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Description
With the rise of 5G technology and the popularization of mobile devices, more advanced photoelectric sensors are being used in our daily lives. In order to be better applied to mobile devices, the photosensitive area of these advanced photodetectors is getting smaller. However, these applications place increasingly higher requirements on the light-sensing performance of advanced photodetectors. The process of shrinking the photosensitive area brings the challenge of accurately measuring quantum efficiency. For example, under different wavelengths of the traditional focused beam spot, the focal shift caused by the dispersion of different wavelengths can reach the mm-level. It is difficult to focus all photons into the micrometer-level active area. Therefore, accurately measuring the full-spectrum quantum efficiency curve is challenging.
APD-QE adopts spatial light homogenizing technology and follows the ASTM standard āIrradiance Modeā test method, which has proven that it can accurately perform quantum efficiency and other key parameter measurements of advanced photodetectors. APD-QE can be combined with various advanced probe stations to deliver a complete testing solution for many advanced photodetectors, such as iPhone LiDAR and its variety of light sensors, Apple Watch blood oxygen light sensor, TFT image sensor, active pixel sensor (APS), high-sensitivity indirect conversion X-ray sensor, etc.
Introducing PEMā¢ (Photon-Energy Modulator), the revolutionary solution designed to elevate your quantum efficiency testing and spectral analysis to new heights. This innovative tool offers precise control over photon flux and energy, ensuring accurate and reliable results across various wavelengths.Ā
Challenges of Traditional QE Systems in the Testing of New Photodetectors:
- Most quantum efficiency systems on the market operate in āPower Mode.ā
- With the widespread popularity of mobile devices, advanced photodetectors such as APD, SPAD, ToF, etc., have miniaturized the light-receiving area of the device. The effective light-receiving area ranges from tens to hundreds of microns (10um ~ 200um).
- The āPower Modeā focusing light beam struggles to accurately measure these advanced small-area photodetectors due to:
- It is challenging to focus all photons into the effective light-receiving area at the micrometer level (which does not meet the requirements of Power Mode). This makes it difficult to obtain the absolute EQE.
- Overcoming measurement errors caused by optical dispersion and spherical aberration when focusing different colors of light is problematic. This results in an incorrect EQE spectrum curve.
- It is difficult to integrate probe stations.
Features
- Uniform light beam spot (āIrradiance Modeā) which complies with ASTM E1021
- A uniform light spot can overcome the problems of chromatic dispersion and aberration, accurately measuring the EQE curve of micrometer-level photodetectors compared to traditional focused beam spots.
- It can be paired with a variety of probe station systems for non-destructive and rapid testing.
- The integrated optics and test system improve system construction efficiency.
- One-key automatic test software provides automatic full spectrum calibration and measurement, enhancing work efficiency.
- Test characteristics:
ā External quantum efficiency EQE
ā Spectral response SR
ā I-V curve measurement
ā NEP spectrum measurement
ā D*spectrum measurement
ā Noise-current-frequency response graph (A/Hz-1/2; 0.01Hz~1,000Hz)
ā Flicker noise, Johnson Noise, Shot noise analysis
Enlitechās team of experts possesses extensive laboratory experience and technical knowledge, enabling them to guide customers in conducting precise tests both online and on-site. For instance, through detailed analysis of noise current frequency plots, Enlitech assists customers in identifying potential testing errors and optimizing test parameters, thereby enhancing the accuracy and reproducibility of their measurements.
Enlitech understands that in the field of optoelectronics, accurate testing is crucial for product development and quality control. Customers often face challenges with complex instrument calibration and unstable data when conducting tests such as noise current frequency, quantum efficiency (EQE), detectivity (D*), and noise equivalent power (NEP). Enlitech provides comprehensive solutions to address these pain points.
Metrics like EQE and D* directly impact the sensitivity and performance of photodetectors, which is particularly critical in high-tech fields such as semiconductors, communications, and aerospace. Accurate test data not only helps customers improve product quality but also reduces product development cycles and saves costs.
