Depth analysis of subgap electronic states in amorphous oxide semiconductor, a-In-Ga-Zn-O, studied by hard x-ray photoelectron spectroscopy
Depth analysis of subgap electronic states in amorphous oxide semiconductor, a-In-Ga-Zn-O, studied by hard x-ray photoelectron spectroscopy
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DOI：
10.1063/1.3560769
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发表时间：
2011-04-01
影响因子：
3.2
通讯作者：
Hosono, Hideo
中科院分区：
文献类型：
--
作者：
Nomura, Kenji;Kamiya, Toshio;Hosono, Hideo
在先前的工作中，我们用硬X射线光电子能谱（HX-PES）研究了高掺杂非晶In-Ga-Zn-O（a-IGZO）薄膜中的亚带隙态，发现它们具有高于价带顶（VBM）的亚带隙电子态，密度> 5 × 10（20）cm（-3），而密度> 5 × 10（19）cm（-3）的亚带隙电子态则刚好低于费米能级[K.野村（Nomura，T. Kamiya，H. Yanagi，E.池永湾Yang，K.小林，M. Hirano和H.细野，应用物理学快报。92，202117（2008）];然而，它们的电子密度（N-e > 3 × 10（19）cm（-3））相当高，并且与薄膜晶体管（TFT）中的有源沟道层所需的合理性质不相容。在这项工作中，我们报告的影响，N-电子和热退火的subgap态，以提供数据，为实际的TFT有用。发现低N-e的a-IGZO薄膜在VBM以上具有额外的亚带隙态，类似于先前的报道，但是对于高电阻的湿法退火的a-IGZO薄膜，它们的密度小到类似于2.0 × 10（20）cm（-3）。角度相关的HX-PES显示，VBM以上的亚能隙态集中在表面区域。O 1 s峰表明，湿退火抑制产生的亚带隙态终止这些国家与-OH键。在ZnO、（c-）IGZO和a-IGZO中普遍观察到低于E-F的亚能隙态。可以得出结论，这些低于E-F的状态既不与a-IGZO的无序结构有关，也不与它们的TFT特性有关。认为这些态与高能光子在真空中产生的亚稳态有关。(C)2011年美国物理学会。[doi：10.1063/1.3560769]
In a previous work, we examined subgap states in highly doped amorphous In-Ga-Zn-O (a-IGZO) films by hard x-ray photoelectron spectroscopy (HX-PES) and found they had subgap electronic states above the valence band maximum (VBM) with the densities > 5 x 10(20) cm(-3) and just below the Fermi level with the densities > 5 x 10(19) cm(-3) [K. Nomura, T. Kamiya, H. Yanagi, E. Ikenaga, K. Yang, K. Kobayashi, M. Hirano, and H. Hosono, Appl. Phys. Lett. 92, 202117 (2008)]; however, their electron densities (N-e > 3 x 10(19) cm(-3)) are rather high and not compatible with rational properties required for active channel layers in thin-film transistors (TFTs). In this work, we report the effects of N-e and thermal annealing on the subgap states in order to provide the data useful for actual TFTs. It was found that the low-N-e a-IGZO films had extra subgap states above VBM similar to the previous report, but their densities were as small as similar to 2.0 x 10(20) cm(-3) for the highly resistive, wet-annealed a-IGZO films. Angle-dependent HX-PES revealed that the subgap states above VBM concentrate in the surface region. The O 1s peak indicated that the wet annealing suppressed the generation of subgap states by terminating these states with -OH bonds. The subgap states below E-F were observed commonly in all the samples including ZnO, crystalline (c-) IGZO and a-IGZO. It is concluded that these states below E-F are neither related to the disordered structures of a-IGZO nor to their TFT characteristics. It is considered that these states are related to the metastable states created by the high-energy photons in vacuum. (C) 2011 American Institute of Physics. [doi:10.1063/1.3560769]