System and method for measuring excess noise factor of avalanche photodetector
By constructing an excess noise factor measurement system for avalanche photodetectors, the accuracy problem of excess noise factor testing for mercury cadmium telluride avalanche detectors was solved, and the optimization and consistent evaluation of device performance were achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-16
- Publication Date
- 2026-03-27
AI Technical Summary
Existing technologies make it difficult to accurately test the excess noise factor of mercury cadmium telluride avalanche detectors, which limits the evaluation and optimization of device performance.
An avalanche photodetector excess noise factor measurement system is employed, comprising a Dewar, a blackbody, a dry cell, a spectrum analyzer, an amplifier, and a shielding device. The excess noise factor is calculated by measuring photocurrent, dark current, noise, and gain.
It enables accurate testing of the excess noise factor of mercury cadmium telluride avalanche detectors, provides a unified testing standard, and improves the accuracy and consistency of device performance evaluation.
Smart Images
Figure CN121740251A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present disclosure relates to the technical field of testing of semiconductor optoelectronic devices, and more particularly to a system and method for measuring excess noise factor of an avalanche photodetector. BACKGROUND
[0002] Mercury cadmium telluride is an important infrared detection material, and its forbidden band width can be continuously adjusted in the range of 1-1.65 eV with the change of component x, so it can realize the detection of all infrared wavebands. Mercury cadmium telluride infrared detector has a broad application prospect in the fields of aerospace, astronomy, meteorology, etc. Advanced mercury cadmium telluride infrared detection devices develop in the direction of large-scale, multi-dimensional detection, high-speed and intelligentization to meet the application requirements of improving the spatial spectral resolution and detection sensitivity of infrared systems.
[0003] With the continuous development of infrared detection technology, mercury cadmium telluride avalanche detector has become a research hotspot in the field of infrared detection due to its high sensitivity, low noise and wide spectral response. Mercury cadmium telluride detector uses avalanche multiplication effect to amplify the received signal, thereby realizing high-sensitivity detection of weak signals. The collision ionization process is mainly a random process, in addition to shot noise, the position of the initial carrier induced collision ionization event and the collision ionization path length also bring randomness. This causes the device gain to fluctuate around the average value, and this statistical distribution is called excess noise. The existence of this part of noise limits the performance of the detector. The excess noise factor (F) is a parameter that describes the difference between the noise introduced by the avalanche multiplication process in the avalanche detector and the ideal case (i.e. no additional noise). Therefore, as an important parameter for measuring the noise performance of mercury cadmium telluride avalanche detector, the accurate testing of the excess noise factor is the key to evaluating the performance of the avalanche detector, and it is also crucial for preparing and optimizing the process parameters of the avalanche detector. SUMMARY
[0004] In view of the above problems, the present disclosure provides an avalanche photodetector excess noise factor measurement optimization method. The specific technical solution is as follows:
[0005] An avalanche photodetector excess noise factor measurement system, comprising: a Dewar, a black body, a dry battery, a spectrum analyzer, an amplifier, a shielding device, and a source voltage meter; the Dewar is used to package a to-be-tested device to provide a low-temperature working environment and an electrode, the to-be-tested device comprising an avalanche photodetector chip; the Dewar and the to-be-tested device are placed in the shielding device, the black body is used to output steady light to the avalanche photodetector chip for testing; the dry battery is used to output a steady voltage to the avalanche photodetector chip for noise testing; and the avalanche photodetector chip is connected with the amplifier, and the spectrum analyzer is connected based on an alternating current path to form a noise testing link.
[0006] Preferably, the AC path comprises a high frequency transmission line.
[0007] An avalanche photodetector excess noise factor measurement method applied to the system, the method comprising:
[0008] Step 1, measure the photocurrent and dark current of the device under different bias voltages, determine the gain value of the avalanche photodetector chip under different target voltage values;
[0009] Step 2, measure the noise floor of the test system ;
[0010] Step 3, test the noise of the device under different blackbody irradiance intensities, and fit the calculation to obtain the initial noise under unit gain of the device ;
[0011] Step 4, test the noise of the device under different bias voltages, and obtain the noise value under different bias voltages ;
[0012] Step 5, according to the noise value measured under the bias voltage , the noise under unit gain of the device , and the gain under the bias voltage, calculate the excess noise factor under the gain .
[0013] Preferably, step one includes measuring the photocurrent and dark current of the device under different bias voltages, and calculating the gain of the device under different bias voltages using the formula , where is the photocurrent when the bias voltage is 0V, is the dark current when the bias voltage is 0V, and the gain calculation expression is .
[0014] Preferably, step two includes measuring the noise floor of the system without any external light source and power supply .
[0015] Preferably, step three includes testing the noise under different blackbody intensities without bias voltage, i.e. under unit gain; selecting a region with a relatively flat noise spectrum curve to take the average value as the shot noise under the corresponding blackbody irradiance intensity, i.e. under the corresponding photocurrent ; drawing a scatter plot with the photocurrent as the horizontal coordinate and the as the vertical coordinate, testing the noise under different blackbody intensities, and then performing linear fitting to obtain the slope k of the straight line; under unit gain, where, and is the noise and photocurrent when the unit gain is defined as a test system input impedance coefficient q is the charge quantum; according to the measured initial photocurrent , the initial noise of the device under unit gain is calculated .
