Method for measuring minority carrier diffusion length of tellurium-cadmium-mercury film

Abstract

The invention relates to a method for measuring the minority carrier diffusion length of a mercury cadmium telluride film. The method comprises the following steps: designing pixel arrays with different numbers and different shapes; preparing a pixel array on the tellurium-cadmium-mercury film material and leading the pixel array to a test pin; under uniform incident light, the total light current of all the arrays is measured by using the test pins; calculating the area of a total carrier collection region after the pixel array is expanded; establishing a total photocurrent calculation model based on the extended carrier collection region; and fitting the calculation model according to the array parameters and the light current test result to obtain the minority carrier diffusion length. The minority carrier diffusion length measurement method provided by the invention can be applied to a mercury-cadmium-telluride infrared chip which is subjected to a multi-step material chip process and has a complex pixel structure, and a simple, rapid and high-universality method is provided for material characterization of a mercury-cadmium-telluride infrared film.

Description

Technical Field

[0001] The invention belongs to the field of infrared and optoelectronics, and specifically relates to a method for measuring the minority carrier diffusion length of a mercury cadmium telluride film. Background Art

[0002] Mercury cadmium telluride thin film materials have long been used in the preparation of infrared photodetectors due to their advantages such as adjustable band gap, high mobility, and long carrier lifetime. Material parameters such as minority carrier diffusion length and minority carrier lifetime determine the photoelectric performance of the detector. The measurement of the minority carrier diffusion length of mercury cadmium telluride thin films plays an important role in testing the quality of material growth and improving device structure design.

[0003] The minority carrier diffusion length of infrared detectors is generally measured by the laser beam induced current (LBIC) method. LBIC focuses the laser into a micrometer or even nanometer-level spot, forms localized light excitation on the surface of the material, and then relies on the PN junction electric field in the material to collect photogenerated carriers, and fits the diffusion length of the material based on the photocurrent decay. Since the PN junction is a minority carrier device, the working principle mainly depends on the injection and recombination of minority carriers, so the parameter obtained by photocurrent fitting is the minority carrier diffusion length. The LBIC method can only measure the minority carrier diffusion length near the surface of the planar junction material. Since mercury cadmium telluride infrared photodetectors generally use a back-incident structure, and the surface needs to undergo processes such as etching micro-tables and multi-layer passivation, the application of the LBIC method is severely limited.

[0004] Therefore, there is currently a lack of a universal method for measuring the minority carrier diffusion length of infrared thin film materials. Summary of the invention

[0005] The purpose of the present invention is to provide a method for measuring the minority carrier diffusion length of a mercury cadmium telluride thin film, so as to solve the difficulty that the traditional method has poor applicability to infrared optoelectronic devices that undergo multiple process steps. The minority carrier diffusion length of the mercury cadmium telluride thin film material can be measured simply and quickly based on the conventional blackbody response test method of the infrared optoelectronic device.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A method for measuring the minority carrier diffusion length of a mercury cadmium telluride film, the method specifically comprising the following steps:

[0008] S1, fabrication of infrared optoelectronic devices for measuring minority carrier diffusion length of HgCdTe thin films;

[0009] S2, measure the photocurrent of different arrays. Based on the blackbody response test of infrared detector, provide uniform incident light to the HgCdTe film, and use the test pin to measure the total photocurrent I of each pixel array. light ;

[0010] S3, calculating the area of ​​the carrier collection region after the pixel array is expanded, and establishing a total photocurrent model after the expansion;

[0011] S4, according to the total photocurrent model of step S3, fitting and obtaining the minority carrier diffusion length.

[0012] The specific implementation method of step S1 includes the following sub-steps:

[0013] S11, designing a pixel array; setting the pixel center distance based on the estimated minority carrier diffusion length, designing pixel arrays with different numbers of pixels and array shapes, and the pixel arrays have different perimeter / area ratios;

[0014] S12, preparing a pixel array; preparing the pixel array of step S11 on the mercury cadmium telluride film and leading it to the test pin.

[0015] The specific implementation method of step S12 includes the following sub-steps:

[0016] S121, forming an N-type doped region array on the P-type mercury cadmium telluride film by an ion implantation process, wherein the N-type region is arranged according to the pixel array designed in step S12;

[0017] S122, the pixel array is led out to the test pin. The N-type region of the PN junction is connected to the external test pin by using the reverse solder interconnection process; wherein all the PN junctions in the same array are connected to the same test pin to form an electrical parallel connection.

[0018] The specific implementation method of step S3 includes the following sub-steps:

[0019] S31, calculate the carrier collection area S inside the pixel array in , the carrier collection area inside the pixel array can be expressed as:

[0020]

[0021] Where n is the pixel array specification, d pitch is the pixel center distance;

[0022] S32, calculate the carrier collection area S extended by the edge of the pixel array exp , assuming that the minority carrier diffusion length is x, the carrier collection area extended at the edge of the pixel array can be expressed as:

[0023] S exp =x·L (2)

[0024] Where L is the perimeter of the pixel array;

[0025] S33, calculate the total carrier collection area S after array expansion all, the total carrier collection area after expansion can be expressed as:

[0026] S all =S in +S exp (3)

[0027] S34, the extended total photocurrent model, taking the photocurrent density of HgCdTe film as I d , then the total photocurrent calculation formula can be expressed as:

[0028]

[0029] According to the number of pixels, perimeter, center distance and total photocurrent test results of the array, the unknown parameter I of the total photocurrent calculation formula is calculated by fitting. d and x, and x is the minority carrier diffusion length of the corresponding HgCdTe film.