Enlitech
We Make Sensors Better.
Specification
Customized spot size and light intensity
APD-QE (Advanced Photodetector ā Quantum Efficiency Measurement System) manufactured by Enlitech has high light intensity and high spatial uniformity in the diameter of 25mm beam size and working distance of 200mm. The monochromatic light intensity of 530nm can exceed 82.97 uW/(cm2). The typical distribution of monochromatic light intensity is shown in the following figure.
The typicalĀ light intensityĀ measured by the APD-QE (Advanced Photodetector Quantum Efficiency Measurement System). The illumination beam size is 25mm diameter at the working distance of 200mm.
| WL (nm) | Full Width at Half Maximum (nm) | Uniformity U%=(M-m)/(M+m) | |
| 5mmĆ5mm | 3mmĆ3mm | ||
| 470 | 17.65 | 1.6% | 1.0% |
| 530 | 20.13 | 1.6% | 1.2% |
| 630 | 19.85 | 1.6% | 0.9% |
| 1000 | 38.89 | 1.2% | 0.5% |
| 1400 | 46.05 | 1.0% | 0.5% |
| 1600 | 37.40 | 1.4% | 0.7% |
Ā
The typicalĀ spatial uniformityĀ measured by the APD-QE (Advanced Photodetector Quantum Efficiency Measurement System). The illumination beam size is 25mm diameter at the working distance of 200mm.
Enlitech possesses optical design capabilities. We can provide a customized beam size and light intensity within a certain range. Please contact us with your requirements, and our professional team will assist you!
- Unique PEM (Photon-Energy Modulator)Constant-Photon control function
Enlitechās APD-QE (Advanced Photodetector ā Quantum Efficiency Measurement System) possesses the āConstant-Photonā control function (optional). With this function, users can perform measurements with the same number of photons at each wavelength. This Constant-Photon control function is a unique technology from Enlitech that other manufacturers cannot achieve.
Spectral test results under different constant photon flux conditions.
- By using Unique PEM (Photon-Energy Modulator) Constant-Photon control function (CP control mode), the variation of photon number can be < 1%.
Take the above figure as an example. The grey āNormalā line is the light intensity distribution of the xenon lamp light source at each wavelength, showing the spectral characteristics of the xenon lamp. If the CP control mode is used, different photon numbers at different wavelengths can be controlled to maintain consistent output characteristics. The orange line āCP=15000ā shows that the photon output at different wavelengths is 15,000 photons/s/um2.
- Examples of sample test and analysis
Sample of a-Si photo-FET
Under varying light intensity conditions, the tested spectral responses will differ. Please refer to the test results below
Ā
Sample of OPV or Perovskite PV
For OPV or perovskite PV samples, there is no difference in the test results between the general mode and the CP control mode. Please refer to the test results below.
| Measurable Parameters | Customizable Options |
|---|---|
| 1. Absolute light intensity calibration | 1.Customized dark box |
| 2. Spectral response measurement | 2.XYZ axis displacement platform |
| 3. External quantum efficiency measurement (EQE) | 3.Customized probe station integration service |
| 4. NEP (Noise Equivalent Power) spectrum | |
| 5. D* (detectivity) spectrum | |
| 6. Noise-current-frequency response chart (A/Hz-1/2) | |
| 7. Flicker noise, Johnson noise, Shot noise analysis | |
| 8. I-V curve measurement ā§Different light intensities for I-V curve measurement ā§Constant current/voltage, voltage/current vs. time testing ā§Under illumination conditions |
System Design
Ā
Integration of Uniform Light Homogenizer and Probe Station
- High Uniform Beam Spot
The use of exclusive patented Fourier optical elements to form a homogenization system can uniformize the spatial distribution of monochromatic light intensity. The light intensity distribution is measured in a 5 x 5 matrix within a 10mm x 10mm area, and the non-uniformity is less than 1% at 470nm, 530nm, 630nm, and 850nm. When measuring the light intensity distribution with a 10 x 10 matrix in a 20mm x 20mm area, the unevenness can be less than 4%.