[0016] Preferably, step four includes testing the noise under different bias voltages by applying a bias voltage through a dry battery, selecting a region with a relatively flat noise spectrum curve to take an average value as the shot noise under the corresponding voltage .
[0017] Preferably, in step four, for the short-wave APD device test, the blackbody irradiation is turned on throughout the process, and the blackbody power is fixed.
[0018] Preferably, step five includes calculating the excess noise factor under different bias voltages according to the noise values measured under the same bias voltage . .
[0019] Preferably, the shot noise is deducted from the noise floor .
[0020] The present application has the following beneficial effects:
[0021] 1. Core innovation empowerment test: the first to adapt to the test model of the intrinsic characteristics of mercury cadmium telluride material, targeted innovation, realize the whole process optimization.
[0022] 2. Fill the gap of industry standard: build a whole process test standard specification and evaluation system, provide a unified benchmark, solve the pain points of industry test data dispersion, unable to compare horizontally, promote technology exchange and industrialization.
[0023] In summary, the present application overcomes the key bottleneck of the existing mercury cadmium telluride avalanche photodetector excess noise factor test technology, and the technical achievements have significant innovation, practicality and industry leading nature. Not only can it directly improve the application efficiency of related high-end fields, but also can promote the technological progress of the entire industry, and has high popularization value and industrialization prospect. BRIEF DESCRIPTION OF DRAWINGS
[0024] The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of embodiments of the present disclosure with reference to the accompanying drawings, in which:
[0025] Figure 1 is a schematic diagram of an avalanche photodetector excess noise factor measurement system.
[0026] Figure 2 A flow chart for an avalanche photodetector excess noise factor measurement method.
[0027] Figure 3 A photocurrent graph for a mercury cadmium telluride shortwave APD device under room temperature background radiation.
[0028] Figure 4 A noise floor graph for a noise test system.
[0029] Figure 5 A graph of fitted photocurrent I-V curves and dry cell I-t read points in an example.
[0030] Figure 6 A graph of initial noise with no gain for fitted variable gain photocurrent in an example.
[0031] Figure 7 A noise power graph for varying bias in an example.
[0032] Figure 8 A graph of excess noise factor corresponding to fitted gain in an example. DETAILED DESCRIPTION
[0033] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other. In order to achieve the above-mentioned purpose, the technical solutions adopted by the present application are as follows.
[0034] The present application discloses an avalanche photodetector excess noise factor measurement optimization method, the measurement system used by the method is shown as Figure 1 The present application discloses an avalanche photodetector excess noise factor measurement optimization method, the measurement system used by the method is shown as
[0035] The present application discloses an avalanche photodetector excess noise factor measurement optimization method, the measurement system used by the method is shown as Figure 2 The present application discloses an avalanche photodetector excess noise factor measurement optimization method, the measurement system used by the method is shown as
[0036] Step 1: Measure the photocurrent of the device under different bias voltages. Dark current Using the formula Calculate the gain of the device under different bias voltages ,in It is the photocurrent when the bias voltage is 0V. This refers to the dark current when the bias voltage is 0V. If the device's dark current is much smaller than the photocurrent (by several orders of magnitude), then the effect of the dark current on the gain calculation can be ignored. The gain calculation expression is: When the noise of the bias test device is changed, the photocurrent under that bias is measured simultaneously to calculate the gain at that time. If it matches the gain curve, it proves that the gain assessment during the noise test is accurate.
[0037] Step 2: Measure the system's noise floor without any external light source or power supply. .
[0038] Step 3: Under no bias voltage, i.e., unity gain, test the noise at different blackbody intensities. Select the region with the flatter noise spectrum curve and take the average value as the corresponding blackbody irradiance, i.e., the corresponding photocurrent. shot noise ( Background noise needs to be reduced Plot the x-axis as photocurrent. The vertical axis is (unit The scatter plot of the signal is typically used to test noise at more than seven different blackbody intensities, followed by linear fitting to obtain the slope k of the straight line. At unity gain, ,in, and These are the noise and photocurrent at unity gain. Defined as the input impedance coefficient of a test system The noise spectrum analyzer converts the test results from units of... Convert to One system parameter in the calculation process, according to numerous actual test results, has a value close to 1; q represents the charge; based on the measured initial photocurrent... Calculate the initial noise of the device under unity gain. .
[0039] Step four involves testing the device noise under different bias voltages. Noise testing is susceptible to interference from the voltage source, so the current testing method utilizes a dry cell battery to apply the bias voltage. By applying the bias voltage with a dry cell battery, the noise at different bias voltages is tested, and the average value of the region with the flatter noise spectrum curve is taken as the shot noise at the corresponding voltage. (Shot noise) Background noise needs to be reduced ).
