A method for measuring light extraction efficiency and internal quantum efficiency of LED chips

Abstract

The present invention discloses a method for measuring the light extraction efficiency and internal quantum efficiency of an LED chip. The method comprises the following steps: measuring at least three different x n The external quantum efficiency E of the LED chip n , where x n Indicates the ratio of the area of ​​the smooth surface of the LED chip's light-emitting surface to the area of ​​the total light-emitting surface, 0<x n <1; according to E n with x n The value of the formula [x n a+(1‑x n )b]c=E n Perform nonlinear fitting to obtain constants a, b, and c, and then calculate the light extraction efficiency of the LED LEE = x n a+(1‑x n )b and internal quantum efficiency (IQE) = c. Because actual LED chips incorporate reflectors, roughened surfaces, and other structures that enhance light extraction efficiency, the light extraction pattern is complex. The LED light extraction efficiency obtained through simulation and PL measurement differs significantly from the actual light extraction efficiency of the LED chip. This measurement method, based on actual measurement results, better reflects the actual light extraction efficiency and internal quantum efficiency of the LED chip.

Description

Technical Field

[0001] The present invention relates to the field of light emitting diode measurement, and in particular to a method for measuring the light extraction efficiency and internal quantum efficiency of an LED chip. Background Art

[0002] Since its inception, display technology has undergone a century of technological innovation and has penetrated into every corner of life. Among the many current display technologies, Micro-LED display technology is considered to be a disruptive next-generation display technology and has received widespread attention from many related companies and research institutions. Micro-LED display technology is a self-luminous display technology that integrates arrayed micron-level LED light-emitting devices (Micro-LEDs) on an active addressing drive substrate to achieve individual control of each pixel to output the display image. Micro-LED displays have many advantages such as self-luminescence, high efficiency, low power consumption, high integration, and high stability. They are also small in size, highly flexible, and easy to disassemble and merge. They can be applied to any existing display application from small to large sizes.

[0003] However, Micro LED technology currently faces numerous challenges, one of which is the Micro LED size effect. When chip size is reduced to the micron level, efficiency drops sharply. As the chip size decreases, the proportion of the chip sidewall gradually increases. Dangling bonds, defects, and impurities on the surface lead to increased surface recombination, resulting in a decrease in internal quantum efficiency. At the same time, as the chip size decreases, the thin-film chip changes from a single-sided light output of conventional size to a five-sided light output. The surface state of the top surface and the sidewalls is different, resulting in inconsistent light extraction efficiency between the sidewalls and the top surface. Therefore, the external quantum efficiency of Micro LED is affected by both reduced internal quantum efficiency and reduced light extraction efficiency.

[0004] Currently, there are few methods that can effectively determine the internal quantum efficiency and light extraction efficiency of LEDs. The internal quantum efficiency of LEDs is generally estimated using variable-temperature EL or variable-temperature PL methods, while the light extraction efficiency is evaluated using optical tracing. However, the variable-temperature PL method is not only cumbersome but can only measure the internal quantum efficiency of LED epitaxial wafers, not the LED chip itself. Optical tracing, on the other hand, requires numerous parameters and is difficult to calibrate with experimental data. While the variable-temperature EL method can measure the internal quantum efficiency of LED chips, it requires very low temperatures, resulting in a lengthy measurement process and the risk of measurement failure due to insufficient cooling, poor chip contact, or chip burnout at low temperatures.

[0005] In order to more clearly understand how the efficiency of Micro LED chips changes with size, it is urgent to propose a method to measure the light extraction efficiency and internal quantum efficiency of LED chips. Summary of the Invention

[0006] The object of the present invention is to provide a method for measuring the light extraction efficiency and internal quantum efficiency of an LED chip.

[0007] The object of the present invention is achieved like this:

[0008] A method for measuring the light extraction efficiency and internal quantum efficiency of an LED chip, characterized by measuring at least three different x n The external quantum efficiency E of the LED chip n , where x n Indicates the ratio of the area of ​​the smooth surface of the LED chip's light-emitting surface to the area of ​​the total light-emitting surface, 0<x n <1; according to E n with x n The value of the LED is obtained by nonlinear fitting through formula (1) to obtain the constants a, b, and c, thereby calculating the light extraction efficiency of the LED LEE = x n a+(1-x n )b and internal quantum efficiency IQE=c, formula (1) is as follows:

[0009] [x n a+(1-x n )v]c=E n (1).

[0010] Furthermore, the LED chip includes a conductive substrate, a metal bonding layer, a first electrode, a semiconductor layer, a passivation layer, and a second electrode from bottom to top; the total light-emitting surface includes the side walls of the semiconductor layer and the area of ​​the upper surface of the semiconductor layer not covered by the second electrode.

