Wafer-Scale Epitaxial Growth of Unidirectional WS2 Monolayers on Sapphire
Wafer-Scale Epitaxial Growth of Unidirectional WS2 Monolayers on Sapphire
复制标题
DOI：
10.1021/acsnano.0c06750
复制
发表时间：
2021-01-15
期刊：
影响因子：
17.1
通讯作者：
Redwing, Joan M.
中科院分区：
文献类型：
--
作者：
Chubarov, Mikhail;Choudhury, Tanushree H.;Redwing, Joan M.
过渡金属二硫属化物（TMD）如WS 2的晶片级单晶膜的实现需要取向畴的外延生长和聚结以形成连续单层。畴必须在衬底上以相同的晶体学方向取向，以抑制反转畴边界（IDB）的形成，反转畴边界是层状硫属化物的共同特征。在这里，我们展示了完全合并的单向WS 2单层2英寸。通过使用多步生长工艺的金属有机化学气相沉积来制备直径为c平面的蓝宝石，以获得具有低平面内旋转扭曲（0.09度）的外延WS 2单层。透射电子显微镜分析表明，WS 2单层在很大程度上是免费的IDBs，而是有平移边界时出现的WS 2域稍微偏移晶格合并在一起。通过调节单层生长速率，平移边界的密度和双层覆盖率显着降低。域的单向取向归因于蓝宝石表面上的台阶的存在，其与促进表面扩散、横向域生长和聚结同时保持对准的域结构的生长条件相结合。转移WS 2单层显示中性和带电激子发射在80 K与可忽略不计的缺陷相关的发光。背栅WS 2场效应晶体管表现出类似于10（7）的I-ON/（OFF）和16 cm（2）/（Vs）的迁移率。结果表明，实现晶片级TMD单层无反转域的性能接近剥离片的潜力。
Realization of wafer-scale single-crystal films of transition metal dichalcogenides (TMDs) such as WS2 requires epitaxial growth and coalescence of oriented domains to form a continuous monolayer. The domains must be oriented in the same crystallographic direction on the substrate to inhibit the formation of inversion domain boundaries (IDBs), which are a common feature of layered chalcogenides. Here we demonstrate fully coalesced unidirectional WS2 monolayers on 2 in. diameter c-plane sapphire by metalorganic chemical vapor deposition using a multistep growth process to achieve epitaxial WS2 monolayers with low in-plane rotational twist (0.09 degrees). Transmission electron microscopy analysis reveals that the WS2 monolayers are largely free of IDBs but instead have translational boundaries that arise when WS2 domains with slightly offset lattices merge together. By regulating the monolayer growth rate, the density of translational boundaries and bilayer coverage were significantly reduced. The unidirectional orientation of domains is attributed to the presence of steps on the sapphire surface coupled with growth conditions that promote surface diffusion, lateral domain growth, and coalescence while preserving the aligned domain structure. The transferred WS2 monolayers show neutral and charged exciton emission at 80 K with negligible defect-related luminescence. Back-gated WS2 field effect transistors exhibited an I-ON/(OFF) of similar to 10(7) and mobility of 16 cm(2)/(Vs). The results demonstrate the potential of achieving wafer-scale TMD monolayers free of inversion domains with properties approaching those of exfoliated flakes.