[0040] For short-wavelength APD devices, the photocurrent under room temperature background irradiation is only 1×10⁻⁶. -12 A around (e.g.) Figure 3 As shown), the corresponding initial noise is =3.2×10 -19 ×1×10 -12 =3.2×10 -31 Much lower than the background noise of the test system (10) -28 Magnitude, such as Figure 4 As shown in the figure, blackbody irradiation needs to be turned on throughout the process and the blackbody power needs to be fixed.
[0041] Step 5: Based on the noise value measured under the same bias voltage (unit Excess noise factor under different bias voltages calculate: .
[0042] To better understand, the contents of this disclosure are further illustrated below with reference to the embodiments, but this disclosure is not limited to the examples below.
[0043] Figure 5 It is a comparison between the gain test curve and the gain calculated from the photocurrent measured when the bias voltage is changed to test the noise. The gain points under different dry cell voltages can coincide with the gain curve, proving that the gain data is correct.
[0044] Figure 6 It is a fit As a result, noise was tested under different blackbody intensities, with the horizontal axis representing photocurrent. The vertical axis is The S-Frequency curves measured under different blackbody intensities were plotted on a single graph. The average value of the noise in the relatively flat region was taken as the corresponding photocurrent. shot noise ( Background noise needs to be reduced The subsequent fitted slope was... Initial photocurrent The noise at unity gain of the device is calculated:
[0045] ;
[0046] Figure 7These are noise test results under different bias voltages. The average value is taken from the region with the flatter noise spectrum curve, which is used as the shot noise at the corresponding voltage. (Shot noise) Background noise needs to be reduced ).
[0047] Figure 8 yes The factor calculation results are based on the noise values measured under the same bias voltage. (unit Excess noise factor under different bias voltages calculate: .
[0048] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.
Claims
1. A system for measuring the excess noise factor of an avalanche photodetector, characterized in that, include: Dewar, blackbody, dry cell battery, spectrum analyzer, amplifier, shielding device, and source voltage gauge; The Dewar is used to encapsulate the device under test (DUT) to provide a low-temperature operating environment and lead-out electrodes. The DUT includes an avalanche photodetector chip. The Dewar and the DUT are placed in a shielding device. The blackbody is used to output steady light to the avalanche photodetector chip for testing. The dry cell is used to output steady voltage to the avalanche photodetector chip for noise testing. The avalanche photodetector chip is connected to the amplifier and connected to the spectrum analyzer via an AC path to form a noise test link.
2. The system according to claim 1, characterized in that, in, The communication path includes a high-frequency transmission line.
3. A method for measuring the excess noise factor of an avalanche photodetector, applied to the system according to claim 1, characterized in that, The method includes: Step 1: Measure the photocurrent and dark current of the device under different bias voltages to determine the gain value of the avalanche photodetector chip under different target voltage values; Step 2: Measure the noise floor of the test system. ; Step 3: Test the noise of the device under different blackbody irradiation intensities, and calculate the initial noise of the device under unity gain. ; Step 4: Test the noise of the device under different bias voltages to obtain the noise values under different bias voltages. ; Step 5: Based on the noise value measured under bias voltage Noise at unity gain of the device And the gain under this bias voltage, the excess noise factor under this gain is calculated. .
4. The method for measuring the excess noise factor of an avalanche photodetector according to claim 3, characterized in that, Step one includes measuring the photocurrent of the device under different bias voltages. Dark current Using the formula Calculate the gain of the device under different bias voltages ,in It is the photocurrent when the bias voltage is 0V. This is the dark current when the bias voltage is 0V, and the gain calculation expression is: .
5. The method for measuring the excess noise factor of an avalanche photodetector according to claim 4, characterized in that, Step two includes measuring the system's noise floor without any external light source or power supply. .
6. The method for measuring the excess noise factor of an avalanche photodetector according to claim 4, characterized in that, Step three includes testing the noise at different blackbody intensities under no bias voltage, i.e., unity gain; selecting the region with a relatively flat noise spectrum curve and taking the average value as the corresponding blackbody irradiance, i.e., the corresponding photocurrent. shot noise Plot the x-axis as photocurrent. The vertical axis is The scatter plot was used to test the noise under different blackbody intensities, and then a linear fit was performed to obtain the slope k of the straight line; at unity gain, ,in, and These are the noise and photocurrent at unity gain. Defined as the input impedance coefficient of a test system q is the amount of electric charge; according to the measured initial photocurrent Calculate the initial noise of the device under unity gain. .
7. The method for measuring the excess noise factor of an avalanche photodetector according to claim 6, characterized in that, Step four involves applying a bias voltage using a dry cell battery to test the noise under different bias voltages, selecting the region with the flatter noise spectrum curve, and taking the average value as the shot noise at the corresponding voltage. .
8. The method for measuring the excess noise factor of an avalanche photodetector according to claim 7, characterized in that, In step four, when testing short-wavelength APD devices, blackbody irradiation is turned on throughout the process, and the blackbody power is fixed.
9. The method for measuring the excess noise factor of an avalanche photodetector according to claim 7, characterized in that, Step five includes determining the noise value measured under the same bias voltage. Excess noise factor under different bias voltages calculate: .
10. The method for measuring the excess noise factor of an avalanche photodetector according to claim 9, characterized in that, shot noise Middle reduction of background noise .