- PDSW Software
PDSW software uses the new SW-XQE software platform, which can perform a variety of automated measurements, including EQE, SR, I-V, NEP, D*, frequency noise current graph (A/Hz1/2), noise analysis, etc.
- EQE Test
PDSW software can test wavelength of different monochromatic light and automatically perform EQE test for full spectrum.
- I-V Test
The software supports a variety of SMU controls, automatic light I-V test and dark state I-V test, and supports multi-data display.
- D* and NEP
Compared with other QE systems, APD-QE can directly measure and obtain D* and NEP.
- Frequency-Noise Current Curve
- Upgradable Software
Software can upgradable to FETOS software which can characterize 3-terminal or 4-terminal devices.
Integration with Probe Station
The APD-QE system can combine various types of Probe stations due to its exceptional optical system design. All the optical components of the full-wavelength spectrometer are integrated into the compact system. The monochromatic light is guided from the spectrometer to the probe stationās shielding box. The picture shows the MPS-4-S basic probe station components with a 4ā vacuum chuck and four probe micro-positioners with low-noise triaxial cables.
Customized Integration Solution Combining Probe Stage and Shielding Dark Box
- Customized Shielding dark box.
- Advanced Photodetector usually needs fast response response time. Therefore, the active area is usually small which requires probe station to make electrical contact.
- Ingegratable with different semiconductor analyzer such as 4200 or E1500.
Application
- Optical sensor in LiDARā InGaAs Photodiode/ SPAD
- Photosensor of APPLE Watch
- Photodiode-gated Transistor for high gain sensing and imaging
- High Photoconductivity Gain and Fill-Factor Optical Sensor
- Highly-sensitive indirect-conversion X-ray Detector characterization
- Silicon Photonics
Application 1: External quantum efficiency of Photodiode in iPhone 12ās LiDAR and other sensors
Application 2 : External quantum efficiency of Photodiode in Blood Oxygen sensor of APPLE Watch 6
The new Apple Watch Series 6 comes with a blood oxygen sensor and an accompanying app, providing more ways to monitor your heart and respiratory health.
The blood oxygen sensor is built into the back of the Apple Watch. It uses four sets of red, green, and infrared LED lights, along with four photodiodes. These devices can convert light into an electric current. The light hits the blood vessels in your wrist, and the photodiode measures the amount of light reflected back. Essentially, oxygenated and deoxygenated blood absorb red and infrared light differently, so the reflected light allows the Apple Watch to determine the color of your blood.
The APD-QE system is adopted to study and analyze the photodiode in the blood oxygen sensor, including the visible and infrared wavelength range.
APD-QE can provide the information of these photodiode:
- External quantum efficiency (300nm ~ 1700nm)
- SR (A/W)
- NEP and D*
- Frequency-Noise curve (A/Hz1/2)
- Noise Type
If you want to know more detail about the testing of optical sensors/ photodiodes of blood oxygen sensor in mobile devices, please be free to contactĀ EnlitechĀ immediately.
Application 3: Photodiode-gated Transistor for High Gain Sensing and Imaging
ććIn optical sensing and imaging applications, to enhance sensitivity and SNR, an APS (Active Pixel Sensor) incorporates a photodetector or a photodiode and several transistors to form a multi-component circuit. An essential unit, the in-pixel amplifier, also known as the source follower, is required. Since its inception, APS has evolved from a three-transistor circuit to a five-transistor circuit to address issues like blooming and reset noise. Besides APS, Avalanche Photodiodes (APD) and related products, such as Silicon Photomultipliers (SiPM), can also achieve high sensitivity. However, due to the necessity of a high electric field to initiate photomultiplication and impact ionization, the shot noise caused by the high field is significant in these devices.
