采用Al/TaN叠层电极提高Si基Ge PIN光电探测器的性能

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24 μ的探测器在1.55 μ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.

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

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 Al and Al/TaN electrodes are comparatively studied.It is found that 3 dB bandwidth of photodetector with 24μm mesa diameter using an Al/TaN stack electrode is improved by four times more than that of the same structure Ge PIN photodetector using an Al electrode under—1V bias at 1.55μm.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.