[0011] Furthermore, the total light-emitting surface of the LED chip includes a smooth surface and a roughened surface, the sidewall of the semiconductor layer is a smooth surface; the upper surface of the semiconductor layer is entirely a roughened surface, or part of the smooth surface and part of the roughened surface.

[0012] Further, the following steps are included:

[0013] S1. Prepare n groups of LED chips required for measurement;

[0014] S2. Measure the ratio of the smooth surface area of ​​each LED chip to the total light-emitting surface area x n ;

[0015] S3. Measure the external quantum efficiency E of each group of LED chips at the same current density. n ;

[0016] S4, Lianli E n with x n Get E n -xn Relationship curve;

[0017] S5. Using formula (1), the curve E n -x n Nonlinear fitting is performed and stable parameters a, b, and c are obtained through multiple iterations; a is a constant representing the light extraction efficiency of the smooth surface, b is a constant representing the light extraction efficiency of the rough surface, and c is a constant representing the internal quantum efficiency of the LED chip; <a<1,0<b<1,0<c<1。

[0018] Furthermore, in step S1, n groups of LED chips are prepared, where n≥3, and the areas of the smooth surfaces of the n groups of LED chips are S 11 、S 21 、S 31 …S n1 , the roughened surface areas of n groups of LED chips are S 12 、S 22 、S 32 …S n2 , where S 11 ≠S 21 ≠S 31 …≠S n1 , S 12 ≠S 22 ≠S 32 …≠S n2 .

[0019] Furthermore, the ratio of the area of ​​the smooth surface to the area of ​​the total light-emitting surface in step S2 is x n By formula Calculated, where S n1 is the area of ​​the smooth surface of the nth group of chips, S n2 is the area of ​​the roughened surface; the area of ​​the smooth surface of n groups of LED chips accounts for x1, x2, x3...x respectively in the total light-emitting surface area. n The ratio of the roughened surface area of ​​n groups of LED chips to the total light emitting surface area is 1-x1, 1-x2, 1-x3...1-x n .

[0020] Furthermore, in step S3, the external quantum efficiency E of the LED chip at the same current density is n The measurement method is to apply a current I between the first electrode and the second electrode of the LED chip, and use a semiconductor analyzer to measure the light power P and the emission wavelength λ of the LED chip; according to the formula Calculate the external quantum efficiency E of the LED n , the actual external quantum efficiencies of n groups of chips are E1, E2, E3, ...E n .

[0021] Since actual LED chips integrate structures such as reflectors and roughened surfaces to improve light extraction efficiency, the light extraction pattern is relatively complex. The LED light extraction efficiency obtained by simulation and PL measurement is significantly different from the actual light extraction efficiency of the LED chip. The measurement method of the present invention is based on actual measurement results and can better reflect the actual light extraction efficiency and internal quantum efficiency of the LED chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart of a method for measuring the light extraction efficiency and internal quantum efficiency of an LED chip according to the present invention;

[0023] Figure 2 This is a cross-sectional view of the structure of an LED chip with smooth sidewalls and a rough top in Example 1 of the present invention;

[0024] Figure 3 1 is a top view of a measurement pattern of an LED chip with smooth sidewalls and a rough top in Example 1 of the present invention;

[0025] Figure 4 is the external quantum efficiency E of the LED chip with smooth sidewalls and rough table top in Example 1 of the present invention. n The ratio of the LED chip smooth surface area to the total light emitting surface area (E n -x n ) relationship curve and fitting curve diagram;

[0026] Figure 5 is a cross-sectional view of the structure of the LED chip in Example 2 of the present invention;

[0027] Figure 6 is the external quantum efficiency E of the LED chip in Example 2 of the present invention n As the ratio of the LED smooth surface area to the total light emitting surface area (E n -x n ) relationship curve and fitting curve diagram. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. In addition, the drawings of the present invention are all simplified and non-precisely scaled, and are only used for the convenience and clarity of the auxiliary description of the present invention.

[0029] Example 1: Measuring the Light Extraction Efficiency and Internal Quantum Efficiency of an InGaN Red LED Chip with a Silicon Substrate and Smooth Sidewalls and Rough Mesas

[0030] 1. Prepare LED chips for measuring light extraction efficiency and internal quantum efficiency of LED chips. The LED chip structure is as follows: Figure 2As shown, the LED chip includes, from bottom to top, a conductive substrate, a metal bonding layer, a first electrode, a first semiconductor layer, an active layer, a second semiconductor layer, and a second electrode; the sidewalls of the first semiconductor layer, the sidewalls of the active layer, the sidewalls of the second semiconductor layer, and the area of ​​the upper surface of the second semiconductor layer not covered by the second electrode are all light-emitting surfaces, and the light-emitting surfaces include a smooth surface and a roughened surface; as shown Figure 2 As shown, the chip sidewalls are smooth and the upper surface is rough;

[0031] 2. Prepare 4 groups of Figure 2 The LED chips shown are red light LED chips with radial sizes of 100 μm, 50 μm, 20 μm, and 10 μm, respectively. The top surface of the LED chip is a roughened surface, and the side wall is a smooth surface.

