A photodiode is a semiconductor device that converts light into current, with an intrinsic layer between the p (positive) and n (negative) layers. A photodiode accepts light energy as input to generate current. Photodiodes are also known as photodetectors, photosensors, or light detectors, and commonly include photodiodes (PIN), avalanche photodiodes (APD), single photon avalanche diodes (SPAD), and silicon photomultiplier tubes (SiPM/MPPC).
Figure: Classification of detectors
Photodiode (PIN)Also known as PIN junction diode, in the photodiode PN junction doped into the middle of a layer of very low concentration of type I semiconductor, you can increase the width of the depletion zone to reduce the impact of diffusion movement, improve the response speed of the purpose. Because of this doped layer of low doping concentration, nearly intrinsic (Intrinsic) semiconductor, so called l layer, so this structure becomes PIN photodiode.
Avalanche Photodiodes (APD)It is a photodiode with internal gain, similar in principle to a photomultiplier tube. After adding a high reverse bias voltage (generally 100-200V in silicon), an internal current gain of about 100 can be obtained in the APD by using the ionization collision (avalanche breakdown) effect.
Single Photon Avalanche Diode (SPAD)It is a photodetectable avalanche diode with single-photon detection capability, working in Geiger mode APD (Avalanche Photon Diode). It is used in Raman spectroscopy, positron emission tomography and fluorescence lifetime imaging.
Silicon Photomultiplier (SiPM)It is an avalanche photodiode array composed of avalanche breakdown voltage and avalanche burst mechanism in parallel, with good photon number resolution and single-photon detection sensitivity of the silicon-based weak light detector, with high gain, high sensitivity, low bias voltage, insensitive to magnetic field, compact structure and so on.
PIN photodiodes do not have a multiplier effect and are often used in short-range detection, while APD avalanche photodiodes are more mature and are the most widely used photodetector. Currently, the typical gain of APD is 10-100 times, and it is necessary to significantly increase the light intensity of the light source in order to ensure that the APD has a signal in long-distance testing. SPAD single-photon avalanche diodes and SiPM/MPPC silicon photomultiplier tubes mainly exist to solve the problem of gain capability and the realization of large-size arrays.
1) SPAD or SiPM/MPPC are APDs working in Geiger mode, which can obtain tens to thousands of times gain, but the system cost and circuit cost are higher.
2) SiPM / MPPC is an array of multiple SPAD form, through multiple SPAD to obtain a higher range of detectability and with the use of array light source, easier to integrate CMOS technology, with the cost advantages of large-scale mass production. In addition, due to the SiPM operating voltage is mostly lower than 30V, do not need high-voltage system, easy to integrate with mainstream electronic systems, the internal gain also makes the SiPM on the back-end readout circuit requirements are simpler. At present, SiPM is widely used in medical instruments, laser detection and measurement (LiDAR), precision analysis, radiation monitoring, security detection and other fields, with the continuous development of SiPM will be expanded to more areas.
Table: Comparison of SiPM/MPPC, SPAD, APD, PIN-PD detector parameters
Photodetector photoelectric test
Photodetectors generally need to first test the wafer, packaging and then the device for the second test, to complete the final characterization and sorting operations; photodetectors in the work, the need to apply reverse bias voltage to pull open the light injected into the resulting electron-hole pairs, so as to complete the process of photogenerated carriers, photodetectors are usually working in the reverse state; test is more concerned about the dark current, reverse breakdown voltage, Junction capacitance, responsivity, crosstalk and other parameters.
Photodetector photoelectric performance characterization using digital source meters
One of the best tools for the characterization of optoelectronic performance parameters is the digital source meter (SMU). As an independent voltage or current source, the SMU can output constant voltage, constant current, or pulse signals, and can also be used as a meter for voltage or current measurements; it supports Trig triggering, which can realize the linkage of multiple meters; and for single-sample testing of photodetectors as well as multi-sample validation testing, the SMU can be used to build a complete test program directly from a single SMU, multiple SMUs, or plug-in SMUs.
Purcells Digital Source Meter Builds Photodetector Photoelectric Test Solution
dark current
Dark current is the PIN / APD tube in the absence of light, increase a certain inverse bias current; its nature is generated by the structural properties of the PIN / APD itself, and its size is usually below uA level. When testing, we recommend the use of Purcell S series or P series source meter, S series source meter minimum current 100pA, P series source meter minimum current 10pA.
Reverse breakdown voltage
When the applied reverse voltage exceeds a certain value, the reverse current will suddenly increase, and this phenomenon is called electrical breakdown. The critical voltage that causes electrical breakdown is called the diode reverse breakdown voltage. According to the specifications of the device is different, its withstand voltage index is not consistent, test the instrumentation required is also different, the breakdown voltage in the 300V below the recommended use of S-series desktop source meter or P-series pulse source meter, the maximum voltage of 300v, breakdown voltage in the 300V above the device is recommended to use the E-series, the maximum voltage of 3500V.
C-V Testing
Junction capacitance is an important property of the photodiode, the photodiode bandwidth and response has a great impact. Photoelectric sensors need to note that the larger the PN junction area of the diode junction volume is also larger, also has a larger charging capacitance. In reverse bias applications, the width of the depletion region of the junction increases, which will effectively reduce the junction capacitance and increase the response speed; photodiode C-V test program consists of the S series source meter, LCR, test fixture box, and the host computer software.
responsiveness
The responsivity of a photodiode is defined as the ratio of the generated photocurrent (IP) to the incident optical power (Pin) at a specified wavelength and reverse bias, and is usually expressed in units of A/W. The responsivity is related to the magnitude of quantum efficiency, and is the extrinsic manifestation of quantum efficiency, and is recommended to be tested with a Purchase S-series or a P-series source meter, with the S-series source meter having a minimum current of 100 pA, and the P-series source meter having a minimum current of 10 pA. The minimum current of S series source meter is 100pA, and the minimum current of P series source meter is 10pA.
