A method for measuring the thickness of the p-type layer in a mercury cadmium telluride p-on-n structural material and its application.

Abstract

This invention discloses a method and application for measuring the p-type layer thickness of a mercury cadmium telluride (HCDT) p-on-n structure material. The method measures the carrier concentration and mobility of the HCDT p-on-n structure material at different thicknesses, determines the variation curves of carrier concentration and mobility with thickness, and accurately determines the p-type layer thickness based on the inflection point where the carrier concentration and mobility tend to stabilize on the variation curve. This method is simple to operate, highly accurate, and can provide a reference for the design of downstream device process parameters, supporting the mass production of high-performance p-on-n structure infrared detectors. This method can also provide a reference for adjusting the fabrication process parameters of the HCDT p-on-n structure material, ensuring the optimization of material quality.

Description

Technical Field

[0001] This invention relates to mercury cadmium telluride (HCDT) materials and devices, and in particular to a method and application for measuring the p-type layer thickness of HCDT p-on-n structure materials, which can provide accurate p-type layer thickness values ​​for the fabrication process of high-performance infrared detectors. Background Technology

[0002] Due to its advantages such as high quantum efficiency, low dark current, and the ability to achieve full-infrared detection by adjusting the composition, mercury cadmium telluride (HCdT) has become the most important material for the fabrication of high-performance infrared detectors. Depending on the type of absorption layer, HCdT infrared detectors can be divided into n-on-p and p-on-n types, with p-type and n-type HCdT materials as the absorption layers, respectively. At the same doping concentration, p-type materials have a longer minority carrier lifetime than n-type materials, so theoretically, n-on-p can outperform p-on-n. However, it is difficult to achieve low-concentration doping of p-type materials, and currently, it is difficult to achieve the performance level of p-on-n structures where the absorption layer is more easily doped. HCdT p-on-n has become the main technological route for the mass production of high-performance long-wavelength and very long-wavelength infrared detectors in the future.

[0003] For the fabrication of mercury cadmium telluride (HCdT) p-on-n devices, accurately determining the thickness of the p-type layer is crucial, directly impacting the control over the device fabrication process, especially the electrode via etching. If the measured p-type layer thickness is larger than the actual thickness, designing a larger electrode via depth in the process parameters may result in the p-type layer being etched through, leading to pn junction failure. Conversely, if the measured p-type layer thickness is smaller than the actual thickness, designing a smaller electrode via depth in the process parameters may result in excessively shallow electrode vias, affecting carrier migration and reducing quantum efficiency. Currently, the p-type layer thickness is often determined by measuring the elemental distribution across the cross-section. However, since the elemental doping level is generally very low, this method requires high precision in the testing instruments; insufficient precision can easily lead to large errors. Furthermore, this method cannot obtain the electrical thickness of the p-type layer, thus the measurement itself is inherently inaccurate.

[0004] Currently, the thickness of the p-type layer in mercury cadmium telluride p-on-n structure materials is often determined by measuring the elemental distribution in the cross-section. However, this method is not accurate enough, mainly for two reasons:

[0005] (1) The element doping amount is generally very low. This method requires high precision of the testing instrument. If the precision is insufficient, it is easy to cause large error in the result.

[0006] (2) At the same time, this method cannot obtain the electrical p-type layer thickness, so the test results themselves are inaccurate. Summary of the Invention

[0007] This invention aims to solve the aforementioned technical problems by providing a method for measuring the p-type layer thickness of mercury cadmium telluride (HCdT) p-on-n structure materials. The basic concept of this method includes: based on the precise measurement of thickness, carrier concentration, and mobility during corrosion, the electrical p-type layer thickness can be determined by the inflection point of carrier concentration and mobility changes with thickness. This method is simple to operate, has high measurement accuracy, and can effectively support the research and development and mass production of high-performance long-wavelength, very long-wavelength, and high-operating-temperature HCdT infrared detectors.

