currently commercially available chalcopyrite-based infrared crystals (such as AgGaS2, AgGaSe2, and ZnGeP2) generally suffer from intrinsic defects such as low laser damage threshold and two-photon absorption, severely limiting their practical application in far-infrared high-power solid-state lasers. To meet the development needs of modern infrared laser technology, it is urgent to develop novel crystal materials with the following characteristics: firstly, the ability to efficiently utilize the 1064 nm pump laser output from Nd:YAG lasers; and secondly, an output wavelength range covering more than 10 μm. Compared to phosphorus compounds, telluride crystals among chalcogenides have a significant advantage in achieving a wide infrared transmission range (especially covering the 10~14 μm atmospheric window) due to their lower phonon energy. Among them, the ternary telluride PbIn6Te... 10 Piezoresistive indices (PIT) have attracted considerable attention as a novel nonlinear optical crystal material. PIT crystals belong to the trigonal crystal system with space group R32 and possess excellent comprehensive properties: wide transmission band (1.3 ~ 31 μm), moderate birefringence (~0.05), and a large nonlinear optical coefficient (d). 11 = 51 pm / V). Theoretical simulations and experimental studies (such as the achievement of 5 ~ 25 μm tunable laser output using 2 μm laser pump light parametric oscillation technology) both demonstrate that PIT crystals have great potential to achieve 10 ~ 30 μm laser output.

[0003] However, PIT single crystals grown using existing methods generally suffer from severe cracking, strong optical absorption, and uneven elemental distribution within the crystal. The root cause lies in the fact that PIT, as a heterogeneous melting compound, presents significant challenges in precisely controlling the melt composition during single crystal growth, leading to the formation of structural defects such as dislocations and inclusions within the crystal. These defects are the direct cause of crystal cracking, deterioration of optical properties, and uneven elemental distribution, severely hindering the full realization of PIT crystal performance and its practical applications. Currently, there is no method to directly detect crystal defects. Therefore, while optimizing crystal growth, it is urgent to develop a method that can effectively and intuitively characterize the internal structural defects (especially dislocations) of PIT single crystals to gain a deeper understanding of defect formation, guide improvements in growth processes, and screen for high-quality crystals. Summary of the Invention

[0004] To overcome the performance degradation problem caused by dislocation defects in PIT single crystals in existing technologies, this invention provides a surface etching method that can accurately reveal crystal defects. To achieve this goal, the PIT single crystal surface must first be pretreated to construct a damage-free crystal surface as the basis for defect characterization. This ensures that the subsequent etching process selectively responds only to intrinsic defects within the crystal. By effectively and intuitively characterizing the internal structural defects (especially dislocations) of PIT single crystals through etching technology, a deeper understanding of defect formation can be achieved, guiding improvements in growth processes and the selection of high-quality crystals.

[0005] The present invention discloses a surface etching method for revealing dislocation defects in a lead indium telluride single crystal, comprising the following steps:

[0006] I. On PbIn6Te 10 (PIT) single crystals undergo pretreatment:

[0007] (1) Use an X-ray crystallography instrument to determine the crystal orientation, cut along the target crystal plane to obtain a wafer;

[0008] (2) Use micron-sized to submicron-sized abrasives in sequence, and use multi-level gradient mechanical polishing to gradually reduce the surface roughness, while using ultrasonic cleaning to remove abrasive residues.

[0009] (3) Using alkaline colloidal polishing solution, chemical mechanical polishing is used to eliminate the subsurface damage layer and obtain crystals with smooth and flat surfaces;

[0010] (4) The crystal surface is then subjected to organic solvent degreasing, dilute acid solution deoxide removal, high-purity water multi-frequency ultrasonic rinsing, and finally inert gas purging and low-temperature vacuum drying to obtain a crystal with a clean hydrophobic surface; before the etching process, PbIn6Te is ... 10 (PIT) single crystals undergo systematic pretreatment to ensure surface integrity. This pretreatment step effectively eliminates microcracks caused by mechanical stress and surface adsorbed impurities, providing a non-damaging substrate for subsequent accurate exposure of crystal defects.

[0011] II. Preparation of Etching Solution Precursors:

[0012] Analytical pure iodine (I2) and concentrated nitric acid (HNO3) with a mass percentage concentration ≥65% were added to a corrosion-resistant container at a molar ratio of 1:(8~12). The container was then ultrasonically treated for 5~30 minutes in a closed and ventilated environment under an ultrasonic power of 50~100W to obtain an orange-red solution.

[0013] An oxidation reaction occurs in this step: 10HNO3(conc.) + I2 → 2HIO3 + 10NO2↑ + 4H2O;

[0014] The reaction system gradually changes from colorless to orange-red, indicating the formation of iodic acid (HIO3) and nitrogen dioxide. This step aims to create an acidic environment with HIO3 as the main oxidant, laying the foundation for subsequent oxidation etching of the crystal surface.

