CN102156135A - Measuring method and device of laser damaged silicon-based detector - Google Patents

Abstract

The photodetector is the core component of the photoelectric detection system. In some special occasions, the photoelectric sensor is often used in conjunction with the laser light source, so there is inevitably the problem of laser damage to the photoelectric sensor. The invention belongs to the field of photoelectric testing and provides a measurement method and device for laser damage silicon-based detectors. According to the changes of the surface morphology, photocurrent, dark current and responsivity of the detector before and after strong laser irradiation, the degree of laser damage to the detector can be judged. Previous studies on laser irradiation detectors mainly focused on the damage threshold and damage mechanism, and the quantitative research on the changes of dark current, photocurrent and responsivity in the process of detector damage has not been reported. The invention can detect the changes of electrical parameters and surface topography during the damage process of the detector on-line, has the advantages of comprehensiveness, accuracy and convenience, and is suitable for the damage detection of silicon-based unit detectors and the damage mechanism research of laser-induced detectors. It can be applied to laser processing, optical component quality inspection, laser development and other fields.

Description

Method and device for measuring laser damage to silicon-based detectors

technical field

The invention relates to a measurement method and device for laser damage silicon-based detectors, which can be used for photoelectric testing, and the application fields include the development of detectors, laser processing, scientific research and other fields.

Background technique

Photodetectors are the core components of photoelectric detection systems and are widely used in military, industrial, medical and other fields. In some special occasions, photoelectric sensors are often used in conjunction with laser light sources, so there is inevitably a problem of laser damage to photoelectric sensors. After the detector is damaged by strong laser light, its performance will change, manifested as a decrease in responsivity and an increase in dark current.

Scholars at home and abroad have done a lot of theoretical and experimental work on strong laser irradiation detectors, mainly focusing on the damage threshold and damage mechanism of laser irradiation detectors, and the photocurrent, dark current and responsivity of detectors after damage Changes are rarely studied. It is of great significance to master the change rule of the performance of laser-induced detector damage to study the damage mechanism of laser-irradiated detectors and improve the ability of detectors to resist laser damage.

The invention provides a set of measurement method and device for laser damage silicon-based detectors, adopts CCD imaging technology to obtain detector surface topography images before and after strong laser irradiation, uses current detection technology to measure photocurrent, dark current and The change of the responsivity of the detector is used to determine the damage of the laser to the detector according to the change of the surface topography and response performance. The experimental device is accurate, simple and easy to operate, and can monitor the surface damage of the laser irradiation detector in real time, and is suitable for the research on the damage effect of the laser irradiation silicon-based unit detector.

Contents of the invention

Studying the relationship between the damage degree of the detector and the change of electrical properties under strong laser irradiation is of great significance for studying the damage mechanism of the laser irradiation detector and improving the anti-laser damage ability of the detector. The invention provides a set of measurement methods and devices for visually detecting the surface topography, photocurrent and dark current of a detector after being damaged by laser. The device includes a laser irradiation system, a CCD imaging system, and a current detection system.

The laser irradiation system includes a Nd:YAG laser (1), a laser attenuator (2), a beam splitter (3), a laser energy meter (4), and a converging lens (5). The laser light emitted by the Nd:YAG laser is vertically irradiated on the surface of the detector through the laser attenuator, the beam splitter and the converging lens. The attenuator can adjust the energy of the incident laser, and the spectroscope and energy meter can monitor the energy of the incident laser in real time. The sample is fixed on the adjustment frame, which can be adjusted conveniently.

The current detection system consists of a He-Ne laser (8), an attenuator (9), a test circuit (10) and a photoelectric galvanometer (11). The detector works according to the internal photoelectric effect. When the incident laser power is not too large, the detector works in the linear region. The responsivity of the detector to the incident light is an important index of the photodetector, which is related to the wavelength of the incident light, that is, under the optical power radiation of a certain wavelength λ light, the output voltage V(λ) and current I(λ ) are different, so there are voltage spectral responsivity R _V and current spectral responsivity R _I , denoted as

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; V</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula, P(λ) is the incident light power at the wavelength λ; V(λ) is the output signal voltage of the photodetector under the action of the incident light power P(λ), and I(λ) is the photodetector at the incident light power P The current signal under the action of (λ). In the experiment, the He-Ne laser is used as the reference light, and the responsivity of the detector can be obtained by measuring the photocurrent of the detector to the He-Ne laser. After the detector is damaged by laser, the dark current increases and the responsivity decreases. Therefore, comparing the change of the detector responsivity before and after the damage can determine the damage of the detector.