[0008] The technical solution of this invention is as follows:

[0009] A method for measuring the thickness of the p-type layer in a mercury cadmium telluride p-on-n structural material includes the following steps:

[0010] (1) Mercury saturated annealing treatment: The prepared p-on-n structure mercury cadmium telluride material was subjected to mercury saturated annealing treatment to eliminate mercury vacancies; at the same time, an n-type auxiliary sheet was selected and subjected to mercury saturated annealing treatment under the same conditions. The auxiliary sheet and the n-type material in the p-on-n structure mercury cadmium telluride material were grown under the same conditions and had similar cutoff wavelengths.

[0011] (2) Thickness Measurement: The original thicknesses of the p-on-n structured mercury cadmium telluride material and the n-type surcharge were measured and denoted as h0 and h, respectively. a ;

[0012] (3) Electrical parameter measurement: After cleaning the material surface and removing the oxide layer, the carrier concentration and mobility of the p-on-n structure mercury cadmium telluride material and the n-type co-sheet were measured and denoted as N0, μ0, and N, respectively. a μ a ;

[0013] (4) Chemical etching: The p-on-n structure mercury cadmium telluride material is etched with a chemical etching solution. Except for the thickness h, the value of h can be adjusted according to the specific precision requirements, preferably in the range of 0.2 to 0.5 μm.

[0014] (5) Measure electrical parameters again: measure the thickness of the remaining material and record it as h1, and test the carrier concentration and mobility of the remaining material again and record them as N1 and μ1, respectively;

[0015] (6) Repeated chemical corrosion and electrical parameter measurement: Steps (4) and (5) were repeated to obtain multiple remaining thicknesses h2, h3, ..., h of the p-on-n structured mercury cadmium telluride material after multiple corrosions. i And multiple carrier concentrations N2, N3, ..., N i Multiple mobility μ2, μ3, ..., μ i , where i≥2, represents the number of corrosion cycles;

[0016] (7) Plot the relationship curve: Plot N i and μ i The curve showing the change of N with the number of corrosion cycles i is used to determine N. i and μ i Both tend to reach a stable inflection point, and the carrier concentration and mobility at this inflection point are the same as those of the n-type co-plate (N). a ) and mobility (μ a Similar to the previous example, the number of erosions at the inflection point is recorded as IP;

[0017] (8) Determine the p-type layer thickness: The thickness of the p-type layer is the difference between the original material thickness and the inflection point thickness, which is h. p =h0-h ip .

[0018] According to the present invention, a method for measuring the p-type layer thickness of a mercury cadmium telluride p-on-n structure material is provided. The mercury cadmium telluride p-on-n structure material can be a bilayer material grown by methods such as liquid phase epitaxy (LPE), molecular beam epitaxy (MBE), and chemical vapor deposition (CVD), or it can be a material formed by p-type ion implantation of an N-type material.

[0019] According to the present invention, a method for measuring the p-type layer thickness of a mercury cadmium telluride p-on-n structural material is provided. The chemical etching solution is an organic or inorganic solution containing elemental bromine. The etching rate is adjusted by controlling the concentration. The etching rate is v, and the value of v can be designed based on the accuracy requirements and the removal thickness h. Preferably, it is between 0.05 μm / min and 0.5 μm / min.

[0020] This invention provides a method for measuring the thickness of the p-type layer in a mercury cadmium telluride (HCdT) p-on-n structure material. This method can accurately measure the thickness of the p-type layer in the HCdT p-on-n structure material, providing a basis for adjusting the preparation process of the p-type layer and enabling precise design of process parameters. At the same time, it can provide a reference for subsequent processes such as mesa etching and electrode hole etching, effectively designing appropriate etching depths.

[0021] The beneficial effects of this invention are:

[0022] This invention determines the changes in carrier concentration and mobility with thickness by measuring the layers-by-layer properties of mercury cadmium telluride (HCdT) p-on-n structure materials. Based on the inflection points on the variation curves, the thickness of the p-type layer is accurately determined. This method is simple to operate, highly accurate, and can provide a reference for the design of downstream device process parameters, supporting the mass production of high-performance p-on-n structure infrared detectors. This method can also provide a reference for adjusting the fabrication process parameters of HCdT p-on-n structure materials, ensuring the optimization of material quality. Attached Figure Description

[0023] Figure 1 The image shows the surface optical morphology of the mercury cadmium telluride p-on-n structure material selected in the embodiments of the present invention.

