High Speed and Low Breakdown Voltage Germanium Silicon Avalanche Photodetectors

高速與低崩潰電壓矽鍺雪崩式光偵測器

曾治國

《光學工程》 125期 (2014/06) Pp. 19-25

摘要

A novel, low breakdown voltage Ge/Si avalanche photodetector (APD) was demonstrated using a separated multiplication and absorption (SAM) device configuration, where a lateral Si avalanche pin is cascaded with a vertical Ge/Si pin for the first time. A record low breakdown voltage of -7.2 V is accomplished. Because the fabrication process is not critical and can be implemented by standard CMOS process, the device is potential to be integrated with other electronics and Si photonics and applied for high-performance optical receivers. The lateral Si avalanche pin is featured with many interdigitated pin junctions. Due to the narrow i-region (150 nm) of the pin, low breakdown voltage and high speed Si-APD was investigated. A breakdown voltage of -6.78 V and a 3-dB bandwidth of 10 GHz give significant breakthrough for Si-based APD devices. Moreover, the gain-bandwidth product is up to 276 GHz and the amplified responsivity is 1.424 A/W. To achieve monolithic integration of Ge on Si, a self-aligned microbonding technique is invented to make the Ge/Si heterojunction pin photodiode for the first time. The single-crystal Ge is developed first by rapid melt growth method on Si. Then the Ge structure is self-aligned bonded on the Si waveguide through surface tension force. The experimental result shows an on-off current ratio up to 6 orders of magnitude, a responsivity of 0.7 A/W and a 3-d B bandwidth of 17 GHz. By integrating the above Ge/Si heterjunction pin on the lateral interdigitated Si-APD, the low breakdown voltage Ge/Si SAM APD is successfully implemented A new three-terminal device structure is proposed and simulated by a professional semiconductor simulation tool and also qualitatively matched with the experimental results. A low breakdown voltage of -7.2 V was achieved for the Ge/Si SAM APD and showed a low dark current of 10 nA level before avalanche multiplication occurs. Also, an amplified gain of 40 was obtained near the avalanche breakdown. This is a world class record that a separated absorption and multiplication Ge/Si APD can operate at the voltage less than 10 V.

並列摘要

本研究使用分離增益／吸收元件的概念成功研製出一個新穎且低崩潰電壓的矽鍺雪崩式光偵測器。其中，側向的矽雪崩式光偵測器與垂直的矽鍺PIN接面是本研究的主軸，透過兩個元件並聯的連結，足以降低目前APD所遇到的操作於高電壓（＞20V）的瓶頸。因為該研究的製程條件與標準CMOS製程相容，除了在電子領域和矽光子上有潛力外，亦可以應用在高性能的光接收器。首先，側向的矽雪崩式APD具有指叉狀的設計，因為窄線寬（～150奈米）的設計，使得元件具有高速與低崩潰電壓特性，分別為10 GHz與-6.78伏特。對於矽基為主的APD有重大突破。此外，增益頻寬乘積高達276 GHz，且增益後的響應度為1.424 A/W。為了實現整合鍺於矽材料上，本研究發明了一種自我對準微接合技術，首先被應用在矽鍺PIN元件上。透過快速熱熔磊晶法（RMG）成長單晶的鍺材料於矽基板上，接著，應用表面張力來達到微小結構的接合，使得鍺成功的接合於矽光波導上。實驗結果顯示矽鍺PIN元件的on-off電流比為6個數量級，光的反應度約0.7 A/W以及17 GHz的操作頻寬，性能幾乎與商用級的磊晶元件不相上下。藉由整合矽鍺異質接面PIN在側向的矽雪崩式APD上，成功地發展出一個低崩潰電壓的矽鍺APD，透過半導體電性模擬工具來模擬此三端點的元件操作，定性上與實驗結果相當匹配。此矽鍺APD元件的低崩潰電壓和暗電流約-7.2 V與10 nA。再者，放大的增益約為40。尤其在操作電壓部份，這是一個世界級的記錄，利用分離的吸收／增益矽鍺APD概念，電壓可以操作在低於10 V，對於未來的產業應用是一大佳音。