[0030] The advantages of the present invention are: a high-density pixel array is prepared on a mercury cadmium telluride film, allowing photogenerated carriers to diffuse laterally between pixels to form crosstalk current. By designing pixel arrays with different perimeter / area ratios, measuring and analyzing the ratio of external crosstalk current to photocurrent in the array, the extended range of the pixel array collecting photogenerated carriers is calculated. Since the photogenerated carrier collection area extended at the edge of the pixel array depends on the minority carrier diffusion process of the device, the minority carrier diffusion length of the mercury cadmium telluride film can be simply and quickly calculated. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of pixel arrays of different specifications according to the first embodiment of the present invention;

[0032] Figure 2 is a schematic diagram of pixel arrays of the same specification and different shapes according to the second embodiment of the present invention;

[0033] Figure 3 It is a schematic diagram of the structure of an infrared photoelectric device used to measure the minority carrier diffusion length of mercury cadmium telluride thin film;

[0034] In the figure: 1- mercury cadmium telluride film, 2- picture element, 3- indium column, 4- metal lead, 5- substrate. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with the accompanying drawings, which are only used for exemplary description and cannot be understood as limiting the present invention.

[0036] In order to more concisely describe the present embodiment, some parts known to those skilled in the art but not related to the main content of the present invention are omitted in the drawings or descriptions. In addition, for the convenience of description, some parts in the drawings are omitted, enlarged or reduced, but they do not represent the size or entire structure of the actual product.

[0037] The present invention discloses a method for measuring the minority carrier diffusion length of a mercury cadmium telluride film, the method specifically comprising the following steps:

[0038] S1, manufacturing an infrared photoelectric device for measuring the minority carrier diffusion length of the mercury cadmium telluride film 1;

[0039] The specific implementation method of step S1 includes the following sub-steps:

[0040] S11, design the pixel array; set the pixel center distance based on the estimated minority carrier diffusion length, and the pixel center distance should be close to the estimated minority carrier diffusion length; make the external crosstalk current of the pixel array and the photocurrent in the array have similar magnitudes to facilitate subsequent fitting calculations.

[0041] Pixel arrays with different numbers of pixels and array shapes are designed, and the pixel arrays have different perimeter / area ratios, so as to ensure that each pixel array has a different ratio of external crosstalk current and photocurrent within the array.

[0042] S12, preparing a pixel array; preparing the pixel array of step S11 on the mercury cadmium telluride film 1 and leading it to the test pin.

[0043] The specific implementation method of step S12 includes the following sub-steps:

[0044] S121, forming an N-type doped region array on the P-type mercury cadmium telluride film 1 by an ion implantation process, wherein the N-type region is arranged according to the pixel array designed in step S12;

[0045] S122, the pixel array is led out to the test pin. The N-type region of the PN junction is connected to the external test pin by using the reverse solder interconnection process; wherein all the PN junctions in the same array are connected to the same test pin to form an electrical parallel connection.

[0046] like Figure 3 As shown, the infrared optoelectronic device for measuring the minority carrier diffusion length of the mercury cadmium telluride film 1 manufactured by the above steps includes the mercury cadmium telluride film 1 and the pixel array thereon, the indium column 3, the metal lead 4 and the substrate 5, and the metal lead 4 is connected to the external test pin.

[0047] S2, measure the photocurrent of different arrays. Based on the blackbody response test of infrared detector, provide uniform incident light to the mercury cadmium telluride film 1, and use the test pin to measure the total photocurrent I of each pixel array light ;

[0048] S3, calculating the area of ​​the carrier collection region after the pixel array is expanded, and establishing a total photocurrent model after the expansion;

[0049] The specific implementation method of step S3 includes the following sub-steps:

[0050] S31, calculate the carrier collection area S inside the pixel array in , the carrier collection area inside the pixel array can be expressed as:

[0051]

[0052] Where n is the pixel array specification, d pitch is the pixel center distance;

[0053] S32, calculate the carrier collection area S extended by the edge of the pixel array exp , assuming that the minority carrier diffusion length is x, the carrier collection area extended at the edge of the pixel array can be expressed as:

[0054] S exp =x·L (2)

[0055] Where L is the perimeter of the pixel array;

[0056] S33, calculate the total carrier collection area S after array expansion all , the total carrier collection area after expansion can be expressed as:

[0057] S all =S in +S exp (3)

[0058] S34, the expanded total photocurrent model, taking the photocurrent density of HgCdTe film 1 as I d , then the total photocurrent calculation formula can be expressed as:

[0059]

[0060] S4, according to the total photocurrent model of step S3, the minority carrier diffusion length is obtained by fitting. According to the number of pixels, perimeter, center distance and total photocurrent test results of the array, the unknown parameter I of the total photocurrent calculation formula is calculated by fitting. d and x, and x is the minority carrier diffusion length of the corresponding HgCdTe film.