Optical crosstalk test (Crosstalk)
In the field of LIDAR, the number of photodetectors used in LIDAR products with different line counts is different, and the spacing between the photodetectors is also very small, so there will be mutual optical crosstalk when multiple photoreceptors are working at the same time during the process of using, and the existence of optical crosstalk will seriously affect the performance of LIDAR.
Optical crosstalk in two forms: a photodetector in the array above the larger angle of incident light in the photodetector is completely absorbed by the photodetector before entering the neighboring photodetector and is absorbed; the second is a large angle of incident light is not part of the incident light into the sensing area, but is incident to the photodetector between the interconnecting layer and reflected into the sensing area of the neighboring device.
Figure: Schematic diagram of crosstalk generation mechanism
Array detector optical crosstalk test is mainly for array DC crosstalk test, refers to the reverse bias, wavelength and optical power under the provisions of the array diode in the photocurrent of the light unit and any one of the neighboring units of photocurrent ratio of the maximum value. The test is recommended to use the Purcell S series, P series or CS series of multi-channel test program.
S/P Series Source Meter Test Program
CS Series Multi-Channel Test Solutions
The solution mainly consists of CS1003c/ cS1010C mainframe and CS100/CS400 daughter card, featuring high channel density, strong synchronous triggering function and high efficiency of multi-device combination.
CS1003C/CS1010C: customized frame, backplane bus bandwidth up to 3Gbps, support 16-way trigger bus, to meet the needs of multi-card device high-speed communication, CS1003C has a maximum of 3 daughter card slots, CS1010C has a maximum of 10 daughter card slots.
CS100 daughter card: a single card, single-channel daughter card, with four-quadrant capability, maximum voltage of 300v, minimum current of 100pA, output accuracy of 0.1%, the maximum power of 30W; with the CS1010 host can build up to 10 test channels.
CS400 daughter card: a single card four-channel word card, the card 4-channel common ground, the maximum voltage 10V, maximum current 200mA, the output accuracy of 0.1%, the maximum power of a single channel 2W; with the CS1010 host can build up to 40 test channels.
Optocoupler (OC) electrical performance test program
Optical coupler (optical coupler, abbreviated as OC), also known as optical isolator or photocoupler, referred to as optocoupler. It is a light-mediated transmission of electrical signals to the device, generally consists of three parts: light emission, light reception and signal amplification. Input electrical signals to drive light-emitting diodes (LEDs), so that it emits a certain wavelength of light, received by the photodetector and produce photocurrent, and then further amplified output. This completes the conversion of electricity and light - electricity, thus playing the role of input, output, isolation.
As the optocoupler input and output are isolated from each other, the electrical signal transmission has a unidirectional nature and other characteristics, and thus has a good electrical insulation and anti-jamming ability, so it has been widely used in a variety of circuits. At present it has become one of the most varied and widely used optoelectronic devices.
For optocoupler devices, its main electrical performance characterization parameters are: forward voltage VF, reverse current lR, input capacitance CIN, emitter-collector breakdown voltage BVcEo, current conversion ratio CTR and so on.
Forward voltage VF
VF is the voltage drop across the LED itself at a given operating current. Common low-power LEDs are usually tested with mA current to test the forward operating voltage. It is recommended to use Prosser S series or P series source meter for testing.
Reverse leakage current lR
Usually refers to the reverse current flowing through the photodiode at the maximum reverse voltage, usually the reverse leakage current is at the nA level. It is recommended to use Prosser's S or P series source meters for testing, as the source meters have the ability to operate in four quadrants and can output negative voltages without the need for adjustment circuits. When measuring low level currents (<1uA), triple coaxial connectors and triple coaxial cables are recommended.
Emitter-collector breakdown voltage BVCEO
It is the V when the output current starts to increase dramatically during the process of increasing the voltage of the collector-emitter stage under the condition of open circuit at the input.CEOValue.
According to the different specifications of the device, its withstand voltage index is not consistent, test the instrumentation required is also different, breakdown voltage in the following 300V recommended use of the S series of desktop source table or P series of pulse source table, the maximum voltage of 300V, breakdown voltage in the 300V above the device is recommended to use the E series, the maximum voltage of 3500V.
Current Transition Ratio CTR
Current transfer ratio CTR (Current Transfer Radio), the output voltage of the output tube for the specified value, the output current and light-emitting diode forward current ratio for the current transfer ratio CTR. test recommended use of the Purcell S series or P series source meter.
Isolated Voltage
The value of the insulation voltage between the input and output of the optocoupler. Usually the isolation voltage is high and requires large voltage equipment for testing, we recommend the E series source meter with a maximum voltage of 3500V.
Isolation capacitance Cf
Isolation capacitance Cr refers to the capacitance value between the input and output of an optically coupled device. The test program consists of an S series source meter, a digital bridge, a test fixture box, and an upper computer software.
summarize
Wuhan Purcells has been focusing on the development of semiconductor electrical test instruments, based on the core algorithms and system integration and other technology platform advantages, the first independent research and development of high-precision digital source meter, pulse source meter, narrow pulse source meter, integrated plug-in source meter and other products, widely used in the field of semiconductor device and material analysis and testing. We are able to match the most efficient and cost-effective semiconductor test program according to the user's needs.
For more information about the system construction program and test line connection guide, welcome to call us!
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