Design and Characteristics of Guardring-Free Planar AlInAs Avalanche Photodiodes

This paper reports a guardring-free planar AlInAs avalanche photodiode (APD) for optical fiber communications. AlInAs APDs can achieve a larger gain-bandwidth product (GBP) with lower excess noise than commercial InP APDs, and the guardring-free planar structure enables these superior AlInAs APDs to have both a low dark current and high reliability for practical use. We present the structure, fabrication, designs, APD characteristics, and receiver sensitivity, systematically. The guardring-free planar structure and its peculiarities are described, and we show APD designs for 2.5-Gb/s and 10-Gb/s applications and their characteristics. A 0.2-mu m-thick AlInAs multiplication layer achieves a GBP of 120 GHz and an excess noise factor of 2.9 at a multiplication factor of 10. Their dark currents are less than 20 nA and their lifetime is evaluated to be 25 million hours at 85 degrees C. Lastly, we demonstrate that the guardring-free planar AlInAs APDs with a transimpedance amplifier achieve the remarkable sensitivity of -37.0 dBm at a bit error rate of 10(-10) for 2.5-Gb/s signals and of -29.9 dBm at a bit error rate of 10(-12) for 10-Gb/s signals. This performance indicates that the guardring-free planar AlInAs APDs have made great advances against commercial InP APDs and other AlInAs APDs.