Recently, the concept of a sub-threshold operating photodiode (PD) gated transistor device has been introduced. It can attain high gain without a high field or multi-transistor circuits. The gain is derived from the light-induced gate modulation effect, and to achieve this, sub-threshold operation is necessary. It also vertically integrates the PD and the transistor in a compact single-transistor (1-T) APS format to achieve high spatial resolution. This device concept has been implemented in various material systems, establishing it as a viable alternative technology for high-gain optical sensors.
APD-QE system is adopted to study and analyzing photodiode-gated amorphous silicon thin-film transistor.
- Photo transfer characteristics upon different light intensities.
- Threshold voltage change (ĪVth) as a function of light intensities.
- Transistor output characteristics with/without light exposure.
- External quantum efficiency and Gain of the photosensitive TFT as a function of wavelength.
(a)Ā Schematic structure of a-Si:H photodiode-gated LTPS TFT; (b)Ā Equivalent circuit diagram, showing APS with high SNR.
(a)Ā Micrograph of the pixel;Ā (b)Ā Micrograph of the partial array;Ā (c)Ā Photo of the image sensor chip.
If you want to test TFT type image sensor or know more detail about the testing, please be free to contact Enlitech immediately.
Photo transfer characteristics of 3-D dual-gate photosensitive a-Si:H TFT.
Gain of the photosensitive TFT as a function of wavelength at various photon fluxes.
Output characteristics of the TFT with and without light exposure.
System recommendation
- APD-QE system
- QE wavelength range 300~1100nm.
- Constant-photon/Constant-energy light control module.
- Highly uniform light beam homogenizer.
- Keysight B2912 semiconductor analyzer x 2
- Probe station: MPS-4-S probe station system with dark shielding box
- Software upgrade: FETOS-SW
Application 4: High Photoconductivity Gain and Fill-Factor Optical Active Pixel Sensor
Ā Ā Ā This Advanced PhotoDetector can be applied to optical active pixel sensors with āindirect conversion X-ray imagingā, āoptical fingerprint imagingā and ābiomedical fluorescence imaging.ā
Application 5: Highly-sensitive indirect-conversion X-ray Detector characterization
Highly-sensitive indirect-conversion X-ray Detector.
High resolution Backside illuminated (BSI) type X-ray detector panel.
High-sensitivity, large-area X-ray detectors are crucial for low-dose medical diagnostic X-ray imaging, such as digital radiography, fluoroscopy, and mammography. X-ray detection methods generally include direct conversion and indirect conversion. In direct conversion mode, photoconductors (for example, amorphous selenium) are used to directly convert X-ray photons into electric charges. In the indirect conversion mode, these charges are further read out by an amorphous silicon thin-film transistor (TFT). X-ray photons first pass through scintillators such as cesium iodide (CsI:Tl), bismuth germanate crystals (Bi4Ge3O12), or Gd2O2S:Tb phosphors, and then are usually detected by optical imaging sensors formed by amorphous silicon photodiodes and switching TFTs. In either mode, to achieve high sensitivity, signal amplification must be performed from the material/device level or the pixel circuit level. For example, highly sensitive direct X-ray photoconductors, such as perovskites, have recently been studied because they use photons more efficiently than commercially available direct conversion a-Se photoconductors, resulting in high quantum yields. However, perovskites have high leakage currents and also encounter stability/reliability issues. In X-ray imaging applications, reliability and stability are critical because thousands of scans must be performed every year. In the case of high-sensitivity indirect conversion X-ray detectors, since the quantum yield of many scintillators has reached its limit, however, due to the occupation area competition between the TFT circuit and the photodiode, the spatial resolution and fill factor are usually affected, so its sensitivity and high spatial resolution need to be weighed. Therefore, it is challenging to have a detector or pixel architecture that achieves both high sensitivity and high spatial resolution.
APD-QE system is adopted to study and analyzing the highly-sensitive indirect-conversion X-ray detector:
- Photo transfer characteristics upon different light intensities.
