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Publication Date
May 31, 2017
Knowledge Repository of SEMI,CAS
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<div>With the development of semiconductor technology, chip integration and information processing technology including the big data, transmission technology of voluminous data becomes more and more important. Photonics technology with low power cost, high bandwidth, low noise and anti-electromagnetic interference is receiving attention from the industrial circle. The optical interconnection technology is considered to be one of the best solutions to break through the bottleneck of electrical interconnection, with advantage over classic electrical interconnection on low signal delay, power cost and high bandwidth, and is taken used in high-performance computing and data center. what's more, the development in information industry in the 21st century especially in new technology like internet, cloud computing and internet of things makes extreme requests on communication technology, including higher communication bandwidth, higher stability, higher user cover rate and lower cost in money, which pave the way to higher level application platform for optical interconnection.</div><div>The most popular Photonics technology in use is the InP base devices and chips. But because of the high price in material and process technology, the InP base device is not suitable for large scaled application. Compared with the InP base device, the Si base device with lower cost and higher stability is given attention from researchers. As a result, Si photonics based on CMOS process is quickly developed in recent 10 years, and is payed attention to by big international companies including Intel, IBM, Luxtera, Kotura, Compass-EOS and Huawei.</div><div>As one of the key assembly unit in the passive optical network, detectors need improvements on bandwidth and sensitivity, and the requirement is rising with the development of the industry. With inner high gain of signal, the avalanche photodiodes can improve the coverage rate and reduce the bit error rate in the optical communication networks. The development of FTTx (fiber to the x: home, building, ...), the requirement on the avalanche photodiodes is improving. In the recent development of optical network, the 4×10Gbits/s scheme is popularized and the next of 4×25Gbits/s scheme of PIN-PD is paving its way for practical application. And the 25Gbits/s Ge/Si APD device packing is exhibited by the SiFotonics Inc. in 2016. High speed Ge/Si APD still needs improvement in performance. What's more, Ge/Si APD is promising in low light level near infrared detection.</div><div>This thesis focused on the research of Ge/Si APD, studied the tunneling APD with high frequency response and big gain-bandwidth product, the lateral APD with special mechanism of high field confinement and high gain by using theoretical simulation. And we prepared the Ge/Si separate absorption charge and multiplication APD.</div><div>The main results and conclusions are described as follows:</div><div>(1)<span style="white-space: pre" class="Apple-tab-span"> </span>To solve the Gain-bandwidth product restriction of SACM APD when the avalanche gain is high, we come up with a Ge/Si APD with an ultra-thin barrier layer, and improve the high frequency response and gain-bandwidth product by bringing in the high frequency tunneling effect. When the barrier layer thickness was 2nm and bandgap of the barrier layer is 4.5eV, the tunneling APD reached the maximum value of the GBP of 286GHz. Compared with the structure without barrier layer with GBP value of 242GHz, the optimized tunneling APD improved the GBP with 18%.</div><div>(2)<span style="white-space: pre" class="Apple-tab-span"> </span>To improve the avalanche gain of SACM APD restricted by space charge effect, we design a lateral APD structure. Through theoretical research and simulation analysis, we find special electric separation mechanism of the structure. And the optimized lateral APD structure with 0.3μm-thick Si mesa and substrate Si impurity concentration of 2×1016cm-3 can reach high gain of 246 under -22.2dBm 1.55μm incident light,3.5 times of the SACM APD with same size of multiplication and absorption region, with high electric field confinement from the Ge/Si hetero-structure interface.</div><div>(3)<span style="white-space: pre" class="Apple-tab-span"> </span>By controlling the material property, impurity distribution and optimizing the semiconductor device fabrication process, we designed and prepared the test device of the Ge/Si SACM APD structure. The properties of I-V curve at room temperature and variable temperature from 150K to 270K is tested. The dark current at -1V of the SACM APD with a diameter of 30μm and 50μm is 0.492nA and 1.42nA, the current density is 69.6μA/cm2 and 72.3μm/cm2 respectively. The device has good avalanche effect under different incident light power. The changing rate of breakdown voltage with temperature is 10mV/K, showing good heat stability of the device.</div><div><br /></div>

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