Advanced PhotoDetector - Quantum Efficiency System
With the rise of 5G technology and popularization mobile devices, more and more advanced photoelectric sensors are used in our daily lives. In order to be better applied to mobile devices, the photosensitive area of these advanced photodetector is getting smaller and smaller. However, these applications place higher and higher requirements on the light sensing performance of advanced photodetectors. In the process of shrinking the photosensitive area, it also brings the challenge of accurate measurement of quantum efficiency. For example, under different wavelengths of the traditional focused beam spot, the focal shift caused by the dispersion of different wavelength can reach mm-level. It is difficult to focus all photons into the micrometer-level active area. Therefore, it is hard to accurately measure the full-spectrum quantum efficiency curve.
APD-QE adopts the spatial light homogenizing technology and follows the ASTM standard “Irradiance Mode” test method, which is proven that it can accurately perform quantum efficiency and other key parameter measurements of advanced photodetectors. APD-QE can combine with various advanced probe stations to deliver a complete testing solution for many advanced photodetectors, such as iPhone LiDAR and a its variety of light sensors, Apple Watch blood oxygen light sensor, TFT image sensor, active active pixel sensor (APS), high-sensitivity indirect conversion X-ray sensor, etc
- Most of the quantum efficiency systems on the market are “Power Mode.”
- 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 of microns to hundreds of microns (10um ~ 200um).
- The “Power Mode” focusing light beam is hard to accurately measure the advanced small-area photodetectors due to :
- It is difficult to completely focus all photons into the effective light-receiving area in micrometer level (cannot meet the requirements of the Power Mode) => The absolute EQE is hard to be get.
- It is difficult to overcome measurement errors caused by optical dispersion and spherical aberration when focusing different color of light. =>The EQE spectrum curve is incorrect.
- Difficult to integrate probe stations.
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Features
- Uniform light beam spot (“Irradiance Mode”) which complies conforms to ASTM E1021
- Uniform light spot can overcome the problems of chromatic dispersion and aberration, which can accurately, compared to traditional focused beam spot, measure the EQE curve of micrometer-level photodetectors.
- It can be matched with a variety of probe station systems to achieve non-destructive and rapid testing.
- The integrated optics and test system improve the efficiency of system construction.
- One-key automatic test software, automatic full spectrum calibration and measurement, high work efficiency.
- Test characteristics:
– External quantum efficiency EQE
– Spectral response SR
– I-V curve measurement
– NEP spectrum measurement
– D*spectrum measurement
– Noise-current-frequency response graph (A/Hz-1/2; 0.01Hz~1,000Hz)
– Flicker noise, Johnson Noise, Shot noise analysis
Enlitech’s Exclusive Testing Technology
Customized spot size and light intensity
APD-QE (Advanced Photodetector – Quantum Efficiency Measurement System) manufactured by Enlitech has high light intensity and high spatial uniformity in the diameter of 25mm 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 typical light intensity 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) | |
| 5mm×5mm | 3mm×3mm | ||
| 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% |
The typical spatial uniformity 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 has the optical design capabilities. We can provide the customized beam size and light intensity within a certain range. Please contact us with your needs and our professional team will assist you!
Constant-Photon control function
Enlitech’s APD-QE (Advanced Photodetector – Quantum Efficiency Measurement System) possesses the control function of “Constant-Photon” (optional). Using this function, users can do the measurement with same photon numbers at each wavelength. This Constant-Photon control function is Enlitech’s unique technology which other manufacturers cannot achieve.
Spectral test results under different constant photon flux conditions.
By using Constant-Photon control function (CP control mode), the variation of photon number can be < 1%.
Take the above figure as an example. The gray Normal 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 CP=15000 shows that the photons output at different wavelengths is 15,000 photons/s/um2.
Examples of sample test and analysis
Sample of a-Si photo-FET
Under different conditions of light intensity, the tested spectral responses will be different. Please refer to the test results below.
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.
System Design
Specification
Main system:
● Quantum Efficiency Testing System
– 300nm ~ 1100nm (expandable to 2500nm)
● Software:
– PDSW software
– Upgradable to FETOS-SW (3T or 4T devices)
● Probe station system (option)
– 4” standard probe station (MPS-4-S)
● Customized integration solution combining probe stage and shielding dark box.
Integration of Uniform Light Homogenizer and Probe Station
High Uniform Beam Spot
The use of the exclusive patented Fourier optical elements to form homogenization system can uniformize the spatial distribution of the monochromatic light intensity. The light intensity distribution is measured at 5 x 5 matrix in an area of 10mm x 10mm, and the un-uniformity is less than 1% at 470nm, 530nm, 630nm, and 850nm. When measuring the light intensity distribution with a 10 x 10 matrix in an area of 20mm x 20mm, 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
APD-QE system can combine many kind of Probe stations due to its outstanding optical system design. All the optical components of full-wavelength spectrometer are integrated in the compact system. The monochromatic light is guided from spectrometer to the probe station shielding box. The picture shows MPS-4-S basic probe station components with 4” vacuum chuck and 4 probe micro-positioners with low noise triaxial cables.
The microscope of probe station is integrated and be switched to the position of the device under test with manual slider. The monochromatic light homogenizer is “pinned” at the designed position after using slider bar. The microscope image can be displayed on the screen which is convenient for users to make the good contact.
Customized Integration Solution Combining Probe Stage and Shielding Dark Box
A. Customized Shielding dark box.
B. Advanced Photodetector usually needs fast response response time. Therefore, the active area is usually small which requires probe station to make electrical contact.
C. Ingegratable with different semiconductor analyzer such as 4200 or E1500.
Application
- Optical sensor in LiDAR
– 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 12’s 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 to give you 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 and four photodiodes, these devices can convert light into electric current. The light hits the blood vessels on your wrist, and the photodiode measures the amount of light reflected back. Basically, oxygenated and deoxygenated blood absorb red and infrared light in different ways, so the reflected light allows Apple Watch to determine the color of your blood.
APD-QE system is adopted to study and analyzing photodiode in blood oxygen sensor including 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 contact Enlitech immediately.
Application 3: Photodiode-gated Transistor for High Gain Sensing and Imaging
In optical sensing and imaging applications, in order to improve sensitivity and SNR, APS (active pixel sensor) includes a photodetector or a photodiode and several transistors to form a multi-component circuit. One of the important units: the in-pixel amplifier, also known as the source follower, must be used. Since its birth, APS has evolved from a three-transistor circuit to a five-transistor circuit to solve issues such as blooming and reset noise. In addition to APS, avalanche photodiodes (APD) and related products: silicon photomultipliers (SiPM) can also obtain high sensitivity. However, since a high electric field must be used to initiate photomultiplication and impact ionization, the shot noise caused by the high field is very serious in these devices.
Recently, the concept of a sub-threshold operating photodiode (PD) gated transistor device has been proposed. It can achieve high gain without high field or multi-transistor circuits. The gain is derived from the light-induced gate modulation effect, in order to achieve this, sub-threshold operation must be performed. 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, making it 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 (ΔVth) 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) Schematic structure of a-Si:H photodiode-gated LTPS TFT;
(b) Equivalent circuit diagram, showing APS with high SNR.
(a) Micrograph of the pixel; (b) Micrograph of the partial array; (c) 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
This Advanced PhotoDetector can be applied to optical active pixel sensors with “indirect conversion X-ray imaging”, “optical fingerprint imaging” and “biomedical fluorescence imaging.”
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 the key to 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, in order 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 it uses 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 different 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)
An 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 = − 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.
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