[0024] Figure 2 The curves showing the variation of carrier concentration and mobility with thickness of the mercury cadmium telluride p-on-n structure material, as well as the determined value of the p-type layer thickness, are plotted for embodiments of the present invention.

[0025] Figure 3 The diagram shows the response signal distribution and blind element distribution of a long-wavelength detector developed based on the p-type layer thickness provided in this embodiment of the invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The embodiments and figures given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0027] The present invention provides the following specific embodiments.

[0028] A method for measuring the thickness of the p-type layer in a mercury cadmium telluride p-on-n structural material includes the following steps:

[0029] (1) Mercury-saturated annealing: p-on-n structured mercury cadmium telluride (MCAD) material and n-type substrates were prepared. The n-type substrate and the n-type material in the p-on-n structured MCAD material were both obtained by horizontal tellurium-rich liquid phase epitaxy, with room temperature cutoff wavelengths of 6.35 μm and 6.37 μm, respectively. The p-type material in the p-on-n structured MCAD material was prepared using in-situ As-doped vertical mercury-rich liquid phase epitaxy. Both the p-on-n structured MCAD material and the n-type substrate were subjected to mercury-saturated annealing under the same conditions to eliminate mercury vacancies.

[0030] (2) Thickness measurement: The original thicknesses of the p-on-n structure mercury cadmium telluride material and the n-type surrogate were measured using an infrared spectrometer, and were h0 = 14.4 μm and ha = 12.5 μm, respectively;

[0031] (3) Electrical parameter measurement: After cleaning the material surface and removing the oxide layer, the carrier concentration and mobility of the p-on-n structure mercury cadmium telluride material and the n-type co-sheet were measured using a Hall effect meter. The values ​​were N0 = 2.28E15 cm⁻¹. -3 (N-type), μ0 = 1.67E4cm 2 / Vs, and Na=3.16E14 cm -3 μa = 9.28E4 cm 2 / Vs;

[0032] (4) Chemical corrosion: The p-on-n structure mercury cadmium telluride material was corroded with a chemical corrosion solution. The corrosion rate was adjusted to about 0.3 μm / min and the corrosion time was 1 min.

[0033] (5) Electrical parameter measurement again: The thickness of the remaining material was measured, and h1 = 14.2 μm was obtained. The carrier concentration and mobility of the remaining material were measured again, and N1 = 2.06E15 cm. -3 (N-type), μ1 = 2.58E4 cm 2 / Vs;

[0034] (6) Repeated chemical corrosion and electrical parameter measurement: Repeat steps (4) and (5) to obtain multiple remaining thicknesses h2, h3, ..., hi of the p-on-n structure mercury cadmium telluride material after multiple corrosions, as well as multiple carrier concentrations N2, N3, ..., Ni, and multiple mobilities μ2, μ3, ..., μi, where i≥2 indicates the number of corrosions;

[0035] (7) Plot the relationship curves: Plot the curves of Ni and μi as a function of corrosion number i. The results are as follows: Figure 2 As shown, the results show that there is an inflection point on the curve where both Ni and μi tend to be stable. At the same time, the carrier concentration and mobility at this inflection point are similar to those of the n-type co-sheet. The number of etchings at the inflection point is recorded as ip = 8. At this number of etchings, the remaining thickness of the p-on-n structure mercury cadmium telluride material is measured to be hip = 12.0 μm.

[0036] (8) Determine the thickness of the p-type layer: The thickness of the p-type layer is the difference between the original material thickness and the inflection point thickness, i.e., hp = h0 - hip = 14.4 - 12.0 = 2.4 μm.

[0037] like Figure 3 The diagram shows the response signal distribution and blind element distribution of a long-wave infrared detector fabricated using the same growth process as the p-on-n structure mercury cadmium telluride material selected in the embodiment. The p-type layer thickness is hp = 2.4, as obtained in the embodiment of this invention. The detector has a size of 640 × 512 (25 μm center-to-center distance), a response signal non-uniformity of 5.4%, and a blind element rate of 0.52%, exhibiting good overall performance.

