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

本研究以二乙基锌(DEZn)和水为反应气体，采用原子层沉积(ALD)法成功地制备了高质量的氧化锌TCO薄膜。在105-165的衬底温度范围内，第一次观察到了自限生长。由于ALD的自限幅特性，薄膜在大面积衬底上具有很好的均匀性，这表明ALD技术具有大规模生产氧化锌薄膜的能力。此外，在氧化锌的ALD中成功地使用了B_2H_6作为掺杂气体。通过掺硼改善了氧化锌薄膜的电学性能，对于厚度仅为400 nm的掺硼氧化锌薄膜，获得了12OmeGA的低方阻。为了获得织构和低阻的氧化锌薄膜，采用ALD和MOCVD技术相结合的两步法制备了氧化锌薄膜，并对其电学性能进行了研究。第一层用MOCVD方法生长，以获得四针状形貌，然后用ALD技术沉积第二层。通过在织构的MOCVD-ZnO薄膜上沉积低电阻率的AlD-ZnO薄膜，有效地改善了薄膜的电学和光学性能，同时保持了薄膜的织构表面形貌，并成功地将两步法制得的高质量的氧化锌薄膜应用于p-i-na-Si太阳电池的前接触。通过优化氧化锌薄膜的电学性质和表面形貌，在AM-1.5光照下，对于玻璃/氧化锌/p/缓冲器/i/n/氧化锌/银/铝结构的1cm2电池，获得了非常高的稳定转换效率，达到了8.2%。

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.