高质量ε相氧化镓单晶薄膜的金属有机化学气相异质外延生长研究

Following the development of gallium nitride and silicon carbide in the past decades, gallium oxide arises as the most promising next-generation semiconductor for power electronics because of its ultra-wide bandgap of 4.9eV. However, due to the special crystal structure and the poor heat dissipation ability of gallium oxide, effective method have not yet been established for the preparation of the gallium oxide single-crystalline thin film. Therefore, this project proposes a new resolution in which hexagonal ε-phase gallium oxide (ε-Ga2O3) single-crystallinel thin films are grown on sapphire substrates by heteroepitaxy. In the framework of metal organic chemical vapor deposition (MOCVD) two-step growth method, by carefully modulating the growth conditions and analyzing the growth mechanism, we will induce a growth mode transition of hexagonal ε-Ga2O3 from three-dimensional to two-dimensional. Meanwhile, doping experiments of N-type ε-Ga2O3 thin films will also be carried out. The prepared single-crystalline films are characterized by low roughness ("step flow" surface morphology), high crystalline quality (threading dislocation, stacking fault density not higher than 10^8 / cm^2) and controllable conductance. This will provide a practical, efficient and economical technical route for the preparation of high quality gallium oxide single-crystalline thin films, which greatly promotes the potential of the gallium oxide semiconductor in the application of high-power electronics.

氧化镓以其4.9eV的超宽带隙，成为继氮化镓、碳化硅之后，最具有应用前景的新一代功率电子器件半导体材料。但由于氧化镓晶型结构特殊、各向异性显著、材料热导率差，所以目前对用于电子器件的氧化镓单晶薄膜，仍未有有效的制备方案。鉴于此，本项目提出基于蓝宝石衬底的六方晶系ε相氧化镓（ε-Ga2O3）单晶薄膜异质外延的技术方案：采用金属有机化学气相沉积（MOCVD）的经典两步生长法，通过调控生长条件、构建生长模型，诱导ε-Ga2O3的生长模式从三维转化为二维，形成单晶薄膜；同时，还将开展N型ε-Ga2O3薄膜的掺杂研制。所制得的单晶薄膜具有低粗糙度（实现“台阶流”表面形貌）、高结晶质量（实现位错、层错缺陷密度不高于10^8/cm^2）、电导可控的特点。本项目最终将为高质量氧化镓单晶薄膜的制备，提供一条高效、低成本的技术路线，极大的推动氧化镓半导体作为功率电子器件材料的实用化进程。

本项目通过采用MOCVD两步生长法，实现了基于2~4英寸蓝宝石衬底的高质量ε-Ga2O3单晶薄膜异质外延生长；所制备的薄膜样品均能实现“台阶流”表面形貌（粗糙度低于1nm）；样品具有高结晶质量，典型样品的位错密度在4.8×10^7~1.1×10^8/cm2范围；非掺杂样品的背景电子浓度最低约为5×10^15/cm3；N型掺杂样品的电子浓度最高可达6×10^19 /cm3，迁移率为96 cm2/Vs。项目执行期间，一些研究成果产生了重要的影响和价值：首先，由于ε-Ga2O3缺乏单晶衬底，异质外延是制备ε-Ga2O3单晶薄膜的唯一方法，而本项目制备的ε-Ga2O3单晶薄膜，相比国内外其他研究团队的报道结果，具有更高的结晶质量，处于领先地位；其次，利用MOCVD方法，实现在低成本蓝宝石衬底上的大尺寸（4英寸）单晶外延，对新型氧化镓半导体材料的低成本大尺寸制备具有重要的参考意义；最后，团队研发并成功制备出国内外首个ε-Ga2O3-MOSFET器件，从实验上验证了ε-Ga2O3半导体器件制备的可行性。项目的实施成果，将为高质量氧化镓薄膜的制备提供一条实用高效、低成本、且具有我国自主知识产权的新技术路线，提升氧化镓材料在功率电子器件中的应用潜力。