High-speed waveguide Ge/Si avalanche photodiode with a gain-bandwidth product of 615 GHz

Abstract

High-sensitivity and high-bandwidth receivers are always demanded for high-speed optical link systems. As a key element, an avalanche photodiode (APD) is often regarded as one of the most attractive options for achieving high sensitivity owing to the potential high internal gain. In this paper, a 48-GHz waveguide Ge/Si avalanche photodiode operating at the O-band (1310 nm) is designed with a lateral reach-through structure and fabricated with simplified processes. The fabricated APD shows a high primary responsivity of 0.93 A/W at the unit-gain voltage of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>−</mml:mo></mml:mrow><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>4.7</mml:mn></mml:mrow><mml:mspace width="thickmathspace"/><mml:mtext>V</mml:mtext></mml:math> . It has an avalanche gain of 12.8 and a record gain-bandwidth product of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>∼</mml:mo></mml:mrow><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>615</mml:mn></mml:mrow><mml:mspace width="thickmathspace"/><mml:mtext>GHz</mml:mtext></mml:math> with an input optical power of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>−</mml:mo></mml:mrow><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>15</mml:mn></mml:mrow><mml:mspace width="thickmathspace"/><mml:mtext>dBm</mml:mtext></mml:math> when operating at a bias voltage of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>−</mml:mo></mml:mrow><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>14</mml:mn></mml:mrow><mml:mspace width="thickmathspace"/><mml:mtext>V</mml:mtext></mml:math> . The present Ge/Si APD is used successfully for high-speed data receiving, showing a sensitivity improvement about 7.6 dB for KP4-FEC operation (i.e., <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mtext>BER</mml:mtext><mml:mo>=</mml:mo><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>2.4</mml:mn></mml:mrow><mml:mo>×</mml:mo><mml:mrow class="MJX-TeXAtom-ORD"><mml:msup><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>10</mml:mn></mml:mrow><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>−</mml:mo><mml:mn>4</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math> ) with 50 Gbps non-return-to-zero (NRZ) data, compared with the case of using the reference PIN PD on the same chip. The sensitivity of the receiver with the present APD for NRZ signals is about <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>−</mml:mo></mml:mrow><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>21.3</mml:mn></mml:mrow><mml:mspace width="thickmathspace"/><mml:mtext>dBm</mml:mtext></mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>−</mml:mo></mml:mrow><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>17.8</mml:mn></mml:mrow><mml:mspace width="thickmathspace"/><mml:mtext>dBm</mml:mtext></mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>−</mml:mo></mml:mrow><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>12.6</mml:mn></mml:mrow><mml:mspace width="thickmathspace"/><mml:mtext>dBm</mml:mtext></mml:math> for KP4-FEC operation with different data rates of 50 Gbps, 80 Gbps, and 100 Gbps, while the sensitivity for four-level pulse amplitude modulation signals is about <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>−</mml:mo></mml:mrow><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>13.2</mml:mn></mml:mrow><mml:mspace width="thickmathspace"/><mml:mtext>dBm</mml:mtext></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>−</mml:mo></mml:mrow><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>11.3</mml:mn></mml:mrow><mml:mspace width="thickmathspace"/><mml:mtext>dBm</mml:mtext></mml:math> for KP4-FEC operation with different data rates of 25 and 50 Gbaud. Such high-performance APDs pave the way to achieve high-speed and high-sensitivity data transmissions.