[0015] III. Etching Solution Activation and Temperature Control: Add 40%–49% hydrofluoric acid solution (HF) dropwise to the orange-red solution, with the added amount being 10%–20% of the volume of concentrated nitric acid (HNO3), to obtain a colorless solution. The solution quickly fades to colorless, indicating that HF ​​reacts with residual iodides to form volatile hydrogen iodide (HI↑), eliminating color interference and enhancing etching activity. Subsequently, dilute the colorless solution with a mixture of acetic acid (CH3COOH) and deionized water at a volume ratio of 1:(1–2) to obtain a diluted solution. Cool the diluted solution in an ice-water bath to 10±1℃ to obtain the etching solution. Low-temperature etching solutions can suppress side reactions and precisely control the etching rate.

[0016] IV. Single Crystal Etching and Defect Exposure: The crystal with a clean hydrophobic surface obtained in step one is immersed in the etching solution, and ultrasonic etching is performed simultaneously at an ultrasonic frequency of 40 kHz and an ultrasonic power of 50~150 W for 3~10 minutes. After removing the crystal, it is ultrasonically cleaned with anhydrous ethanol for 60 seconds and dried with nitrogen. In this step, the ultrasonic cavitation effect promotes the diffusion of the etchant in the micro-regions of the crystal surface, preferentially attacking defect areas such as dislocation outcrops, forming characteristic morphological pits (such as triangular pyramids and hexagonal pyramids).

[0017] V. Defect Characterization: The presence of etch pits on the crystal surface is observed using a metallographic optical microscope or a scanning electron microscope (SEM). The presence of etch pits indicates dislocation defects, thus revealing the dislocation defects in the lead indium telluride single crystal.

[0018] Furthermore, the abrasive used in the mechanical polishing process described in step one is alumina powder.

[0019] Furthermore, the organic solvent used in the degreasing process described in step one is acetone.

[0020] Furthermore, the dilute acid solution used in step one for deoxidizing is a mixture of dilute hydrochloric acid with a mass percentage concentration of 5% to 7% and dilute nitric acid with a mass percentage concentration of 5% to 7% in a volume ratio of (2.5 to 3.5): 1.

[0021] Furthermore, the inert gas used for inert gas purging in step one is nitrogen.

[0022] Furthermore, the ultrasonic treatment described in step two is performed under conditions of ultrasonic power of 50~100W.

[0023] Furthermore, the ultrasound assistance described in step four is performed under the conditions of an ultrasound frequency of 40 kHz and an ultrasound power of 50~150W.

[0024] PIT crystals (chemical formula PbIn6Te) 10 PIT crystals belong to the trigonal crystal system, with space group R32. This crystal structure directly determines the shape of the etch pits. The trigonal PIT crystal has a triple rotational symmetry axis along the c-axis, i.e., the

[001] direction, and multiple second-order rotational axes perpendicular to the c-axis. On the crystal plane perpendicular to the c-axis (such as the (001) plane), the crystal symmetry exhibits triple rotational symmetry (120° rotational invariance). This means that the atomic arrangement and crystal orientation of the crystal plane on the (001) projection plane have a 120° angle feature.

[0025] The etching process preferentially occurs at crystal defects (such as dislocation outcrops) because the energy in defect regions is higher and they are more easily attacked by chemical etchants. The etch pits are defined by low-index crystal planes (such as the {101} or {110} family of crystal planes), which are controlled by the space group R32 in the trigonal crystal system.

[0026] Due to the trigonal crystal system's 3-fold symmetry, the angle between the {101} or {110} crystal plane families is fixed at 120° (determined by the lattice parameters a = b ≠ c, α = β = 90°, γ = 120°). During etching, the etchant selectively dissolves along these equivalent crystal planes, resulting in triangular pyramidal etch pits with the apex pointing towards

[001] and the pit base being an equilateral triangle. However, for edge dislocations, the strain field is non-axially symmetric, and the etch pits generated on the (001) plane are usually asymmetrical, potentially exhibiting elongated shapes (e.g., isosceles triangles rather than equilateral triangles) or having one side steeper than the others. Sometimes, they may present a semi-hexagonal or irregular quadrilateral shape. For screw dislocations, the strain field is axially symmetric, and on the (001) plane, the outcrop of a pure screw dislocation will produce a highly symmetrical etch pit. For the (001) surface with R32 symmetry, this almost always manifests as a centrally symmetric, regular equilateral triangle or regular hexagonal pit, with the bottom of the pit usually pointed.

