GaAsSb/AlGaAsSb Avalanche Photodiode With High Gain-Linearity

Avalanche photodiodes (APDs) are widely used in near-infrared optical receivers to detect weak and/or high-speed optical signals. Emerging high-order optical signal modulation formats require the APD’s photocurrents to vary linearly with the signal power. There is, however, a lack of comprehensive understanding of the linearity of APD’s photocurrent and gain versus optical power characteristics underpinned by experimental results. An experimental study was carried out on the linearity of near-infrared APD’s photocurrent and avalanche gain with optical signal power, covering a wide range of optical power and APD’s operating voltage. The work utilized thin 200-nm Al<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.85</sub>Ga<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.15</sub>As<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.56</sub>Sb<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.44</sub> (AlGaAsSb) avalanche region, exploiting their excellent temperature stability compared to thick structures and other commonly used avalanche materials. Three types of linearity behaviors were identified and explained: 1) around the punchthrough voltage; 2) higher reverse bias and moderate gains; and 3) close to the breakdown voltage and large gains. The best linearity performance, tested under optical power from 0.08 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$750~\mu $ </tex-math></inline-formula> W, was achieved under high reverse bias (>18 V) but with moderate gain (<10). Our findings of linearity performance are also applicable to near-infrared APDs with other avalanche materials. Furthermore, AlGaAsSb-based APDs exhibit better linearity performance compared to a commercial non-AlGaAsSb APD. At a gain of 10, a 10% attenuation was observed at the output current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$34~\mu $ </tex-math></inline-formula> A in the commercial APD compared to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$670~\mu $ </tex-math></inline-formula> A (20 times higher) in our APD, suggesting the potential of our detector for optical communication links utilizing high-order signal modulation formats. The data reported in this article are available from the ORDA digital repository (<uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://figshare.com/s/34f0f27e42de168c5c41</uri>).