Metal-oxide based II-VI materials are of technological potential such as transparent conducting electrodes for optoelectronic devices. Particularly, ZnO is the most promising material due to its direct wide-bandgap of 3.37eV and a large exciton binding energy of 60meV at room temperatures. In case of undoped ZnO, its thin films have n-type conductivity because of intrinsic defects, such as oxygen vacancies and/or Zn interstitials. The thermal stability of the n-type conductivity of undoped ZnO, moreover, is poor and the electrical properties of undoped ZnO is also degraded at high temperatures, even though its crystallinity would be improved. Therefore, it is necessary that addition of the extrinsic source for n-type conductivity. Al-doped ZnO (AZO) thin films are considered as a substitute for indium tin oxide (ITO). However, dopant has an great affinity with oxygen than Zn atoms for the growth of Al-doped ZnO. So, that these oxide act as defects during the growth processes degrades the properties of thin films. Recently, It is reported that the properties of doped ZnO would be impoved by the post-annealing.
In this study, effects of the post-annealing on the microstructure of 2wt% Al-doped ZnO films were investigated. AZO films with about 300nm thickness were deposited on n-Si (001) substrate by rf magnetron sputtering method.
First, Increasing the annealing temperature, surface morphology was smooth and roughened again over 900℃. This is because it started that AZO films were evaporated into the vacuum over 900℃. In TEM observation of surface morphology for the AZO films annealed at 1000℃, relatively unstable facet planes were found dominantly, such as ($1\overline{1}01$), ($1\overline{2}12$), ($1\overline{2}16$).
In addition, bright-contrast region was formed in AZO films annealed at 900℃ and 1000℃. Using the tip to verify crystal or not, bright-contrast region was confirmed as amorphous phase. This amorphous phase also was formed in the AZO films annealed at 800℃ for 60min.
Lastly, zinc silicates such as $ZnSiO_3$ and $Zn_2SiO_4$ were formed near interfacial layer in all of the annealed AZO films. There are kinds of zince silicates. High-resolution images for monoclinic $ZnSiO_3$ and rhombohedral(r) $Zn_2SiO_4$ were obtained.
최근 모든 산업분야에서 투명 전도성 재료에 대한 관심이 크게 증가하고 그에 따른 고효율 고성능에 중점을 둔 재료의 중요성이 나날이 더해가고 있다. 그 중에서 ZnO는 3.37eV의 직접 천이형 밴드갭과 60emV의 큰 exciton binding energy를 갖는 화합물 반도체로 상업적인 응용분야에서 큰 관심이 모아지고 있다. ZnO는 재료 자체가 n-type 전도도를 갖지만, 안정적이지 못한 특성 때문에 다른 원소를 첨가하여 안정적인 n-type 전도도를 얻기 위한 연구들이 진행되고 있다. 그중에서도 대표적인 III족 원소를 도입한 Al-doped ZnO (AZO) 박막은 undoped-ZnO의 intrinsic n-type 전도도 및 안정성을 개선하고 기존의 ITO와 같은 투명전도성 산화막을 대체할 재료로써 크게 주목 받고 있다. 그리고 이러한 AZO 박막은 증착 후 열처리를 통하여 특성을 개선시키는 연구들이 진행되고 있다. 본 논문에서는 RF magnetron sputtering 법을 이용하여 n-Si (001) 기판 위에 성창시킨 AZO 박막을 전기적 및 광학적 성질 그리고 결정성을 향상시키기 위한 열처리 과정에서 나타날 수 있는 미세구조의 변화에 대하여 TEM을 이용하여 중점적으로 분석하였다.
