Kelvin probe study of band bending at organic semiconductor/metal interfaces: examination of Fermi level alignment
Kelvin probe study of band bending at organic semiconductor/metal interfaces: examination of Fermi level alignment
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DOI：
10.1002/pssa.200404346
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发表时间：
2004-05-01
影响因子：
2
通讯作者：
Seki, K
中科院分区：
文献类型：
--
作者：
Ishii, H;Hayashi, N;Seki, K
能带弯曲是讨论有机器件的一个基本问题。通常假设半导体和金属之间的费米能级对准的能带弯曲，尽管这种方案在有机半导体的情况下的有效性尚未建立。本文报道了我们最近用开尔文探针法（KPM）研究有机半导体能带弯曲的工作。在讨论了KPM对有机厚膜-金属衬底系统的适用性之后，给出了C-60、TPD和Alq（3）的结果，以讨论在真空条件下无故意掺杂的膜的能带弯曲。虽然空间电荷层的宽度在100 nm的量级，但对于C-60/金属界面观察到逐渐的能带弯曲。相比之下，TPD/金属界面观察到平带特征，可能是因为其纯度高。这些结果表明，在无机半导体界面中使用的能带弯曲的框架工作仍然是有效的有机半导体，虽然更厚的膜往往是必要的，以实现体费米能级对准。对于在暗条件下形成的Alq（3）/金属界面，我们发现了一种新的能带弯曲，其能级随离界面距离的线性变化。观察到的真空能级的位置远低于金属衬底的费米能级，清楚地表明费米能级在系统中的位置不同。这种电子非平衡状态在数年内相当稳定。费米能级排列的概念也讨论了所观察到的能量图。(C)2004 WILEY-VCH Verlag GmbH & Co. KGaA，魏因海姆。
Band bending is a fundamental issue for discussing organic devices. Band bending with Fermi level alignment between semiconductors and metals are often assumed, although the validity of this scheme in the case of organic semiconductors has been not yet established. In this paper, our recent efforts to examine band bending in organic semiconductors using Kelvin probe method (KPM) are reported. After discussing the applicability of KPM to organic thick film - metal substrate system, the results for C-60, TPD, and Alq(3) are shown to discuss band bending of the films without intentional doping in ultrahigh vacuum condition. Gradual band bending was observed for C-60/metal interfaces although the width of the space charge layer is in the order of 100 nm. In contrast, flat band feature was observed for TPD/metal interfaces probably because of its high purity. These results demonstrate that the frame work of band bending used in inorganic semiconductor interfaces is still valid for organic semiconductors although much thicker films are often necessary to achieve bulk Fermi level alignment. For Alq(3)/ metal interfaces formed in dark condition, we found a new type of band bending where the energy levels change as a linear function of the distance from the interface. The observed location of the vacuum level was far below the Fermi level of the metal substrates, clearly indicating that Fermi level varies place by place in the system. Such electronically non-equilibrium state was quite stable for the order of years. The concept of Fermi level alignment is also discussed in relation to the observed energy diagrams. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.