Development of ultra-uniform low-resistivity ZnO thin film by the atomic layer deposition

本研究以二乙基锌（DEZn）和H_2O为反应气体，采用原子层沉积（ALD）法成功地生长了高质量的ZnO TCO薄膜。自限性生长观察到，第一次，为基板温度范围从105至165。由于ALD的自限性特征，该膜在大面积衬底上具有非常好的均匀性，表明ALD技术能够用于大规模生产ZnO膜。用B_2H_2O_3成功地进行了硼掺杂。硼掺杂改善了ZnO薄膜的电学性能，并使ZnO薄膜的方块电阻率降低到12 OMEGA。对于厚度仅为400 nm的B掺杂ZnO薄膜，ALD法生长的ZnO薄膜在不同温度的真空退火和室温空气暴露条件下具有良好的电性能稳定性，表明ZnO薄膜具有较高的可靠性。为了获得具有织构和低电阻率的ZnO薄膜，提出了一种两步法工艺，该工艺将ALD和MOCVD技术相结合。通过MOCVD方法生长第一层以获得四脚状形态，然后使用ALD技术进行第二层沉积。通过在MOCVD-ZnO薄膜上沉积低电阻率的ALD-ZnO薄膜，有效地改善了ZnO薄膜的电学和光学性能，同时保持了ZnO薄膜的织构表面形貌，并将两步法制备的高质量ZnO薄膜成功地应用于p-i-na-Si太阳电池中作为前接触.通过优化ZnO薄膜的电学性能和表面形貌，在AM-1.5光照下，1cm ~ 2的玻璃/ZnO/p/buffer/i/n/ZnO/Ag/Al结构的电池获得了8.2%的稳定转换效率。

In this study, high-quality ZnO TCO films were successfully grown by atomic layer deposition (ALD) using diethylzinc (DEZn) and H_2O as reactant gases. Self-limiting growth was observed, for the first time, for substrate temperatures ranging from 105 to 165。C.The films had a very good uniformity over large area substrate due to the self-limiting feature of ALD, indicating the capability of ALD technique to be used for large-scale production of ZnO films.Furthermore, boron doping has successufully been carried out using B_2H_6 as a dopant gas in the ALD of ZnO.The electrical properties of ZnO films were improved by boron doping and a low sheet resistivity of 12OMEGA was obtained for B-doped ZnO film which was only 400nm thick. The ZnO films grown by ALD exhibited excellent stability in the electrical properties under the vacuum annealing at various temperatures and under air exposure at room temperature, indicating high reliability of the ZnO films.In order to obtain textured and low-resistivity ZnO films, a two-step process was proposed, which was carried out by combining the ALD and MOCVD techniques. The first layer was grown by the MOCVD method in order to obtain the tetrapod-like morphology, which was then followed by the second layer deposition using the ALD technique. The electrical and optical properties of ZnO films were effectively improved by depositing the lower resistivity ALD-ZnO films on to the textured MOCVD-ZnO films while the textured surface morphologies were well maintained.Finally, the obtained high-quality ZnO films by the two-step process were successfully applied to p-i-n a-Si solar cells as front contacts. Upon optimizing the electrical properties and surface morphologies of ZnO films, a very high stabilized conversion efficiency of 8.2% was obtained for the cell of 1cm2 with a structure of glass/ZnO/p/buffer/i/n/ZnO/Ag/Al under AM-1.5 illumination.