Method for rapidly measuring diffusion length of semiconductor carrier based on photocarrier radiation imaging

Abstract

The invention relates to the technical field of semiconductor material characteristic measurement, in particular to a semiconductor carrier diffusion length rapid measurement method based on photocarrier radiation imaging, which comprises the following steps of: focusing a continuous pumping laser light source of which the photon energy is greater than the forbidden bandwidth of a semiconductor, and irradiating to the surface of a semiconductor monocrystalline silicon material to be measured; excess free carriers are generated after being absorbed by a tested semiconductor monocrystalline silicon material, the free carriers can be diffused from a high-concentration position of a pumping area to a low-concentration position of a non-pumping area, and meanwhile, the free carriers are compounded in various modes such as defect non-radiative recombination and inter-band radiative recombination, so that the concentration of the free carriers is influenced. The diffusion length can be quickly obtained; the data processing is simple, and the uniqueness of the measurement result is high; the measuring device is simpler, the measuring speed is higher, and the sample cannot be damaged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor material property measurement, and particularly relates to a semiconductor carrier diffusion length rapid measurement method based on photo-carrier radiation imaging. BACKGROUND

[0002] The semiconductor carrier diffusion length is an important material parameter reflecting material quality and purity, and represents the average distance that the non-equilibrium minority carriers in the semiconductor can travel by diffusion before recombination, which is determined by carrier lifetime and mobility. In device applications, the diffusion length determines whether the photo-generated carriers or injected carriers can be effectively collected, thereby directly affecting the photoelectric conversion efficiency of solar cells, the current amplification capability of transistors, and the responsivity of photodetectors. Therefore, accurate measurement of the diffusion length is indispensable for material evaluation, process optimization, and device performance improvement.

[0003] The document with the patent publication number "CN1564315A" discloses a "semiconductor excess carrier diffusion length device and method", which injects excess carriers into the semiconductor using a pulsed light source, observes the second-order differential of the photoconductivity decay process with respect to time, and calculates the diffusion length of the semiconductor carriers according to the peak position and half-width. The disadvantage of this method is that it needs to make electrodes on the surface of the measured sample to apply an electric field, and needs a nanosecond-level pulsed light source and a low-temperature refrigeration device, which increases the complexity of the measurement, has high measurement cost, and causes damage to the measured sample, affecting the accuracy of the measurement results.

[0004] The document "B. Fluegel, K. Alberi, et al. Carrier decay and diffusion dynamics in single-Crystalline CdTe as seen via microphotoluminescence. Phys. Rev. Applied 2, 034010(2014)" measures the carrier diffusion length of the semiconductor CdTe material through a "spatial and temporal resolution photoluminescence technology", which analyzes and calculates the carrier diffusion coefficient by analyzing the photoluminescence imaging data at different times D , calculates the carrier lifetime according to the photoluminescence signal intensity data at different times τ , and finally obtains the carrier diffusion length value through the formula . The disadvantage of this method is that it needs a picosecond or femtosecond pulsed laser for pumping and a nanosecond time-resolved camera for high-precision time resolution detection, which has high measurement cost.

[0005] The document "A. Mandelis, J. Batista, and D. Shaughnessy. Infrared photocarrier radiometry of semiconductors: Physical principles, quantitative depth profilometry, and scanning imaging of deep subsurface electronic defects. Phys. Rev. B 67, 205208 (2003)" proposes to measure the carrier lifetime, diffusion length and other parameters of semiconductor materials by frequency scanning photo carrier radiation technology, and then obtain the carrier diffusion length value through formula The disadvantage of the method is that the modulation frequency domain of the pump light needs to be scanned, the measurement speed is slow, and a complex mathematical model needs to be established for data fitting, and the uniqueness of the measurement result is not high. SUMMARY

[0006] The present application provides a semiconductor carrier diffusion length fast measurement method based on photo carrier radiation imaging to solve the problems of complex measurement process and inaccurate measurement results in the prior art.

[0007] To solve the problems in the prior art, the technical scheme of the present application is as follows: a semiconductor carrier diffusion length fast measurement method based on photo carrier radiation imaging, characterized by comprising the following steps in sequence: Step one, focusing the continuous pump laser and irradiating it to the surface of the measured semiconductor sample; Step two, imaging the pumped area by an imaging camera and recording the intensity value S0( r ) of the imaging signal, wherein r is the distance from the center position of the pump light; Step three, performing smoothing filter processing on the measured signal data S0( r ) to obtain data S( r ), intercepting the data S( r ) of the non-pumped area, wherein ; Step four, calculating the intercepted data S( r ) in step three by using a theoretical model to obtain the carrier diffusion length of the measured semiconductor material: The mathematical expression of the theoretical model is In the formula, L is the carrier diffusion length, ris the distance from the center position of the pump light, S( r ) is the data of the signal obtained by the smoothing filter processing at a position far greater than the pump light radius, and R is the pump light radius.

[0008] Further, the photon energy of the pump laser is greater than the band gap width of the measured semiconductor.