The CCD imaging system comprises a white light diode (12), an imaging lens (13), an area array CCD (14) and a computer (15). The white light diode is about 5cm away from the detector, and the angle between it and the detector is about 30°C, and the angle between the He-Ne laser and the detector is about 25°C. By adjusting the distance between the detector sample, lens and CCD, the detector can form a clear image on the surface of the CCD. The image of the surface topography of the detector is stored by the computer. After strong laser irradiation, record the surface topography picture of the detector again, and compare it with the image before laser irradiation to determine the damage of the detector.

Description of drawings

Accompanying drawing 1 is the schematic diagram of laser-induced photodetector damage multi-parameter measurement method and device;

Accompanying drawing 2 is photocurrent and dark current test circuit;

Accompanying drawing 3 is the change of detector dark current under the laser irradiation of different power densities;

Accompanying drawing 4 is the change of detector responsivity under the laser irradiation of different power densities;

Accompanying drawing 5 is the photo of the surface topography of the detector after being irradiated by laser with a power density of 3.53×10 ⁷ w/cm ² ;

Attached Figure 6 is a picture of the surface morphology of the detector after being irradiated by a laser with a power density of 3.66×10 ⁸ w/cm ² ;

Accompanying drawing 7 is the photo of the surface topography of the detector after being irradiated by laser with a power density of 3.92×10 ⁸ w/cm ² ;

Figure 8 is a picture of the surface topography of the detector after being irradiated by a laser with a power density of 4.51×10 ⁹ w/em ² .

Detailed ways

Implementation example: Taking silicon-based PIN photodetector (model GT102, photosensitive surface diameter 2mm) as an example, study the surface morphology, photocurrent, dark current and Changes in responsivity, and analyze the relationship between detector performance changes and damage levels.

As shown in Fig. 1, the output laser power of the He-Ne laser (8) after passing through the attenuator (9) is 56uw. At this time, the silicon-based PIN photodetector works in the linear region. The photocurrent value of the detector measured by the photogalvanometer (11) is 11.76uA, the responsivity of the detector before damage is 0.21uA/uw, and the measured dark current value of the detector is 0.001nA. Adjust the white light diode (12), the imaging lens (13) and the area array CCD (14), so that the detector sample is imaged on the CCD, and stored with a computer. The Nd:YAG laser (1) is irradiated on the surface of the sample (6) through the attenuator (2), the beam splitter (3), and the converging lens (5), and coincides with the He-Ne laser spot. Adjust the laser attenuator so that the incident laser energy increases gradually from small to large. If the detector is damaged under a single pulse irradiation, replace the sample and repeat the above experiment, and you can get saturation, mild damage, moderate damage, and severe damage of the detector under a single laser irradiation with different power densities. After the detector is damaged, the surface topography image is stored, and the photocurrent and dark current values of the detector are measured again, and compared with the original data, the damage of the detector is analyzed.

Figure 3 and Figure 4 describe the changes of the dark current and responsivity of the detector under strong laser irradiation. It can be seen from the figure that after the laser power density exceeds 3.54×10 ⁴ w/cm ² , the detector is in a saturated state, the surface morphology does not change, and the dark current, photocurrent and responsivity do not change.

When the incident laser power density reaches 3.53×10 ⁷ w/cm ² , the surface of the detector is slightly damaged after laser irradiation, as shown in Figure 5, the surface anti-reflection coating is damaged, resulting in the The light transmittance decreases, the dark current increases by 0.004uA, and the responsivity decreases by 3.65%.

When the incident laser power density reaches 3.66×10 ⁸ w/cm ² , a large area of damage occurs on the detector surface after laser irradiation. As shown in Figure 6, the damaged area of the surface layer is enlarged, and slight damage occurs inside the photosensitive surface. At this time, the dark current changes significantly, increasing by 0.414uA, and the responsivity also changes significantly, decreasing by 12.3%.

