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首页> 外文期刊>Journal of Physics, D. Applied Physics: A Europhysics Journal >Comparison of the electronic structure of amorphous versus crystalline indium gallium zinc oxide semiconductor: structure, tail states and strain effects
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Comparison of the electronic structure of amorphous versus crystalline indium gallium zinc oxide semiconductor: structure, tail states and strain effects

机译：非晶铟与晶体铟镓锌氧化物半导体的电子结构比较：结构，尾态和应变效应

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摘要

We study the evolution of the structural and electronic properties of crystalline indium gallium zinc oxide (IGZO) upon amorphization by first-principles calculation. The bottom of the conduction band (BCB) is found to be constituted of a pseudo-band of molecular orbitals that resonate at the same energy on different atomic sites. They display a bonding character between the s orbitals of the metal sites and an anti-bonding character arising from the interaction between the oxygen and metal s orbitals. The energy level of the BCB shifts upon breaking of the crystal symmetry during the amorphization process, which may be attributed to the reduction of the coordination of the cationic centers. The top of the valence band (TVB) is constructed from anti-bonding oxygen p orbitals. In the amorphous state, they have random orientation, in contrast to the crystalline state. This results in the appearance of localized tail states in the forbidden gap above the TVB. Zinc is found to play a predominant role in the generation of these tail states, while gallium hinders their formation. Last, we study the dependence of the fundamental gap and effective mass of IGZO on mechanical strain. The variation of the gap under strain arises from the enhancement of the anti-bonding interaction in the BCB due to the modification of the length of the oxygen-metal bonds and/or to a variation of the cation coordination. This effect is less pronounced for the amorphous material compared to the crystalline material, making amorphous IGZO a semiconductor of choice for flexible electronics. Finally, the effective mass is found to increase upon strain, in contrast to regular materials. This counterintuitive variation is due to the reduction of the electrostatic shielding of the cationic centers by oxygen, leading to an increase of the overlaps between the metal orbitals at the origin of the delocalization of the BCB. For the range of strain typically met in flexible electronics, the induced variation in the effective mass is found to be negligible (less than 1%).
机译：我们通过第一性原理计算研究了非晶化后结晶铟镓锌氧化物（IGZO）的结构和电子性能的演变。发现导带（BCB）的底部由分子轨道的伪带构成，该伪带在不同原子位点以相同能量共振。它们显示出金属位点s轨道之间的键合特征，以及由于氧和金属s轨道之间的相互作用而产生的反键合特征。在非晶化过程中，随着晶体对称性的破坏，BCB的能级发生变化，这可能归因于阳离子中心配位的降低。价带（TVB）的顶部由抗键氧p轨道构成。与结晶态相反，在非晶态中，它们具有随机取向。这导致在TVB上方的禁止间隙中出现局部尾态。发现锌在这些尾态的产生中起主要作用，而镓则阻碍了它们的形成。最后，我们研究了IGZO的基本间隙和有效质量对机械应变的依赖性。由于应力-金属键长度的改变和/或阳离子配位的变化，在应力作用下间隙的变化是由于BCB中抗键相互作用的增强所致。与结晶材料相比，非晶材料的影响不那么明显，这使得非晶IGZO成为柔性电子产品的首选半导体。最后，与常规材料相比，发现有效质量随着应变而增加。这种违反直觉的变化是由于氧对阳离子中心的静电屏蔽作用降低，导致金属轨道之间的重叠在BCB离域的起点处增加。对于柔性电子设备中通常满足的应变范围，发现有效质量的感应变化可以忽略不计（小于1％）。

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