Fabrication of Mg2Si thermal-to-electric energy conversion device using die-casting sysnthesis method

随着太阳能电池发电的普及，对转换效率更高的太阳能电池的需求越来越大。可以用于能源转换的材料必须是环境友好的半导体，即具有组成元素丰富和加工副产品无毒的优点。Sil-xGex合金被认为是产生载流子倍增(俄歇产生)的候选材料，当Ge含量约为68%时，其转换效率可达30%。Sil-xGex合金不仅是微电子器件的重要材料，而且是太阳能电池和热电器件等固态发电机的重要材料，因为它们具有化学稳定性和高温机械强度，并且在热学和电学特性方面与n-/p-型合金非常匹配，使器件能够更好地运行。然而，由于Si-Ge系统显示出复杂的…传统的Bridgman法、Czochralski法和浮区法在较多的固溶体中选择性地析出具有一定组成的硅或锗的晶体是不容易的。到目前为止，我们已经用改进的Bridgman技术结合压铸法生长了Sil-xGex大块晶体，但还没有实现对其成分均匀性和厚度的精确和可重复性的控制。为了实现任意组份的Sil-xGex晶片，我们发展了一种新的制备方法--晶片贴近法。该方法可制备出x=0.3~0.7的块体多晶Sil-xGex，成分均匀度略有偏差0.5%。所生长的Sil-xGex晶体为15×15 mm~2，厚度为3 mm。晶片接近法允许通过简单地改变生长温度和持续时间来控制晶片厚度和成分x。用光学显微镜分析了样品的微观结构，用电子探针分析了样品的成分。对生长的样品进行了室温光电导测试。用太阳模拟器测量了磷硅酸盐玻璃(PSG)磷掺杂具有pn结的样品的室温I-V特性。研究结果表明，新开发的晶片邻近生长技术能够以可重复的方式制备用于俄歇产生的块体Sl-xGex(x~0.6-0.7)晶体。较少

With the spread of solar-cell power generation, the demand for solar cells with higher conversion efficiency is increasing. It is necessary that the materials which can be used for energy-conversion applications should be environmentally-benign semiconductors, namely, they possess the advantages of abundance of their constituent elements and non-toxicity of their processing by-products. Sil-xGex alloys is known as a candidate material for producing carrier multiplication (Auger generation), which allows a conversion efficiency of 30% when the Ge amount is about 68%. Sil-xGex alloys are important materials not only for microelectronic devices but also for solid-state power generators such as solar cells and thermoelectric devices, because of their chemical stability, mechanical strength at elevated temperatures, and a close match of the n-/p-type alloys in terms of their thermal and electrical characteristics enable better device operation. However, since the Si-Ge system shows a comple … More te series of solid solutions with a phase relationship, it is not easy to precipitate crystals possessing a certain composition of silicon or germanium selectively by using conventional Bridgman, Czochralski and floating-zone methods.So far, we have performed bulk crystals growth of Sil-xGex using an advanced version of the Bridgman technique combined with a die-casting growth method, but precise and reproducible control of their compositional uniformity and thickness were not accomplished. In order to realize Sil-xGex wafer with an arbitrary composition, we have developed a new method of preparing Sil-xGex by a wafer-proximity method. This method enables to form bulk polycrystalline Sil-xGex with x=0.3~0.7, with slight deviation of ?}0.5% for the compositional uniformity. The grown Sil-xGex crystals obtained were 15x15 mm2 and 3 mm thick. The wafer-proximity method allows the control of the wafer thickness and composition x by simply changing the growth temperature and the duration. The microstructure of the samples was analyzed by using an optical microscope, and their composition was determined by electron-probe microanalysis. For the grown specimens room temperature photoconductivity measurement was carried out. The room temperature I-V characteristics of the samples, which possess pn junction by phosphorus doping using phosphor silicate glass (PSG) were measured using a solar-simulator. The obtained results imply that the newly developed wafer-proximity growth technique can fabricate bulk Sil-xGex (x~0.6-0.7) crystal for Auger generation in a reproducible manner. Less