When the incident laser power density reached 3.92×10 ⁸ w/cm ² , after laser irradiation, serious damage appeared on the detector surface. As shown in Figure 7, the damage area is larger and the damage pit is deeper. At this time, the photosensitive surface of the detector was damaged, the dark current increased by 12.78uA, and the responsivity decreased by 18.11%.

When the incident laser power density reaches 4.44×10 ⁹ w/cm ² , the detector is more severely damaged after strong laser irradiation. As shown in Figure 8, the damage area is larger, the damage pit is deeper, and the photosensitive area is severely damaged, resulting in partial breakdown of the PN junction. At this time, the dark current increases sharply, reaching 2300uA, far exceeding the photocurrent of the detector. value, at this time the detector has lost its detection capability.

From the above analysis, it can be seen that the device of the present invention can monitor the whole process of the detector being damaged by strong laser in real time, and at the same time, can detect the changes of dark current/photocurrent and responsivity under different damage degrees, which has great impact on the analysis of laser The damage mechanism of the detector is of great significance.

Claims (14)

1. A method and device for measuring laser damage to a silicon-based detector, comprising a laser irradiation system, a CCD imaging system, and a current detection system. The laser irradiation system can output strong lasers with different power densities to irradiate the detector; the current detection system can detect the photocurrent and dark current of the detector to the reference light; the CCD imaging system can analyze the surface morphology of the detector before and after laser damage for imaging. By comparing the surface morphology and response performance of the detector before and after laser irradiation, the damage to the detector by the strong laser is judged. 2. laser irradiation system according to claim 1, is characterized in that, by Nd:YAG laser (1), laser attenuator (2), beam splitter (3), laser energy meter (4), converging lens ( 5), sample (6) and three-dimensional adjustment frame (7). By adjusting the attenuator, lasers with different power densities can be output, and by adjusting the distance from the sample to the converging lens, the size of the laser spot irradiated on the sample can be changed. 3. The current detection system according to claim 1, characterized in that, comprising a He-Ne laser (8), a test circuit (9) and a sensitive galvanometer (10). 4. CCD imaging system according to claim 1, is characterized in that, comprises white light diode (11), imaging lens (12), area array CCD (13) and computer (14). 5. The laser irradiation system according to claim 2, characterized in that, the Q-switched Nd:YAG laser (1) has a wavelength of 1064nm, a pulse width of 9ns, a repetition rate of 10Hz, and a single pulse maximum laser energy of 500mJ. 6. laser irradiation system according to claim 2, is characterized in that, laser attenuator (2) is made of the attenuation lens of one group of neutral density, and lens diameter is 50mm, maximum attenuation 80db, minimum attenuation multiple 1.07db, Through the combination of different attenuation sheets, the laser output energy can be gradually increased from small to large. 7. The laser irradiation system according to claim 2, characterized in that the model of the laser energy meter (4) is NIM-E1000 laser energy meter. The resolution is 0.4mJ, the measurement uncertainty is 4%, and the applicable wavelength is 1064nm. 8. The laser irradiation system according to claim 2, characterized in that the diameter of the converging lens (5) is 25mm, and the focal length is 125mm. 9. The current detection system according to claim 3, characterized in that the power of the He-Ne laser (8) is 5mw. 10. The current detection system according to claim 3, characterized in that the reverse bias voltage of the test circuit (10) is 40V, and the capacitors of 47 μF and 0.1 μF act as filters, see Figure 2 for details. 11. The current detection system according to claim 3, characterized in that the precision of the photoelectric galvanometer (11) is 10 ^-9 A. 12. CCD imaging system according to claim 4, is characterized in that, the power of white light diode (12) is 0.1mw, operating current 20mA, the distance of diode to sample surface is about 6cm, the distance between diode and detector surface normal The included angle is between 25-30°C. 13. CCD imaging system according to claim 4, is characterized in that, the focal length of imaging lens (13) is 70mm, and aperture is the imaging lens of 25mm. 14. The CCD imaging system according to claim 4, characterized in that the total pixels of the CCD (14) are (537(H)×505(V)).

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