[0009] Further, the response wavelength of the imaging camera covers the wavelength of the photo-carrier radiation signal.

[0010] Compared with the prior art, the present application has the following advantages: 1) The present application provides a new measurement idea based on a phenomenon that due to the diffusion of carriers, the excess carriers generated in the pump light region will diffuse to the adjacent non-pump region, resulting in the generation of excess carriers in the non-pump region, and the greater the diffusion length, the greater the carrier concentration diffused to the non-pump region, and the stronger the photo-carrier radiation signal. Therefore, when measuring the carrier diffusion length of the semiconductor, only the image gray data at the non-pump region in the imaging signal needs to be analyzed and calculated, and the diffusion length can be quickly obtained. 2) When measuring the carrier diffusion length of the semiconductor, the present application does not need multi-parameter fitting processing, but only needs to intercept the imaging data of the non-pump region to obtain the carrier diffusion length, the data processing is simple, and the uniqueness of the measurement result is high. 3) Compared with the traditional time domain and frequency domain measurement methods, the present application does not need an ultrafast laser source and a fast response photoelectric detector when measuring the carrier diffusion length of the semiconductor, and does not need to be in direct contact with the sample, the measurement device is simpler, the measurement speed is faster, and the sample will not be damaged. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a structural schematic diagram of the measurement device of the present application; Figure 2 is the photo-carrier radiation imaging result of the experimental measurement of the semiconductor silicon wafer according to the present application; Figure 3 is the photo-carrier radiation imaging result of the experimental measurement of the semiconductor silicon wafer according to the present application; Figure 2 in r > 2.5 a The carrier diffusion length result obtained after processing and calculating the data of

[0012] The reference signs are as follows: 1-pump laser source, 2-focusing lens, 3-beam splitter, 4-measured semiconductor single crystal silicon, 5-sample holder, 6-long wave pass filter, 7-imaging camera, 8-computer. DETAILED DESCRIPTION

[0013] In order to make the objects, technical solutions and advantages of the present application clearer, further detailed description will be made to the present application in combination with the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0014] The principle of the present application is: The continuous pump laser with photon energy greater than the band gap of the semiconductor is focused and irradiated to the surface of the semiconductor sample, and the measured semiconductor sample absorbs the pump laser to generate excess free carriers, which diffuse from the high concentration area of the pump region to the low concentration area of the non-pump region, and are recombined through various ways such as defect non-radiative recombination and interband recombination, thereby affecting the concentration of free carriers . Considering the lateral diffusion and defect recombination process of the free carriers, it satisfies: (1) Wherein, G is the carrier generation term related to the radius of the pump light, a is the carrier diffusion coefficient, and D is the carrier lifetime, d is the differential symbol, represents the second-order differential, represents the first-order differential.

[0015] For the non-pump region, i.e. the position far from the center of the pump light r , it satisfies: (2) The free carriers generated by the pump light are radiated through interband recombination, i.e. the photo-carrier radiation signal S( r ), and the signal strength is proportional to the carrier concentration when the injection is low, C is the proportional coefficient. The photo-carrier radiation signals at different lateral positions r are collected by the imaging camera 7, and finally the diffusion length of the measured semiconductor sample is calculated by the computer 8 according to the formula: (3)

[0016] The measuring device used in the present application is a common device for measuring the carrier recombination characteristics (such as carrier lifetime) of the semiconductor, which is described in detail in the following reference: Figure 1 ​The measured semiconductor sample in this embodiment is a measured semiconductor single crystal silicon 4. The output beam of the pump laser source 1 is irradiated to the front surface of the measured semiconductor single crystal silicon 4 through the focusing lens 2 and the beam splitter 3 after being reflected by the beam splitter 3; the photons of the light carrier radiation generated by the light excitation in the measured semiconductor single crystal silicon 4 are detected by the imaging camera 7 after penetrating through the front surface of the sample and the long-wave pass filter 6, so as to obtain the light carrier radiation imaging signal; the computer 8 is used for storing and processing the light carrier radiation imaging signal data of the imaging camera 7. The long-wave pass filter 6 is placed in front of the imaging camera 7, which is used for filtering the scattered light and background stray light of the pump light entering the imaging camera 7.

[0017] The pump laser source 1 is selected as a semiconductor laser with a wavelength of 830 nm, and the photon energy generated by the pump laser is 1.49 eV, which is greater than the band gap width <1.1 eV of the measured semiconductor single crystal silicon 4; the imaging camera 7 is an InGaAs near-infrared camera with a response wavelength range of 800-1700 nm.