[0027] The PIT (Lead Indium Telluride) surface etching method of this invention can form regular and clear triangular pyramidal etch pits on its (001) crystal plane based on the symmetry of the R32 space group of the trigonal crystal system, accurately revealing edge dislocation defects. This method achieves selective etching of defect areas by optimizing the formulation of the HIO3-CH3COOH-HF mixed etching solution system, combined with ultrasonic-assisted processing and precise temperature control, effectively avoiding excessive surface etching. The etch pits obtained by this invention have consistent morphology, sharp edges, and depths between 100 and 300 nm, exhibiting high sensitivity and high reliability. This provides key technical support for evaluating the quality of PIT single crystals, analyzing defect causes, and guiding the optimization of crystal growth processes. Attached Figure Description

[0028] Figure 1 The PbIn6Te treated in step one of Example 1 10 Optical photographs of (PIT) single-crystal surfaces;

[0029] Figure 2 This is a scanning electron microscope image of the PIT single crystal surface after etching in step four of Example 1;

[0030] Figure 3 This is a scanning electron microscope image of the PIT single crystal surface after etching in step four of Example 1. Detailed Implementation

[0031] The beneficial effects of the present invention will be verified using the following examples.

[0032] Example 1: The surface etching method for revealing dislocation defects in lead indium telluride single crystals in this example is performed according to the following steps:

[0033] I. On PbIn6Te 10 (PIT) single crystals undergo pretreatment:

[0034] (1) Using an X-ray crystallography system to determine the PbIn6Te 10 (PIT) The (001) crystal orientation of a single crystal is cut along this crystal plane to obtain a flat wafer with a thickness of 5.0 mm;

[0035] (2) The wafer was mechanically polished in stages using alumina (Al2O3) abrasive water suspension with particle sizes of 15 μm, 5 μm and 1 μm, for 10 minutes at each stage; after each stage of polishing, the wafer was placed in an ultrasonic cleaner with a frequency of 40 kHz and rinsed with deionized water for 1 minute to remove abrasive residue.

[0036] (3) Use alkaline colloidal silica (SiO2) polishing slurry with pH = 10.5 to polish for 60 minutes at a speed of 100 rpm and a pressure of 5 psi to eliminate the subsurface damage layer and obtain a smooth and flat crystal.

[0037] (4) The crystal is immersed in acetone for 10 minutes to degrease, then immersed in a mixture of dilute hydrochloric acid and dilute nitric acid for 10 minutes to remove oxides; then placed in deionized water and cleaned alternately with ultrasonic waves at 40 kHz and 80 kHz for 15 minutes; finally, the surface of the wafer is dried with high-purity nitrogen and dried in a vacuum drying oven at 60°C for 2 hours to obtain a crystal with a clean hydrophobic surface; wherein the mixture of dilute hydrochloric acid and dilute nitric acid is a mixture of 5% dilute hydrochloric acid and 5% dilute nitric acid in a volume ratio of 3:1; before performing the etching process, PbIn6Te 10 (PIT) single crystals undergo systematic pretreatment to ensure surface integrity. This pretreatment step effectively eliminates microcracks caused by mechanical stress and surface-adsorbed impurities, providing a damage-free substrate for subsequent precise exposure of crystal defects. The crystal image after step one is shown below. Figure 1 As shown, from Figure 1 As can be seen, the crystal surface is smooth, bright, and free of scratches.

[0038] II. Preparation of Etching Solution Precursors:

[0039] 2.54 g of analytical grade iodine (I2) and 6.0 mL of 65% concentrated nitric acid (HNO3) were added to a polytetrafluoroethylene container and sonicated for 30 minutes in a closed and ventilated environment at an ultrasonic power of 80W to obtain an orange-red solution.

[0040] An oxidation reaction occurs in this step: 10HNO3(conc.) + I2 → 2HIO3 + 10NO2↑ + 4H2O;

[0041] The reaction system gradually changes from colorless to orange-red, indicating the formation of iodic acid (HIO3) and nitrogen dioxide. This step aims to create an acidic environment with HIO3 as the main oxidant, laying the foundation for subsequent oxidation etching of the crystal surface.

[0042] III. Etching Solution Activation and Temperature Control: 1.0 mL of 40% hydrofluoric acid solution (HF) was added dropwise to the orange-red solution to obtain a colorless solution. The solution quickly faded to colorless, indicating that HF ​​reacted with residual iodide to form volatile hydrogen iodide (HI↑), eliminating color interference and enhancing etching activity. Subsequently, a mixture of 5 mL of acetic acid (CH3COOH) and 10 mL of deionized water was added to the colorless solution for dilution, resulting in a diluted solution. The diluted solution was then cooled to 10±1℃ in an ice-water bath to obtain the etching solution. Low-temperature etching solution can suppress side reactions and precisely control the etching rate.

