Metal–semiconductor ohmic contacts: An ab initio Density Functional Theory study of the structural and electronic properties of metal–diamond (111)-(1×1) interfaces

Ohmic contact between iridium film and hydrogen-terminated single crystal diamond

“…This p-type conduction layer has a sheet carrier density and mobility of 10 13  cm −2 and 50–150 cm 2 V −1 s −1 , respectively, nearly temperature-independent between 20 K and 300 K 17,18 . To enhance better performance of diamond electronic devices, an excellent ohmic contact between electrode metal layer and diamond is needed 9,19–24 . Up to now, many investigations of ohmic contact between metal and diamond have been reported, such as gold (Au), platinum (Pt) and palladium (Pd) on hydrogen-terminated single crystal diamond, all of which yield important role in diamond device development so far 9,25,26 .…”

Adhesion of the electrodes on diamond device surfaces

“…This is essential for establishing anti-peeling strength under high voltage and temperature that may occur in power devices. 2 A number of theoretical works have treated the adhesion between diamond surface and several metals, [18][19][20][21][22][23][24][25][26][27][28] but their exploration space were limited as shown here and hence there still exist the possibilities of discovering more appropriate electrode metals for diamond surfaces. Pickett and Erwin 18,20 were among the first to investigate metal/diamond interfaces for electronic device applications using first-principles local-density functional approaches, followed by the pioneering work on BN/diamond interfaces by Lambrecht and Segall.…”

“…Recent works [25][26][27][28] examined material structure model and studied several metals. Guo et al 25 On the other hand, Motochi et al 26 modeled the interfaces as periodic slabs comprised of monolayer metallic electrodes and ten-layer diamond surfaces with/without monolayer atomic terminations.…”

“…Recent works [25][26][27][28] examined material structure model and studied several metals. Guo et al 25 On the other hand, Motochi et al 26 modeled the interfaces as periodic slabs comprised of monolayer metallic electrodes and ten-layer diamond surfaces with/without monolayer atomic terminations. They applied density functional theory (DFT) approaches to evaluate adsorption energy, E ads and density of states (DOS) for their target systems.…”

Research status of metal/diamond interface

“…Wang 和 W.Wang 不同，他认为金、银、和铝分别与金刚石薄膜表面形成肖 特基接触 [14] 。也有研究者认为铬、钼和钽能与金刚石薄膜形成良好的欧姆接触 [15][16][17] 。目前， 研究者普遍认为碳基形成金属(即钛、铬、钽、钼和钒等)经过退火，能够与金刚石界面间 形成碳化物层，使之有较好的结合力，如图 6 所示。然而这些金属表面氧化会增加其表面阻 抗，所以再通过射频溅射或者化学蒸镀等方法在其表面覆盖一层金以提高其稳定性。钛也由 于其与金刚石接触的低阻抗，以及其向金刚石中较大的扩散度，使得其获得广泛的关注。 Yasushi Hoshino 等人通过对金/钛以及金/铂/钛两种金刚石表面的金属层热稳定性研究证实铂 中间层能够有效阻挡退火过程中钛向金层的扩散使得体系的接触电阻扩大的现象 [18] 。 图 4 金刚石表面金属层的压痕和划痕检测扫描电镜形貌图 (a)Ti/Cr/Au 表面压痕形貌(b)Ti/Cr/Au 表面划痕形貌 [19] 在对金属/金刚石的机械性能研究方面，主要采用纳米划痕仪与纳米压痕仪来对其界面的 结合性能进行检测，如图 4 所示为金刚石表面金属层的压痕和划痕检测扫描电镜形貌图。S. Msolli [20] 采用不同的方法制备出硅/铝和钛/铂/金两种金属吸附体系， 并分别对其机械性能进行 研究，并用纳米压痕仪来评估金属层之间的机械特性，利用纳米划痕仪来测定金属层与基底 的机械附着力，并采用扫描电镜对表面及压痕进行观察。结果表明，硅/铝界面的机械结合性 能较好，与之相反，钛/铂/金界面结合性能较差，出现剥落以及气泡等缺陷。该课题组随后采 用真空蒸镀的方法制备 Ti/Cr/Au 多层吸附， 其中 Ti、 Cr 和 Au 层的厚度分别为 0.03μm、 0.03μm 和 0.5μm。纳米划痕仪和纳米压痕仪的检测结果表明，Ti/Cr/Au 金属层与金刚石基底结合性 能好，没有剥落以及气泡等缺陷出现 [15] 。 也有研究者采用第一性原理计算的方法来对金属与金刚石间的结合性能以及导电性能进 行研究。 I. Motochi 等人 [21] 利用第一性原理为基础的 Quantum-ESPRESSO 软件对金刚石 (111) -(1×1)结构的无吸附、氢终端和氧终端的模型进行计算并在这三种模型表面吸附金、钛、 钽、钒和钯五种金属原子，对模型的平衡态几何结构，吸附能，态密度等结果进行了分析。 结果表明，金和钯在三种终端的结合力都弱于其他三种金属。Xiao-Gang Wang 等人 [22] 利用基 于密度泛函理论的全势线性缀加平面波方法(FLAPW) 研究了 Cu(111)/diamond(111)界面的结 合力，且分别研究了金刚石表面单悬键和三悬键的情况，经过对比分析，研究者认为氢会减 弱铜和金刚石表面的结合强度，且氢在铜/金刚石界面能够稳定存在。Haibo Guo 等研究者 [23] 采用基于密度泛函理论的…”