- Transistor output characteristics with/without light exposure.
- External quantum efficiency and Gain of the photosensitive TFT as a function of wavelength.
Light intensity dependence of threshold voltage change at differentĀ VTG(-12 V, -18 V, -24 V).
The orange line is the measured X-ray excited photoluminescence emission spectrum of CsI:Tl, the blue line refers to photo gain (Gph) of the photosensitive dual-gate TFT, and the purple line is the external quantum efficiency (EQE) curve of a classical p-i-n photodiode.
System recommendation
- APD-QE system
- QE wavelength range 300~1100nm.
- Constant-photon/Constant-energy light control module.
- Highly uniform light beam homogenizer.
- Keysight B2912 semiconductor analyzer x 2
- Probe station: MPS-4-S probe station system with dark shielding box
- Software upgrade: FETOS-SW
If you want to test indirective-conversion X-ray detectors or know more detail about the testing, please be free to contact Enlitech immediately.
Application 6: High Photoconductivity Gain and Fill-Factor Active Pixel Sensor (APS)
Active Pixel Sensor (APS)
ććAn a-Si:H pin photodiode and a low temperature polysilicon (LTPS) readout TFT are vertically stacked. By using a pin photodiode gated TFT architecture and operating the TFT in the sub-threshold range, the proposed APS device provides high fill factor and High internal photoconductive gain. Vertical integration results in a high fill factor (>70%) and enlarged photosensitive area in the pixel. In the photodiode gated TFT structure of the sensor, the output current is amplified by operating the TFT in a sub-threshold state. A weak wavelength-dependent light guide gain >10 is obtained at the visible light wavelength, thereby realizing large-area low-intensity light detection.
Large-area optical imaging and sensing equipment can be found in many applications that indirectly convert X-ray imaging, optical fingerprint imaging, and biomedical fluorescence imaging. APS with high gain and high fill factor has great potential for commercial applications.
APD-QE system is adopted to study and analyzing the active pixel sensor (APS):
- Photo transfer characteristics upon different light intensities.
- Transistor output characteristics with/without light exposure.
- External quantum efficiency and Gain of the photosensitive TFT as a function of wavelength.
Equivalent pixel circuit of (a) the hybrid active pixel sensor with SNR = AS/(N+n) and (b) a conventional passive pixel sensor with SNR = S/(N + n); A is the amplification factor, N is the noise from pixel, and n is the data line noise.
High Photoconductivity Gain and Fill-Factor Optical Sensor
Photon Transfer characteristics of the hybrid sensor.
Measured photoconductive gain at VBG = ā 6.3V and external quantum efficiency as a function of wavelength for various photon fluxes. External quantum efficiency of active pixel sensor was measured by APD-QE system.
System recommendation
- APD-QE system
- QE wavelength range 300~1100nm.
- Constant-photon/Constant-energy light control module.
- Highly uniform light beam homogenizer.
- Keysight B2912 semiconductor analyzer x 2
- Probe station: MPS-4-S probe station system with dark shielding box
- Software upgrade: FETOS-SW
If you want to test Active Pixel Sensor or know more detail about the testing, please be free to contact Enlitech immediately.
Customer Testimonials
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Publication
Xiao Wang,Zhulu Song,Haodong Tang,Yiwen Li,Huaying Zhong,Jiufeng Wu,Weichao Wang,Simin Chen,Wenjie Zhang,Fan Fang,Junjie Hao,Dan Wu,Peter MĆ¼ller-Buschbaum,Leifeng Cao,Zeguo Tang,Jun Tang,Lei Zhang,Kai Wang, and Wei Chen
First published: August 1, 2024 https://doi.org/10.1021/acsami.4c05201
ā¦ All of the SWIR PDs were characterized using PD-QE and APD-QE from ENLITECH Inc. for the EQE, responsivity, and detectivity characterization. A Keithly 4200 with extended PA was ā¦
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