退火对单层二硫化钼荧光特性的影响

单层二硫化钼是继石墨烯后的一种新型二维材料. 它是一种直接带隙半导体, 具有优异的光电特性, 从而受到人们的广泛关注. 之前的研究报道过单层二硫化钼在氩气中退火后可以提升其A激子峰的荧光强度, 但我们发现, 空气中退火较氩气退火效果更为明显. 本文重点研究了在空气中退火对二硫化钼的荧光特性的影响. 不同条件下制备的单层二硫化钼样品, 经过在空气中退火处理后, 荧光峰位均发生了蓝移, 荧光强度提升了一个数量级. 我们认为, 这是由于空气退火造成二硫化钼缺陷的形成, 大量氧气分子被缺陷束缚并发生电荷转移. 氧气分子充当受主的角色, 起着P型掺杂的作用. 电荷的抽取造成二硫化钼的负电激子减少, 中性激子增多, 提升了其荧光量子效率. 我们在对照实验中发现, NH₃吸附在二硫化钼表面时, 荧光强度下降, 峰位红移, 这是由于NH₃分子充当施主的角色, 造成负电激子增多, 中性激子减少. 本文为提高单层二硫化钼的荧光量子效率提供了一种简单有效的方法.     

Influence of Fe Contamination on the Minority Carrier Lifetime of Multi-crystalline Silicon

We investigate the influence of Fe contamination on the minority carrier lifetimes of multi-crystalline silicon. The minority carrier lifetime is measured by the microwave photoconductive decay method. The original bulk lifetime is about 30μs after passivation with iodine solution. After intentional Fe contamination, the bulk lifetime declines with increasing temperature. Fast cooling in air conduces to the formation of more interstitial Fe （[Fe]i）. Slow cooling through the control of the furnace temperature limits the formation of more [Fe]i, but leads to the formation of precipitation. The data support the idea that the minority carrier lifetime in multi-crystalline silicon mainly depends on the distribution of Fe but not the total amount. A favorite effect of [Fe]i gettering is discovered after conventional phosphorus diffusion, and the [Fe]i concentration remaining in the silicon wafer is acceptable for solar cell applications.