Introduction, photon counting type linear avalanche photodetector
Photon counting technology can fully amplify the photon signal to overcome the readout noise of electronic devices, and record the number of photons output by the detector in a certain period of time by using the natural discrete characteristics of the detector output electrical signal under weak light irradiation, and calculate the information of the measured target according to the value of the photon meter. In order to realize extremely weak light detection, many different kinds of instruments with photon detection capability have been studied in various countries. A solid state avalanche photodiode (APD photodetector) is a device that uses the internal photoelectric effect todetect light signals. Compared with vacuum devices, solid-state devices have obvious advantages in response speed, dark count, power consumption, volume and magnetic field sensitivity, etc. Scientists have carried out research based on solid-state APD photon counting imaging technology.
APD photodetector device has Geiger mode (GM) and linear mode (LM) two working modes, the current APD photon counting imaging technology mainly uses Geiger mode APD device. Geiger mode APD devices have high sensitivity at the level of single photon and high response speed of tens of nanoseconds to obtain high time accuracy. However, Geiger mode APD has some problems such as detector dead time, low detection efficiency, large optical crossword and low spatial resolution, so it is difficult to optimize the contradiction between high detection rate and low false alarm rate. Photon counters based on near-noiseless high-gain HgCdTe APD devices operate in linear mode, have no dead time and crosstalk restrictions, have no post-pulse associated with Geiger mode, do not require quench circuits, have ultra-high dynamic range, wide and tunable spectral response range, and can be independently optimized for detection efficiency and false count rate. It opens up a new application field of infrared photon counting imaging, is an important development direction of photon counting devices, and has broad application prospects in astronomical observation, free space communication, active and passive imaging, fringe tracking and so on.
Principle of photon counting in HgCdTe APD devices
APD photodetector devices based on HgCdTe materials can cover a wide range of wavelengths, and the ionization coefficients of electrons and holes are very different (see Figure 1 (a)). They exhibit a single carrier multiplication mechanism within the cut-off wavelength of 1.3~11 µm. There is almost no excess noise (compared with the excess noise factor FSi~2-3 of Si APD devices and FIII-V~4-5 of III-V family devices (see Figure 1 (b)), so that the signal-to-noise ratio of the devices almost does not decline with the increase of gain, which is an ideal infrared avalanche photodetector.
FIG. 1 (a) Relationship between the impact ionization coefficient ratio of mercury cadmium telluride material and component x of Cd; (b) Comparison of excess noise factor F of APD devices with different material systems
Photon counting technology is a new technology that can digitally extract optical signals from thermal noise by resolving the photoelectron pulses generated by a photodetector after receiving a single photon. Since the low-light signal is more dispersed in the time domain, the electrical signal output by the detector is also natural and discrete. According to this characteristic of weak light, pulse amplification, pulse discrimination and digital counting techniques are usually used to detect extremely weak light. Modern photon counting technology has many advantages, such as high signal-to-noise ratio, high discrimination, high measurement accuracy, good anti-drift, good time stability, and can output data to the computer in the form of digital signal for subsequent analysis and processing, which is unmatched by other detection methods. At present, the photon counting system has been widely used in the field of industrial measurement and low-light detection, such as nonlinear optics, molecular biology, ultra-high resolution spectroscopy, astronomical photometry, atmospheric pollution measurement, etc., which are related to the acquisition and detection of weak light signals. The mercury cadmium telluride avalanche photodetector has almost no excess noise, as the gain increases, the signal-to-noise ratio does not decay, and there is no dead time and post-pulse restriction related to Geiger avalanche devices, which is very suitable for application in photon counting, and is an important development direction of photon counting devices in the future.
Post time: Jan-14-2025