In this study, we aim to investigate the interrelation between excess noise and bandwidth in avalanche photodiodes to explore the realization of devices with high gain-bandwidth product. Through comprehensive research and theoretical analysis, it has been determined that, regardless of the operating wavelength and temperature, HgCdTe avalanche photodiodes exhibit favorable characteristics, such as low excess noise and high bandwidth, owing to the phenomenon of single-carrier avalanche multiplication process. Consequently, they represent the optimal choice for high-performance avalanche detection.
HgCdTe avalanche photodiodes (APD) have been demonstrated to be one of the most promising paths for low flux and high speed applications. The bandwidth of HgCdTe e-APD has been theoretically predicted to be independent of the gain, owed to its strongly dominant electron multiplication. However, when the photocurrent is high, a large number of electrons exists in the depletion region, and the electrical field in the depletion region might collapse due to the space charge effect, thus limiting the increase of the gain-bandwidth product. In this work, the structure of the device was optimized by simulation, and the effect of the light injection dose on the electric field and bandwidth of the device was studied. Finally, a mid-wavelength infrared HgCdTe e-APD device whose bandwidth almost doesn't decrease with the increase of gain is fabricated. The response bandwidth of the APD is about 480MHz @ gain=625, corresponding to a gain-bandwidth product of 300GHz.
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.
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