[0043] IV. Single Crystal Etching and Defect Exposure: The crystal with a clean hydrophobic surface obtained in step one is immersed in the etching solution, and ultrasonic etching is performed simultaneously at a frequency of 40 kHz and a power of 100 W for 5 minutes. After removing the crystal, it is ultrasonically cleaned with anhydrous ethanol for 60 seconds and dried with nitrogen. In this step, the ultrasonic cavitation effect promotes the diffusion of the etchant in the micro-regions of the crystal surface, preferentially attacking defect areas such as dislocation outcrops, forming characteristic morphological pits (such as triangular pyramids and hexagonal pyramids).

[0044] V. Defect Characterization: The crystal surface was observed using a scanning electron microscope (SEM), and the resulting SEM images are shown below. Figure 2 and Figure 3 As shown, from Figure 2 and Figure 3 It can be seen that the pit depth is 100~300 nm, the pit walls are clear and sharp, and the vertices all point to the

[001] crystal orientation. The dislocation type is an edge dislocation. The dislocation defects are accurately revealed without over-etching, thus completing the exposure of dislocation defects in lead indium telluride single crystal.

[0045] The method in this embodiment can accurately reveal dislocation defects in lead indium telluride single crystals, and has the advantages of high sensitivity and high fidelity.

Claims

1. A surface etching method for revealing dislocation defects using indium lead telluride single crystal, characterized in that, This method is performed in the following steps: I. On PbIn6Te 10 Single crystal pretreatment: (1) Use an X-ray crystallography instrument to determine the crystal orientation, cut along the target crystal plane to obtain a wafer; (2) Use micron-sized to submicron-sized abrasives in sequence, and use multi-level gradient mechanical polishing to gradually reduce the surface roughness, while using ultrasonic cleaning to remove abrasive residues; (3) Using alkaline colloidal polishing solution, chemical mechanical polishing is used to eliminate the subsurface damage layer and obtain crystals with smooth and flat surfaces; (4) The crystal surface is then subjected to organic solvent degreasing, dilute acid solution deoxidation, high-purity water multi-frequency ultrasonic rinsing, and finally inert gas purging and low-temperature vacuum drying to obtain a crystal with a clean hydrophobic surface. II. Preparation of Etching Solution Precursors: Analytical pure iodine and concentrated nitric acid with a mass percentage concentration ≥65% were added to a corrosion-resistant container at a molar ratio of 1:(8~12). The container was then ultrasonically treated for 5~30 minutes in a closed and ventilated environment under an ultrasonic power of 50~100W to obtain an orange-red solution. III. Activation and Temperature Control of Etching Solution: Add hydrofluoric acid solution with a mass percentage concentration of 40%~49% dropwise to the orange-red solution, with the amount added being 10%~20% of the volume of concentrated nitric acid, to obtain a colorless solution; then add a mixture of acetic acid and deionized water at a volume ratio of 1:(1~2) to dilute the colorless solution to obtain a diluted solution; then place the diluted solution in an ice-water bath to cool to 10±1℃ to obtain the etching solution; IV. Single Crystal Etching and Defect Exposure: The crystal with a clean hydrophobic surface obtained in step one is immersed in the etching solution, and ultrasound is turned on at a frequency of 40 kHz and an ultrasonic power of 50~150 W for 3~10 minutes to assist etching. After removing the crystal, it is ultrasonically cleaned with anhydrous ethanol for 60 seconds and dried with nitrogen. V. Defect Characterization: The presence of pits on the crystal surface is observed using a metallographic optical microscope or a scanning electron microscope. The presence of pits indicates dislocation defects, thus revealing the dislocation defects in the lead indium telluride single crystal.

2. The surface etching method for revealing dislocation defects in a lead indium telluride single crystal according to claim 1, characterized in that, The abrasive used in the mechanical polishing process described in step one is alumina powder.

3. A surface etching method for revealing dislocation defects in a lead indium telluride single crystal according to claim 1 or 2, characterized in that, The organic solvent used in the degreasing process described in step one is acetone.

4. A surface etching method for revealing dislocation defects in a lead indium telluride single crystal according to claim 1 or 2, characterized in that, The dilute acid solution used in step one for removing oxides is a mixture of dilute hydrochloric acid with a mass percentage concentration of 5% to 7% and dilute nitric acid with a mass percentage concentration of 5% to 7% in a volume ratio of (2.5 to 3.5):

1.

5. A surface etching method for revealing dislocation defects in a lead indium telluride single crystal according to claim 1 or 2, characterized in that, The inert gas used for inert gas purging in step one is nitrogen.

6. A surface etching method for revealing dislocation defects in a lead indium telluride single crystal according to claim 1 or 2, characterized in that, The ultrasonic treatment described in step two is performed under conditions where the ultrasonic power is 50~100W.

7. A surface etching method for revealing dislocation defects in a lead indium telluride single crystal according to claim 1 or 2, characterized in that, The ultrasound assistance described in step four is performed under the conditions of an ultrasound frequency of 40 kHz and an ultrasound power of 50~150 W.

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