Study Of A-Si:H Microstructure By MWECR CVD Technique

Amorphous silicon (a-Si) has the special characteristic on structure, made a-Sihas special optical and electronic characteristics , so it had huge prospect ofapplication. But there are a lot of defects (dangling band) in amorphous silicon,therefore its application have been limited. To hydrogenated amorphous silicon(a-Si:H), however, it has much less defects than non-hydrogenated a-Si, for the sakeof much hydrogen which eliminate the defects by making a bond with non-connectedSi bond. With these virtue, a-Si:H accord with device quality. The films of a-Si:Hhave widely used in solar cell field. But the deposition rate and quality of a-Si:H wasprimarily affected by preparation methods. Recently, the microwave electroncyclotron resonance (MWECR) CVD method was weightily studied. In view of itsvirtue of high degree of electron and ion generations, MWECR CVD method isexpected to deposit device quality a-Si:H at high deposition rate. Thus, we haveprepared a-Si:H films under diverse conditions using MWECR CVD. We deposit the high quality a-Si:H by MWECR CVD method in laboratory. Thedissertation mainly focuses on variation of the structure of a-Si:H as functions of thedilution ratio of H2/SiH4 and substrate temperature . At the same time, weexperimented by varying substrate temperature, and found that proper high substratetemperature is favorable to hydrogen elimination and thus improve the structure offilms. The speciality of a-Si:H films is closely associated with hydrogen content infilms. On the one hand, hydrogen incorporated as monohydride (Si-H) saturatesdangling bonds in films, and on the other hand, hydrogen incorporated as polyhydride(Si-H2,Si-H3, (Si-H2)n) introduces defect in films and thus increases the density oflocalized electronic states in band gap. The transmission spectra of films areconverted to the absorption spectra in terms of reasonable baseline. We obtainedhydrogen content and bonding configurations of films by analyzing the integratedabsorbance of the wagging mode and stretching mode. We found that hydrogencontent incorporated as monohydride maintains constant and hydrogen contentincorporated as polyhydride gradually decreases with the increase of substratetemperature. We also take a series of testing on laman spectra, which analyzing the situation in II摘 要different substrate temperature and different anneal process. As the increasing insubstrate temperature, it turn out to be a mixture state of a-Si /u-Si. At the same time,we also found optical band gap a-Si:H films decreases with the increase of substratetemperature. So, the increase of optical band gap of a-Si:H films is the result of theincrease of hydrogen content, especially incorporated as polydride.