Li Yijie, Toan Nguyen Van, Wang Zhuqing, Samat Khairul Fadzli, Ono Takahito
Department of Mechanical Systems Engineering, Tohoku University, Aoba-ku Sendai 980-8579, Japan.
Nanotechnology. 2020 Nov 6;31(45):455705. doi: 10.1088/1361-6528/ab8fe1. Epub 2020 May 4.
A silicon substrate consisting of nanoporous silicon film could enhance the thermoelectric performance of bulk silicon due to its low thermal conductivity. Metal-assisted chemical etching (MACE) is a wet method for fabricating diverse nano/micro structures, which uses a noble metal as the catalyst for etching of semiconductor materials. In this study, we report the thermoelectrical properties of silicon substrates with nanopores in different porosities fabricated by MACE employing Ag nanoparticle as a metal catalyst. Different porosities of the nanoporous silicon layer were obtained by adjusting the deposition time of Ag nanoparticles. The lateral nanopores were found on the surface of the vertical nanopores sidewall caused by Ag nanoparticles. With the increase of the porosity, the surface area of the nanopores sidewall became rougher. In comparison with single-crystal silicon, silicon substrates with nanopores can enhance the thermoelectric figure of merit, ZT, due to the relativity high Seebeck coefficient and low thermal conductivity. However, lower electrical conductivity limits the enhancement of the ZT value. The porosity effect on the thermoelectrical properties of silicon substrates with nanopores was evaluated. The Seebeck coefficient has a maximum value at a porosity of 38% and then decreases at a porosity of 49%, and the electrical conductivity and thermal conductivity decrease with the increase of porosity. At a porosity of 38%, the ZT value of silicon substrates with nanopores can reach approximately 0.02, which is 7.3 times larger than that of the original high-doped single-crystalline silicon. Thus the nanoporous silicon film fabricated by MACE can enhance the thermoelectric performance of the bulk silicon.
由纳米多孔硅膜构成的硅衬底因其低导热率可提高体硅的热电性能。金属辅助化学蚀刻（MACE）是一种用于制造各种纳米/微结构的湿法，它使用贵金属作为蚀刻半导体材料的催化剂。在本研究中，我们报告了采用银纳米颗粒作为金属催化剂通过MACE制备的具有不同孔隙率的纳米孔硅衬底的热电性能。通过调整银纳米颗粒的沉积时间获得了不同孔隙率的纳米多孔硅层。在由银纳米颗粒引起的垂直纳米孔侧壁表面发现了横向纳米孔。随着孔隙率的增加，纳米孔侧壁的表面积变得更粗糙。与单晶硅相比，具有纳米孔的硅衬底由于相对较高的塞贝克系数和低导热率，可以提高热电优值ZT。然而，较低的电导率限制了ZT值的提高。评估了孔隙率对具有纳米孔的硅衬底热电性能的影响。塞贝克系数在孔隙率为38%时具有最大值，然后在孔隙率为49%时下降，并且电导率和导热率随着孔隙率的增加而降低。在孔隙率为38%时，具有纳米孔的硅衬底的ZT值可达到约0.02，这比原始的高掺杂单晶硅大7.3倍。因此，通过MACE制备的纳米多孔硅膜可以提高体硅的热电性能。
