The Density of Gap States in Magnetron Sputtered Hydrogenated Amorphous Silicon

[摘要] The main objective of this project was to measure the density of states in magnetron sputtered hydrogenated amorphous silicon and compare it with that obtained from material prepared by the conventional R. F. sputtering method and to try to decide on the critical factors which may influence it. It was also intended to compare the results to the well known density of states of glow discharge amorphous silicon. To this end, two types of experiments were used: the admittance-frequency measurements on Schottky barriers and space charge limited current measurements. In the case of the Schottky barrier analysis, the results were analysed using a trap release model and the temperature-frequency dependence of the A. C. response of Schottky barriers was investigated. The results obtained from several samples give densities of states around 10e16 eV-1 cm-3 , significantly lower than the values quoted for non-magnetron material reported in literature. For SCLC experiment, the results obtained indicate densities of states near the fermi level of 10e15-10e16 eV -1cm-3 Experimental data showed that the surface layers at front and back contacts were different, clearly indicating surface properties of the film. Therefore, it becomes clear that a complete description of the material requires the surface states to be included in the analysis and a computer program was developed for this. It was concluded that the true bulk density of states of the material could be substantially reduced if surface states were considered. The temperature dependence of SCLC characteristics was also investigated and it was found that tail states could be detected by the SCLC technique. The values of the density of states obtained suggest that, as far as bulk properties of of magnetron sputtered a-Si:H are concerned, these are not distinguishable from those of glow discharge material. However, significant evidence was found for the presence of surface layers and their related effects.

[发布机构] University:University of Glasgow

[关键词] Condensed matter physics, Applied physics, Materials science