Preparation Of Porous Silicon And Study On Its Thermoelectric Properties

The research of Si based materials that as a new type of thermoelectric materials have been attracted broad attention by researchers in recent years. It is efficiency to solve the problem of energy shortage, and of great significance to develop high performance green environmental material, and also will has a broad application prospect if the Si based thermoelectric materials that with high conversion of thermal energy and electric energy can be prepared successfully. The thermoelectric performance will be better that having higher porosity and more ordering nano-pore. Because it can be result in intense phonon scattering that carrying lots of heat then lead to the reducing of thermal conductivity of crystal lattice and at the same time having little effect to the transport of charge carrier, so it’s thermoelectric performance will be improved. Based on this, we used Si O2 nanospheres as the monolayer patternplate to prepare porous silicon(PS) that ordering and having high porosity in order to reduce the thermal conductivity effectively. Furthermore, we also adopted the double groove electrochemical corrosion method for the preparation of orderly PS with deep hole depth, which reduced the influence of bulk silicon, and we also injected Nb to the pore of PS that we found the thermal conductivity become more lower and as well as it’s resistivity, this is beneficial to the increase of ZT. The concrete content and results of our experiment are as follows:(1) Firstly, we prepared the monodisperse Si O2 nanospheres that using the improved St?ber method, in order to obtain ordered monolayer patternplate by using vertical sedimentary self-assembly method. Then we etched it after annealing. And through the contrast experiment we found out the suitable condition of the preparation.(2) The silicon that covered Si O2 nanospheres patternplate was etched through electrodeless chemical etching method. The obtained samples with relatively homogeneous and ordered pores, and the corrosion rate is faster and porosity is higher than that without covered Si O2 patternplate. The property of thermal conductivity was measured and analysised.(3) In order to increase the depth of PS that avoiding bulk silicon effect, we adopted the electrochemical corrosion method. By using the patternplate, the corrosion rate is faster and porosity is higher.(4) The testing for prepared samples indicate that the thermal conductivity is obviously decreased compared with bulk silicon. The pore depth is about 224μm, and the conductivity is 29W/K×m at 300 K which sample of etching 90 min by using the patternplate. Furthermore, it is further reduce to 15 W/K×m at 300 K after be injected Nb that is significantly low compared to bulk silicon. At the same time as the large surface roughness, high porosity and the structure with nanopore which lead to thermal conductivity decreased of the porous silicon, it is beneficial to increase its ZT, so its thermoelectric properties could be improved.