Study Of MWECR CVD Deposition Technique For A-Si:H And Properties Of A-Si:H

Hydrogenated amorphous silicon (a-Si:H) by virtue of its superior properties is increasingly playing an important role in the high-technology field, such as film solar cells, film transistor and flat display. However, low deposition rate of a-Si:H seriously restricts its further industrializations. In order to deposit device quality a-Si:H films, various preparation methods have been thoroughly studied. In view of its virtue of high degree of electron and ion generations, the microwave electron cyclotron resonance (MWECR) CVD method is expected to deposit device quality a-Si:H at high deposition rate. Thus, we have prepared a-Si:H films under diverse conditions using MWECR CVD. Moreover, we are concerned with hydrogen content in films and discuss its effect on photoelectricity of films.Theory and practice have proved that a-Si:H films can not be prepared at high microwave power. The dissertation mainly focuses on variation of the structure of a-Si:H as functions of the dilution ratio of H2/SiH4, substrate temperature and substrate position at low microwave power. We experimented by varying the dilution ratio of H2/SiH4 at different substrate position, and found that the optimum dilution ratio of H2/SiH4 of system depends on substrate position. At the same time, we experimented by varying substrate temperature, and found that high substrate temperature is favorable to hydrogen elimination and thus improve the structure of films, but over high substrate temperature leads to the increase of dangling bonds.The photoelectric property of a-Si:H films is closely associated with hydrogen content in films. On the one hand, hydrogen incorporated as monohydride (Si-H) saturates dangling 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 of localized electronic states in band gap. The transmission spectra of films are converted to the absorption spectra in terms of reasonable baseline. We obtainedhydrogen content and bonding configurations of films by analyzing the integrated absorbance of the wagging mode and stretching mode. We found that hydrogen content incorporated as monohydride maintains constant and hydrogen content incorporated as polyhydride gradually decreases with the increase of substrate temperature. At the same time, we also found optical band gap decreases and photosensitivity of a-Si:H films increases with the increase of substrate temperature. So, the decrease of optical band gap and the increase of photosensitivity of a-Si:H films is the result of the decrease of hydrogen content, especially incorporated as polydride.