Claims

1. A method for measuring the thickness of the p-type layer in a mercury cadmium telluride p-on-n structural material, characterized in that, Includes the following steps: (1) Prepare p-on-n structure mercury cadmium telluride material and n-type surface, and perform mercury saturation annealing treatment on the p-on-n structure mercury cadmium telluride material and n-type surface under the same conditions to eliminate mercury vacancies. The surface and the n-type material in the p-on-n structure mercury cadmium telluride material are grown under the same conditions and have similar cutoff wavelengths. (2) Measure the original thickness of the p-on-n structure mercury cadmium telluride material and the n-type surrogate sheet, and record them as h0 and h0, respectively. a ; (3) Clean the surface of the material and remove the oxide layer. Measure the carrier concentration and mobility of the p-on-n structure mercury cadmium telluride material and the n-type co-sheet, and record them as N0, μ0, and N, respectively. a μ a ; (4) The p-on-n structure mercury cadmium telluride material was etched with a chemical etching solution to remove a thickness of h; (5) Measure the thickness of the remaining material and record it as h1. Then test the carrier concentration and mobility of the remaining material again and record them as N1 and μ1, respectively. (6) Repeat steps (4) and (5) to obtain multiple remaining thicknesses h2, h3, ..., h of the p-on-n structured mercury cadmium telluride material after multiple corrosions. i And multiple carrier concentrations N2, N3, ..., N i and multiple mobility μ2, μ3, ..., μ i , where i represents the number of corrosions, i≥2; (7) Draw N i and μ i The curve showing the change of N with the number of corrosion cycles i is used to determine N. i and μ i Both tend towards a stable inflection point, and the carrier concentration and mobility at this inflection point are the same as the carrier concentration N of the n-type co-plate. a and mobility μ a Similar, the number of erosions at the inflection point is recorded as IP; (8) Determine the thickness of the p-type layer, wherein the thickness h of the p-type layer is... p The original material thickness h0 and the inflection point thickness h ip The difference h p =h0-h ip .

2. The method for measuring the thickness of the p-type layer of a mercury cadmium telluride p-on-n structural material as described in claim 1, characterized in that: The value of h is designed according to specific accuracy requirements.

3. The method for measuring the thickness of the p-type layer of a mercury cadmium telluride p-on-n structural material as described in claim 2, characterized in that: The value of h is 0.2~0.5μm.

4. The method for measuring the thickness of the p-type layer of a mercury cadmium telluride p-on-n structural material as described in claim 1, characterized in that: The aforementioned mercury cadmium telluride p-on-n structure material is a bilayer material grown by liquid phase epitaxy (LPE), molecular beam epitaxy (MBE), or chemical vapor deposition (CVD), or a material formed by p-type ion implantation into an N-type material.

5. The method for measuring the thickness of the p-type layer of a mercury cadmium telluride p-on-n structural material as described in claim 1, characterized in that: The chemical etching solution is an organic or inorganic solution containing elemental bromine.

6. The method for measuring the thickness of the p-type layer of a mercury cadmium telluride p-on-n structural material as described in claim 5, characterized in that: The corrosion rate v can be adjusted by controlling the concentration of the chemical etching solution.

7. The method for measuring the thickness of the p-type layer of a mercury cadmium telluride p-on-n structural material as described in claim 6, characterized in that: The corrosion rate v is designed based on a comprehensive consideration of accuracy requirements and removal thickness design.

8. The method for measuring the thickness of the p-type layer of a mercury cadmium telluride p-on-n structural material as described in claim 7, characterized in that: The corrosion rate v is 0.05 μm / min to 0.5 μm / min.

9. The application of the method for measuring the p-type layer thickness of a mercury cadmium telluride p-on-n structural material as described in any one of claims 1-8, characterized in that: The thickness of the p-type layer of the mercury cadmium telluride p-on-n structure material measured by the method is used as the basis for adjusting the preparation process of the p-type layer, so as to achieve precise design of process parameters.

10. The application of the method for measuring the p-type layer thickness of a mercury cadmium telluride p-on-n structural material as described in any one of claims 1-8, characterized in that: The p-type layer thickness of the mercury cadmium telluride p-on-n structure material, measured by the method described above, is used to design the etching depth for subsequent mesa etching and electrode hole etching.

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