[0032] The smooth surface area of ​​a 100μm LED chip is 0.0012mm 2 , the roughened surface area is 0.01mm 2 The smooth surface area of ​​a 50μm LED chip is 0.0006mm 2 , the roughened surface area is 0.0025mm 2 The smooth surface area of ​​a 20μm LED chip is 0.00024mm 2 , the roughened surface area is 0.0004mm 2 The smooth surface area of ​​a 10μm LED chip is 0.00012mm 2 , the roughened surface area is 0.0001mm 2 ;

[0033] 3. According to the formula Calculate the ratio of the smooth surface area of ​​the LED chip to the total light emitting surface area x n , then the ratio of the area of ​​the roughened surface to the total area of ​​the light-emitting surface is 1-x n The ratios of the smooth surface area to the total light-emitting surface area of ​​the four groups of LED chips are 0.107, 0.193, 0.375, and 0.545, respectively; the ratios of the roughened surface area to the total light-emitting surface area of ​​the four groups of LED chips are 0.893, 0.807, 0.625, and 0.455, respectively;

[0034] 4. Measure the external quantum efficiency of LED chips:

[0035] Apply current I between the first electrode and the second electrode of the LED chip, and use a semiconductor analyzer to measure the light power P and the emission wavelength λ of the LED chip; according to the formula Calculate the external quantum efficiency E of the LED chip n ;

[0036] The external quantum efficiency of red LED chips with radial sizes of 100μm, 50μm, 20μm, and 10μm at a current density of 1A / cm 2 They are 13.8%, 12.9*, 11.7%, and 9.8% respectively;

[0037] 5. Measure the light extraction efficiency and internal quantum efficiency of LED chips:

[0038] Calculate the external quantum efficiency E of n groups of LED chips n The ratio of the smooth surface area of ​​the LED chip to the total light emitting surface area x n Combined, we get the external quantum efficiency E of the LED chip n The ratio of the smooth surface area of ​​the LED chip to the total light emitting surface area x n The relationship curve E n -x n ,like Figure 4 As shown;

[0039] 6. Using the formula [x n a+(1-x n )b]c=E n For curve E n -x n Nonlinear fitting was performed and multiple iterations were performed to obtain the extraction efficiency of the smooth surface a = 20.6%, the extraction efficiency of the rough surface b = 51.4%, and the internal quantum efficiency of the LED chip c = 28.6%.

[0040] 7. According to the formula LEE = x n a+(1-x n )b Further calculation shows that the extraction efficiencies of Micro LED chips with sizes of 100*100μm, 50*50μm, 20*20μm, and 10*10μm are 48.1%, 45.5%, 39.9%, and 34.6%, respectively.

[0041] Example 2: Measuring the light extraction efficiency and internal quantum efficiency of an InGaN yellow LED chip with smooth sidewalls, a smooth outer portion of the upper surface, and a rough middle portion

[0042] 1. Prepare 4 groups of Figure 5 The radial dimensions of the three LED chips are all 1000 μm, and the smooth surface area of ​​the first LED chip is 0.16 mm. 2 , the area of ​​the roughened surface is 0.84mm 2 The smooth surface area of ​​the second group of LED chips is 0.25mm 2 , the roughened surface area is 0.75mm 2 The smooth surface area of ​​the first group of LED chips is 0.49mm2 , the area of ​​the roughened surface is 0.51mm 2 ;

[0043] 2. According to the formula Calculate the ratio of the smooth surface area of ​​the LED chip to the total light emitting surface area x n , then the ratio of the area of ​​the roughened surface to the total area of ​​the light-emitting surface is 1-x n The ratios of the smooth surface area of ​​the four LED chips to the total light-emitting surface area are 0.1, 0.16, 0.26, and 0.49, respectively; the ratios of the roughened surface area of ​​the four LED chips to the total light-emitting surface area are 0.99, 0.84, 0.75, and 0.51, respectively.