[0061] Embodiment 1, as Figure 1 As shown, an infrared photoelectric device for measuring the minority carrier diffusion length of a mercury cadmium telluride film is prepared. Ions are implanted in a specific area of ​​the mercury cadmium telluride film 1 to form pixel arrays of different specifications consisting of different numbers of pixels 2. The pixel arrays are designed with different specifications corresponding to different perimeters.

[0062] Table 1 Parameters of pixel arrays of different specifications

[0063]

[0064] The infrared photoelectric device is used for black body response test, and the total photocurrent I of each array is measured. light The results are shown in Table 1. According to the parameters listed in Table 1, the photocurrent density I d =10 -12 A / μm 2 And the minority carrier diffusion length x = 5μm.

[0065] Embodiment 2, as Figure 2 As shown, an infrared optoelectronic device for measuring the minority carrier diffusion length of a mercury cadmium telluride film is prepared. Ions are implanted in a specific area of ​​the mercury cadmium telluride film 1 to form a pixel array of the same specification and different shapes composed of the same number of pixels 2. The pixel array is designed with the same specification, but the array shape is different, corresponding to different perimeters.

[0066] Table 2 Parameters of pixel arrays with the same specifications and different shapes

[0067]

[0068] The infrared photoelectric device is used for black body response test, and the total photocurrent I of each array is measured. light The results are shown in Table 2. According to the parameters listed in Table 2, the photocurrent density I d =2×10 -12 A / μm 2 And the minority carrier diffusion length x = 8μm.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. That is, any equivalent changes and modifications made according to the content of the patent application scope of the present invention should be within the technical scope of the present invention.

Claims

1. A method for measuring the minority carrier diffusion length of a mercury cadmium telluride thin film, characterized in that: The method specifically comprises the following steps: S1, manufacturing an infrared photoelectric device for measuring the minority carrier diffusion length of a mercury cadmium telluride thin film (1); S2, measuring the photocurrent of different arrays; based on the black body response test of the infrared detector, providing uniform incident light to the mercury cadmium telluride film (1), and using the test pin to measure the total photocurrent I of each pixel array light ; S3, calculating the area of ​​the carrier collection region after the pixel array is expanded, and establishing a total photocurrent model after the expansion; S4, according to the total photocurrent model of step S3, fitting and obtaining the minority carrier diffusion length.

2. The method for measuring the minority carrier diffusion length of a mercury cadmium telluride thin film according to claim 1, characterized in that: The specific implementation method of step S1 includes the following sub-steps: S11, designing pixel arrays; setting pixel center distances based on the estimated minority carrier diffusion length; designing pixel arrays with different numbers of pixels and array shapes, and pixel arrays with different perimeter / area ratios; S12, preparing a pixel array; The pixel array of step S11 is prepared on the mercury cadmium telluride film (1) and is led out to the test pin.

3. The method for measuring the minority carrier diffusion length of a mercury cadmium telluride thin film according to claim 2, characterized in that: The specific implementation method of step S12 includes the following sub-steps: S121, forming an N-type doped region array on the P-type mercury cadmium telluride film (1) by using an ion implantation process, wherein the N-type region is arranged according to the pixel array designed in step S12; S122, the pixel array is led out to the test pin. The N-type region of the PN junction is connected to the external test pin by using the reverse solder interconnection process; wherein all the PN junctions in the same array are connected to the same test pin to form an electrical parallel connection.

4. The method for measuring the minority carrier diffusion length of a mercury cadmium telluride thin film according to claim 1, characterized in that: The specific implementation method of step S3 includes the following sub-steps: S31, calculate the carrier collection area S inside the pixel array in , the carrier collection area inside the pixel array can be expressed as: Where n is the pixel array specification, d pitch is the pixel center distance; S32, calculate the carrier collection area S extended by the edge of the pixel array exp , assuming that the minority carrier diffusion length is x, the carrier collection area extended at the edge of the pixel array can be expressed as: S exp =x·L (2) Where L is the perimeter of the pixel array; S33, calculate the total carrier collection area S after array expansion all , the total carrier collection area after expansion can be expressed as: S all =S in +S exp (3) S34, the extended total photocurrent model, taking the photocurrent density of the HgCdTe film (1) as I d , then the total photocurrent calculation formula can be expressed as:

5. The method for measuring the minority carrier diffusion length of a mercury cadmium telluride thin film according to claim 4, characterized in that: According to the number of pixels, perimeter, center distance and total photocurrent test results of the array, the unknown parameter I of the total photocurrent calculation formula is calculated by fitting. d and x, and x is obtained as the minority carrier diffusion length of the corresponding HgCdTe film (1).

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