清洗工艺对锗外延片表面点状缺陷的影响

锗外延片表面的雾、水印及点状缺陷等会影响太阳电池的性能和成品率,其中点状缺陷出现的比例最高。研究了锗抛光片清洗工艺对外延片表面点状缺陷的影响,获得了无点状缺陷、低粗糙度及高表面质量的锗单晶片。采用厚度为175μm p型<100>锗单面抛光片进行清洗试验,研究了SC-1溶液的不同清洗时间、清洗温度和去离子水冲洗温度对锗抛光片外延后点状缺陷的影响,分析了表面SiO_2残留和锗片表面粗糙度对外延片表面点状缺陷的影响。结果表明点状缺陷主要是由于锗单晶抛光片表面沾污没有彻底清洗干净以及清洗过程中产生新的缺陷造成的。采用氢氟酸溶液浸泡、SC-1溶液低温短时间清洗结合低温去离子水冲洗后的锗抛光片进行外延,用其制备的太阳电池光电转换效率由原来的25%提高到31%。

Effect of Cleaning Process on Point Defects on the Surface of Germanium Epitaxial Wafers

The haze, watermarks and point defects on the surface of germanium epitaxial wafers will affect the performance and yield of solar cells, among which the proportion of point defects is the highest. The effect of cleaning process of Ge polished wafer on the point defects on the surface of the epitaxial wafer was studied. The Ge single crystal wafer with no point defects, low roughness and high surface quality was obtained. A p-type <100> Ge single side polished wafer with a thickness of 175 μm was used for cleaning experiment. The effects of different cleaning time and temperature of SC-1 solution, deionized water washing temperature on the point defects of the Ge epitaxial wafer after polishing were studied respectively. The effects of residual SiO2 on the surface and the roughness of the Ge wafer surface on the point defects of the epitaxial wafer were analyzed. It is showed that the point defects are mainly caused by the new defects induced by the cleaning process and the facts that the surface contamination on the Ge polishing wafer is not thoroughly cleaned. The Ge polished wafer was used for epitaxy after soaking in HF solution, cleaning in SC-1 solution at low temperature for short time and rinsing in low temperature deionized water. The photoelectric conversion efficiency of the solar cells prepared by the Ge epitaxial wafer increase from 25% to 31%.