摘要:
宽带隙半导体金刚石具有突出的电学与热学特性,近年来,基于金刚石的儈频大功率器件受到广泛关注,对于金属-金刚石肖特基结而言,具有较儈的击穿电压和较小的串联电阻,所以金属-金刚石这种金半结具有非常好的发展前景.本文通过第一性原理方法去研究金属铝-金刚石界面电子特性与肖特基势垒的儈度.界面附近原子轨道的投影态密度的计算表明:金属诱导带隙态会在金刚石一侧产生,并且具有典型的局域化特征,同时可以发现电子电荷转移使得Fermi能级在金刚石一侧有所提升.电子电荷在界面的重新分布促使界面形成新的化学键,使得金属铝-氢化金刚石形成稳定的金半结.特别地,我们通过计算平均静电势的方法得到金属铝-氢化金刚石界面的势垒儈度为1.03 eV,该值与金属诱导带隙态唯像模型计算的结果非常接近,也与实验值符合得很好.本文的研究可为金属-金刚石肖特基结二极管的研究奠定理论基础,也可为金刚石基金半结大功率器件的研究提供理论参考.
Abstract:
Diamond is regarded as one of the most promising semiconductor materials used for high power devices because of its superior physical and electrical properties, such as wide bandgap, high breakdown electric field, high mobility, and high thermal conductivity. Highpower diamond devices are now receiving much attention. In particular, Schottky diode based on a metal/diamond junction has promising applications, and high breakdown voltage has been achieved, though unfortunately its forward resistance is high. In this paper, the first principles calculations are performed to study the electronic structure of interface and the Schottky barrier height of Al-diamond interface. The projection of the density of states on the atomic orbitals of the interface atoms reveals that the typical Al-induced gap states are associated with a smooth density of states in the bulk diamond band gap region, and these gap states are found to be localized within three atom layers. At the same time, electronic charge transfer makes the Fermi level upgrade on the side of diamond. Besides, the typical Al-induced gap state model gives a simple picture about what determines Schottky barrier height at Al-diamond interface, by assuming an ideal, defect-free and laterally homogeneous Schottky interface in which the only interaction comes from the decay of the electron wave function from the metal into the semiconductor, which in turn induces electronic charges to be rearranged in the region close to the interface. As for the electronic charge transfer, this potential shift can be extracted by subtracting the superimposed planar or macroscopically averaged electrostatic potentials of the Al and diamond surfaces (at frozen atomic positions), from the planar or macroscopically averaged potential of the relaxed Al-diamond interface. The electronic charge transfer suggests that the formation of an interface should be associated with the formation of new chemical bonds and substantial rearrangements of the electron charge density. Especially, we obtain the Schottky barrier height of 1.03 by the first principle, which is in good agreement with the results from phenomenological model and experiment. The research results in this paper can provide a theoretical basis for the research of the metal diamond Schottky junction diode, and can also give a theoretical reference for the research of the metal-semiconductor highpower device based on diamond material.
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