HgCdTe has been shown to be the first semiconductor exhibiting single-carrier multiplication in short-wavelength, medium-wavelength, long-wavelength avalanche photodiodes detectors for cut-off wavelengths from 1.3 µm to 11 µm corresponding to compositions xcd from 0.7 to 0.2, which has the remarkable characteristics of high gain, high bandwidth and almost no excess noise. These results have opened a new horizon in photon starved and high-speed applications, such as active imaging and free space optical communications. In this paper, we report the latest results at SITP of HgCdTe eFAPDs using LPE-grown absorption layers in the SW and MW wavelength bands. The gain of single element short-wavelength HgCdTe APD for 2.57 μm cut-off wavelength is about 100 at 25V reverse bias, and GNDCD is about 1.47×10- 7A/cm2 at gain of 100 at 130K. For MW HgCdTe APDs, increase the P region doping concentration will reduce the overall dark current density and eliminate sudden rise of dark current at large bias and high temperature, and lower Cd composition could be a trade-off way for GNDCD suppression. 50 μm pitch 128×128 array HgCdTe APDs for cut-off wavelengths 4.88 µm corresponding to compositions xcd 0.307 were fabricated, whose GNDCD is less than 1×10-7A/cm2 at 8V reverse bias, gain is over 1000 at 11V reverse bias. A 50 μm pitch 128×128 array HgCdTe APDs with xcd=0.29 was manufactured, whose gain reaches 1570 at 9.8V reverse bias, the average excess noise factor is 1.25 at average gain of 133, noise equivalent photon is about 12 at average gain of 113. By thinning the absorption region thickness, the response bandwidth of Hg0.79Cd0.31Te APD reaches 635MHz under 1V reverse bias. Moreover, the medium-wavelength focal plane of 320×256 array is demonstrated the imaging, and the low noise, high sensitivity and fast imaging characteristics of HgCdTe APDs under linear avalanche gain are verified.
HgCdTe electron avalanche photodiodes (e-APDs) with single-carrier multiplication hold great promise for weak signal detection. This work investigates the key metrics that affect the signal-to-noise ratio of mid-wavelength infrared (MWIR) Hg0.7Cd0.3Te e-APD: current, gain, and excess noise factor. The gain is over 1000 at -10 V, but the maximum useful gain is limited by the generation of band-to-band tunneling current at higher bias voltages. The gain dispersion obtained by characterizing the focal plane array is 4.7% at -7 V, indicating a relatively homogeneous gain from pixel to pixel. The excess noise factors evaluated by the noise power spectral density and the gain fluctuation methods both range from 1 to 1.32 at gains below 400, demonstrating the property of near excess-noise-free amplification of HgCdTe e-APDs.
HgCdTe has been shown to be the first semiconductor exhibiting single-carrier multiplication in avalanche photodiodes (APDs) up to gain values larger than 1000 and with close to zero excess noise. These results have opened a new windows for low-flux and versatile imaging. In this paper, we report the latest results on a 50μm pitch 128×128 array HgCdTe APDs with xcd=0.307 manufactured at SITP. Through optimizing the implantation parameters and annihilation parameters, the designed PIN junction structure could be obtained, and then the performance of APD device was improved. The APDs display a gain of 728 around 10V reverse bias, and the standard deviation of the gain was 18.3% of the mean gain of 113 at 7.8V. The GNDC is less than 100nA/cm2 at the bias<9V, but the dark current starts increasing significantly faster than the gain at high bias, and then the device becomes dark current noise limited. The excess noise factor F is less than 1.8 up to gain of 700, and the F factor of 94.75% pixels is less than 1.4 at gain of 126. The Noise Equivalent Photon (NEPh) is 16 photons at gain of 500, and a demonstration imaging was shown.
The HgCdTe avalanche photodiode (APD) with built-in gain mechanism has great application prospects in the field of weak light signal detection. Any dark current will be converted into noise affecting the work efficiency of photodetectors. Therefore, the study of dark current mechanism is an important way to obtain high performance HgCdTe APD. In this paper, the photoelectric detection mechanism of planar junction electron injection HgCdTe APD is systematically studied, focusing on two aspects of structural optimization design and performance improvement. The dependence of device performance parameters on structure parameters is obtained by comparing the simulation results and experimental results. The lower the trap concentration, the smaller the dark current under small reverse bias voltage is, and the higher the operation voltage is. The dark current density of HgCdTe APD array is about 10-8 A/cm2 under small bias voltage. In addition to the material parameters, the dark current is mainly related to the internal electric field, which is affected by the width and doping concentration of the depletion region. The results show that device structure is the major determinant for the performance difference of HgCdTe APD. The structural optimization direction of high-performance HgCdTe APD is to further suppress the local electric field and reduce the dark current by adjusting the process.
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