单层二维材料WSe2的生长机制与MoS2/WSe2异质结构的制备

Two dimensional transition metal dichalcogenides(TMDCs) are a family of materials which processes unique electronic properties for various optoelectronic device applications. One of the well known TMDCs is the n type semiconducting MoS2, which have attracted intensive research interests. High quality MoS2 monolayer film have been synthesized over a large area and have been testified for exciting electronic, sensor and biomedical applications. Yet its application in p-n junction, i.e., to couple with a heterostructured material, has been achieved over a large area. Indeed, the challenge remains because of the limited lateral size of the most suitable p type semiconducting counterpart tungsten diselenide (WSe2). Through the common preparation approaches, e.g., mechanical exfoliation, chemical exfoliation and thermal deposition, the WSe2 isolated flakes or domains have been synthesized, with the typical lateral width of 50 micrometers. For a very long time, this disadvantage has limited the development of p type TMDCs, i.e., this is not compatible with conventional semiconducting industry. Therefore large area synthesis technique is of high importance for the patterning of two dimensional heterostructure. Hence, in this proposal, we use the chemical vapor deposition for the synthesis of centimeter scale WSe2 monolayer film, including its early stage nucleation, growth mechanism and the thermodynamics and kinetics during the growth stage. Also we use Monte Carlo Simulation and molecular dynamics for the understanding of growth mechanism as well as optimized parameters. We aimed at optimization of growth parameter space with the catalyst, temperature and gases to achieve enlarged domain size of WSe2. In addition, we use the pre-deposition of seed to nucleate the domains in patterned arrays. Eventually, we test the optoelectronics application such as near infrared photo detectors. Next we integrate the p type WSe2 with n-type MoS2 to achieve the atomic layer thick p-n junction and device application.

二维过渡金属二硫族化合物(TMDCs)家族，具有独特的电子特性，例如n型半导体导电的二硫化钼，已实现大面积高质量的单层膜的制备，并且在电子、传感和生物医学等领域上得到了广泛应用。而光电器件，需要通过p-n结来实现。而最与之匹配的p型半导体材料是同家族的二硒化钨(WSe2)，用常用的机械或化学剥离法以及热沉积法制备的晶畴尺寸很小，在几十微米以内。这会限制p-n结的尺寸，不利于与大规模生产的半导体工艺兼容。大面积的制备技术，有利于异质结的阵列化制备，有重要的意义。因此，本研究着重于厘米级的二硒化钨薄膜的早期形核、生长机理及其反应过程中的热力学和动力学。本研究采用化学气相沉积法，通过蒙特卡洛模拟以及分子动力学模拟，来预测并指导实验，获得优化的催化剂、温度等条件，增大晶畴尺寸。下一步，辅助以图案化预埋籽晶来实现图案化的晶畴生长。大规模高质量的材料，将用于探索光电器件比如近红外光探测器的应用。

二维材料及其范德华异质结等新兴材料表现出独特的声、光、电、磁等物理化学性质，是红外光探测器、逻辑门电路与数据存储器等器件理想的半导体功能材料。与传统硅工艺技术相比，显著降低晶体管数目并提升芯片面积使用率，具有广阔前景。本项目开展了以下研究内容：1. 钨前驱体薄膜的合成生长机理研究；2. 化学气相沉积法中二硒化钨的成核与生长机理研究；3. 二维材料硫化铂的生长机制研究；4. 金属硫族化合物的结构与能带调控研究；5. 二硒化钨材料的电输运性质及场效应晶体管性能；6. 二硒化钨及硫化铂二维材料的光探测器及光电性能研究。重要结果有：（1）发展了一种预埋籽晶策略，即浸涂衬底沉积上的氧化钨，起到了预埋籽晶的效果，用于实现均匀的大面积单层二硒化钨全覆盖薄膜的制备。高质量的WSe2薄膜提高了场效应晶体管的电荷输运性能和光电探测器响应度性能。（2）利用金属-后硫化策略，实现了4英寸晶圆级金属硫化物硫化铂的成功制备。（3）设计实现了金属硫硒化物薄膜（硫化锑、硫硒化锑和硒化锑三叠层）中能带排列的梯度，促进了电荷载流子的产生和分离，这验证了金属硫硒化物三结串联太阳能电池设计的先进性。关键数据及科学意义：二硒化钨基晶体管载流子迁移率为276 cm2 ·V−1 ·s−1，达到国际先进水平。首次获得材料制备的热力学数据活化能为： 2.95 eV （生长速率）和5.55 eV（晶畴密度）。首次报道了4英寸晶圆级硫化铂的成功制备，提供了硫化铂的相图，为过渡金属硫族化合物的制备提供了一般性普适策略；蓝宝石衬底上的PtS器件的探测率为9.17×109 Jones，响应率为0.31 A W-1, 外部量子效率EQE为66.45%。依据能带对准设计的金属硫族化合物基三叠层太阳能电池获得了理论光电转换效率32.98%，该能带对准的一般方法为提高多p-n结太阳能电池的转换效率提供重要参考。项目资助下发表InfoMat等文章20篇，参加国际学术会议4次，培养硕士研究生3人，为后续的二维材料及异质结构研究提供了扎实的技术基础，对大规模化生产有重要的启发意义。