氢终端金刚石薄膜生长及其表面结构

Growth and surface structrue of hydrogen terminal diamond thin films

氢终端金刚石的导电性问题是目前限制其在器件领域应用的关键因素.传统的氢终端金刚石制备工艺由于金刚石中含有杂质元素以及表面的加工损伤的存在,限制了氢终端金刚石的电特性.在金刚石衬底上直接外延一层高纯、表面平整的氢终端金刚石薄膜成为一种可行方案,但该方案仍存在薄膜质量表征困难,表面粗糙度较大等问题.本文采用微波等离子体化学气相沉积(CVD)技术,在含氮CVD金刚石衬底上外延一层亚微米级厚度金刚石薄膜,并研究分析了不同甲烷浓度对金刚石薄膜生长以及导电性能的影响.测试结果显示:金刚石薄膜生长厚度为230—810 nm,且外延层氮浓度含量低于1×10^(16) atom/cm^(3),不同的甲烷浓度生长时,金刚石外延层表面出现了三种生长模式,这主要与金刚石的生长和刻蚀作用相关.经过短时间生长后的金刚石薄膜表面为氢终端(2×1:H)结构,而氧、氮元素在其中的占比极低,这使得生长后的金刚石薄膜具有P型导电特性.霍尔测试结果显示,甲烷浓度为4%条件下生长的氢终端金刚石薄膜导电性最好,其方块电阻为4981Ω/square,空穴迁移率为207 cm^(2)/(V·s),有效地提升了氢终端金刚石电特性,为推进大功率金刚石器件发展应用起到支撑作用.

The conductivity of hydrogen-terminated diamond is a limiting factor in its application in field-effect transistor devices.The traditional preparation process hinders the improvement of the electrical properties of hydrogen-terminated diamond due to impurity elements in the diamond bulk and surface damage caused by processing near the diamond surface.To overcome this,researchers have explored the epitaxial growth of a high-purity and flat-surfaced diamond thin film on a diamond substrate.However,this approach still faces challenges in film characterization and achieving high surface smoothness.In this study,microwave plasma chemical vapor deposition technology is used to epitaxially grow a sub-micron thick diamond film on a nitrogendoping chemical vapor deposition diamond substrate of 10 mm×10 mm×0.5 mm in size.The influence of methane concentration on the growth and conductivity of diamond film is investigated.The test results reveal that the growth thickness of the diamond film ranges from 230 to 810 nm,and the nitrogen concentration in the epitaxial layer is lower than 1×10^(16) atom/cm^(3).Three growth modes are observed for the homoepitaxial growth of the diamond thin film under different methane concentrations.A methane concentration of 4%enables twodimensional planar growth of diamond,resulting in a smooth and flat surface with a roughness of 0.225 nm(10μm×10μm).The formation of different surface morphologies is attributed to the growing process and etching process of diamond.Surface low-energy electron diffraction testing indicates that the surface of the diamond film undergoes a structural transition from oxygen terminal(1×1:O)to hydrogen terminal(2×1:H)when grown for a short period of time.X-ray photoelectron spectroscopy analysis reveals an extremely low ratio of oxygen element to nitrogen element,giving the grown diamond film P-type conductivity characteristics.The Hall test results demonstrate that the hydrogen-terminated diamond film grown with a methane concentration of 4% exhibits the highest conductivity,with a square resistance of 4981Ω/square and a hole mobility of 207 cm^(2)/(V·s).This enhanced conductivity can be attributed to the lower defect density observed under these specific conditions.The findings of this study effectively improve the electrical properties of hydrogen-terminated diamond,and contribute to the development and practical application of high-power diamond devices.