采用Al/TaN叠层电极提高Si基Ge PIN光电探测器的性能

Improvement on performance of Si-based Ge PIN photodetector with Al/TaN electrode for n-type Ge contact

金属与Ge材料接触由于存在强烈的费米钉扎效应,导致金属电极与n型Ge接触引入较大的接触电阻,限制了Si基Ge探测器响应带宽.本文报道了在SOI衬底上外延Ge单晶薄膜并制备了不同台面尺度的Ge PIN光电探测器.对比了电极分别为金属Al和Al/TaN叠层的具有相同器件结构的SOI基Ge PIN光电探测器的暗电流、响应度以及响应带宽等参数.发现在Al与Ge之间增加一薄层TaN可有效减小n型Ge的接触电阻,将台面直径为24μm的探测器在1.55μm的波长和-1 V偏压下的3 dB响应带宽提高了4倍.同时,器件暗电流减小一个数量级,而响应度提高了2倍.结果表明,采用TaN薄层制作金属与Ge接触电极,可有效钝化金属与Ge界面,减轻费米钉扎效应,降低金属与n-Ge接触的势垒高度,因而减小接触电阻和界面复合电流,提高探测器的光电性能.

Large contact resistance due to Fermi level pinning effect at the interface between metal and Ge strongly restricts the 3 dB bandwidth of Ge photodetectors. In this paper, the Ge PIN photodetectors fabricated on silicon-on-insulator substrates, respectively, with A1 and AI/TaN electrodes are comparatively studied. It is found that 3 dB bandwidth of photodetector with 24 g.m mesa diameter using an A1/TaN stack electrode is improved by four times more than that of the same structure Ge PIN photodetector using an A1 electrode under -1 V bias at 1.55 ~tm. In addition, the dark current is reduced by one order of magnitude, and optical responsivity is enhanced by two times. These results suggest that a thin metallic TaN layer as an electrode can effectively passivate the Ge surface and alleviate the Fermi-level pinning effect, thus reducing the contact resistance and the recombination current at the interface. TaN can be considered as a promising electrode material for Ge device applications.