[0018] A carrier diffusion length rapid measurement method, which comprises the following steps in sequence: Step one, the continuous pump laser source 1 is focused by the focusing lens 2 and irradiated to the sample surface of the measured semiconductor single crystal silicon 4, and the measured semiconductor single crystal silicon 4 material absorbs the pump laser to generate excess free carriers. Due to the existence of concentration difference, the free carriers diffuse to the adjacent non-pumped area, and are finally compounded in multiple ways, including radiative recombination and non-radiative recombination, to achieve a steady state distribution; Step two, the near-infrared imaging camera 7 is used to collect and image the radiative recombination light signal, i.e. the light carrier radiation signal S0( r ) of the pumped area and the adjacent area, and the long-wave pass filter 6 is placed in front of the lens to filter out the influence of the scattered light and background stray light of the pump laser source 1; Step three, the light carrier radiation imaging signal S0( r ) collected by the imaging camera 7 is processed by the computer 8 for smoothing filtering to remove data noise, so as to obtain the signal S( r ) filtered from the data noise, and then the data far away from the pump light radius a (i.e. the data far away from the pump light radius a ) is intercepted. The reason for intercepting the measurement data far away from the pump light radius a is to meet the prerequisite condition of formula (2) in the principle model, so as to reduce the influence of the carrier radiation directly excited by the pump light on the calculation result of the diffusion length.

[0019] Step four, the theoretical formula is used to calculate the data, so as to obtain the carrier diffusion length L of the measured semiconductor single crystal silicon 4 material.r )。

[0020] The specific measurement steps of the present application are as follows: 1. Fix the measured semiconductor single crystal silicon 4 on the sample holder 5, turn on the computer 8, the pump laser light source 1, and the imaging camera 7; 2. Adjust the pump laser light source 1, the focusing lens 2, and the beam splitter 3 so that the pump laser light source 1 is focused to the position of the detected area on the surface of the measured semiconductor single crystal silicon 4; 3. Use the imaging camera 7 with a long-wave pass filter 6 placed in front of the lens to detect the optical carrier radiation signal of the measured semiconductor single crystal silicon 4, and record the optical carrier radiation imaging signal S0( r ) through the computer 8; 4. Perform smoothing filter processing on the measured signal S0( r ) through the computer 8 to obtain the smoothed data S( r ), then intercept the data in S( r ) far from the pump light radius a , and finally calculate the data using the theoretical formula to obtain the carrier diffusion length of the measured semiconductor single crystal silicon 4 material at different positions of the measured semiconductor single crystal silicon 4 material. r

[0021] Figure 2 is the optical carrier radiation imaging result of the measured semiconductor single crystal silicon 4 according to the present application. The measured semiconductor single crystal silicon 4 is a N type single-side polished Czochralski single crystal silicon with a thickness of 525 μm and a resistivity of 7-10 Ω·cm. Since the light intensity of the pump light is Gaussian distribution, the optical carrier radiation signal strength is the largest at the center position of the pump light, and the farther the distance from the center position, the lower the signal strength. Sampling the data at the white dashed line position in the figure can obtain the optical carrier radiation signal strength when the distance from the pump light center position changes.

[0022] Figure 3 is the Savitzky-Golay smoothing filter of the data at the white dashed line position in Figure 2 , and the order of the filter function is set to 3 here. The data r > 2.5 a ​The carrier diffusion length results were obtained after calculating the data. It can be seen that the carrier diffusion length does not change much in the range of 80-160 μm from the pump light center, but increases beyond 160 μm. This is because the concentration of excess carriers decreases with distance from the pump region, and radiative recombination and Auger recombination play a weaker role in the overall recombination process. Simultaneously, reduced carrier scattering leads to an increase in the diffusion coefficient, ultimately resulting in an increased diffusion length. This is consistent with theoretical predictions of carrier recombination and diffusion mechanisms. Statistical analysis of the data in the figure shows the carrier diffusion length at pump light powers of 25 mW, 33 mW, 40 mW, and 49 mW. L The carrier diffusion lengths for the above different powers are 57.4 μm, 55.5 μm, 53.0 μm, and 53.5 μm, respectively. L The average value is 54.8 μm, so the carrier diffusion length of the tested semiconductor single crystal silicon 4 material can be quickly measured by this method.

[0023] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A rapid measurement method for semiconductor carrier diffusion length based on photocarrier radiation imaging, characterized in that: The steps are as follows: Step 1: Focus the continuous pump laser and irradiate the surface of the semiconductor sample to be tested; Step 2: The imaging camera images the pumped area and records the intensity value S0 of the imaging signal. r ),in r This is the distance from the center of the pump light; Step 3: Measure the signal data S0 ( r The data S is obtained by performing smoothing filtering. r ), extract the data S( from the non-pumping region) r ),in ; Step 4: Use the theoretical model to analyze the data S(t) extracted in Step 3. r The carrier diffusion length of the tested semiconductor material is calculated as follows: The mathematical expression of the theoretical model is as follows:

2. In the formula, L The carrier diffusion length, r S is the distance from the center of the pump light. r The signal data is obtained by smoothing and filtering at a location much larger than the pump light radius. a The radius of the pump light.

3. The method for rapid measurement of semiconductor carrier diffusion length based on photocarrier radiation imaging according to claim 1, characterized in that: The photon energy of the pump laser is greater than the bandgap of the semiconductor being tested.

4. The method for rapid measurement of semiconductor carrier diffusion length based on photocarrier radiation imaging according to claim 1, characterized in that: The response wavelength of the imaging camera covers the wavelength of the photocarrier radiation signal.

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