[0044] 3. Measure the external quantum efficiency of LED chips:

[0045] Apply current I between the first electrode and the second electrode of the LED chip, and use a semiconductor analyzer to measure the light power P and the emission wavelength λ of the LED chip; according to the formula Calculate the external quantum efficiency EQE of LED chips, 4 groups of chips at a current density of 1A / cm 2 23.3%, 20.8%, 19.6*, 16.2% respectively;

[0046] 4. Measure the light extraction efficiency and internal quantum efficiency of LED chips:

[0047] Calculate the external quantum efficiency E of n groups of LED chips n The ratio of the smooth surface area of ​​the LED chip to the total light emitting surface area x n Combined, we get the external quantum efficiency E of the LED chip n The ratio of the smooth surface area of ​​the LED chip to the total light emitting surface area x n The relationship curve E n -x n ,like Figure 6 As shown;

[0048] 5. Using the formula [x n a+(1-x n )b]c=E n For curve E n -x n Nonlinear fitting was performed and multiple iterations were performed to obtain the extraction efficiency a of the smooth surface = 15.4%, the extraction efficiency b of the roughened surface = 52.3%, and the internal quantum efficiency c of the LED chip = 46.1%.

[0049] The above embodiments merely express the technical implementation methods of the present invention. The descriptions thereof are relatively specific and detailed, but they should not be construed as limiting the patents of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified or some of the technical features thereof may be replaced by equivalents; and such modifications or replacements do not deviate from the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring the light extraction efficiency and internal quantum efficiency of an LED chip, characterized by: Measure at least three different x n The external quantum efficiency E of the LED chip n , where x n Indicates the ratio of the area of ​​the smooth surface of the LED chip's light-emitting surface to the area of ​​the total light-emitting surface, 0<x n <1; according to E n with x n The value of the LED is obtained by nonlinear fitting through formula (1) to obtain the constants a, b, and c, thereby calculating the light extraction efficiency of the LED LEE = x n a+(1-x n )b and internal quantum efficiency IQE=c, formula (1) is as follows: [x n a+(1-x n )b]c=E n (1)。 2. The method for measuring light extraction efficiency and internal quantum efficiency of an LED chip according to claim 1, wherein: The LED chip includes, from bottom to top, a conductive substrate, a metal bonding layer, a first electrode, a semiconductor layer, a passivation layer, and a second electrode; the total light-emitting surface includes the side walls of the semiconductor layer and the area on the upper surface of the semiconductor layer not covered by the second electrode.

3. The method for measuring light extraction efficiency and internal quantum efficiency of an LED chip according to claim 2, wherein: The total light-emitting surface of the LED chip includes a smooth surface and a rough surface. The side wall of the semiconductor layer is a smooth surface. The upper surface of the semiconductor layer is entirely a rough surface, or part of the smooth surface and part of the rough surface.

4. The method for measuring light extraction efficiency and internal quantum efficiency of an LED chip according to claim 1, wherein: The following steps are involved: S1. Prepare n groups of LED chips required for measurement; S2. Measure the ratio of the smooth surface area of ​​each LED chip to the total light-emitting surface area x n ; S3. Measure the external quantum efficiency E of each group of LED chips at the same current density. n ; S4, Lianli E n with x n Get E n -x n Relationship curve; S5. Using formula (1), the curve E n -x n Nonlinear fitting is performed and stable parameters a, b, and c are obtained through multiple iterations; a is a constant representing the light extraction efficiency of the smooth surface, b is a constant representing the light extraction efficiency of the rough surface, and c is a constant representing the internal quantum efficiency of the LED chip; <a<1,0<b<1,0<c<1。 5. The method for measuring light extraction efficiency and internal quantum efficiency of an LED chip according to claim 4, wherein: In the step S1, n groups of LED chips are prepared, where n≥3, and the smooth surface areas of the n groups of LED chips are S 11 、S 21 、S 31 …S n1 , the roughened surface areas of n groups of LED chips are S 12 、S 22 、S 32 …S n2 , where S 11 ≠S 21 ≠S 31 …≠S n1 , S 12 ≠S 22 ≠S 32 …≠S n2 .

6. The method for measuring light extraction efficiency and internal quantum efficiency of an LED chip according to claim 4, wherein: The ratio of the area of ​​the smooth surface in step S2 to the area of ​​the total light-emitting surface is x n By formula Calculated, where S n1 is the area of ​​the smooth surface of the nth group of chips, S n2 is the area of ​​the roughened surface; the area of ​​the smooth surface of n groups of LED chips accounts for x1, x2, x3...x n The ratio of the roughened surface area of ​​n groups of LED chips to the total light emitting surface area is 1-x1, 1-x2, 1-x3...1-x n .

7. The method for measuring light extraction efficiency and internal quantum efficiency of an LED chip according to claim 4, wherein: In step S3, the external quantum efficiency E of the LED chip at the same current density is n The measurement method is to apply a current I between the first electrode and the second electrode of the LED chip, and use a semiconductor analyzer to measure the light power P and the emission wavelength λ of the LED chip; according to the formula Calculate the external quantum efficiency E of the LED n , the actual external quantum efficiencies of n groups of chips are E1, E2, E3, ...E n .

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