High quality electrical contact to semiconducting transition metal dichalcogenides (TMDCs) such as MoS₂ is key to unlocking their unique electronic and optoelectronic properties for fundamental research and device applications. Despite extensive experimental and theoretical efforts reliable ohmic contact to doped TMDCs remains elusive and would benefit from a better understanding of the underlying physics of the metal–TMDC interface. Here we present measurements of the atomic-scale energy band diagram of junctions between various metals and heavily doped monolayer MoS₂ using ultrahigh vacuum scanning tunneling microscopy (UHV-STM). Our measurements reveal that the electronic properties of these junctions are dominated by two-dimensional metal-induced gap states (MIGS). These MIGS are characterized by a spatially growing measured gap in the local density of states (L-DOS) of the MoS₂ within 2 nm of the metal–semiconductor interface. Their decay lengths extend from a minimum of ∼0.55 nm near midgap to as long as 2 nm near the band edges and are nearly identical for Au, Pd, and graphite contacts, indicating that it is a universal property of the monolayer semiconductor. Our findings indicate that even in heavily doped semiconductors, the presence of MIGS sets the ultimate limit for electrical contact.

中文翻译：

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金属和高掺杂单层MoS ₂的界面处没有带隙

与半导体过渡金属二硫化碳（TMDC）（例如MoS ₂）的高质量电接触是为基础研究和设备应用解锁其独特的电子和光电特性的关键。尽管进行了广泛的实验和理论努力，与掺杂TMDC的可靠欧姆接触仍然难以捉摸，并且将从对金属-TMDC接口的基本物理原理的更好理解中受益。在这里，我们介绍了各种金属与重掺杂单层MoS ₂之间的结的原子尺度能带图的测量结果使用超高真空扫描隧道显微镜（UHV-STM）。我们的测量结果表明，这些结的电子特性主要由二维金属诱导的间隙态（MIGS）决定。这些MIGS的特征在于，在金属-半导体界面的2 nm范围内，MoS ₂的局部态密度（L-DOS）中的空间测量间隙不断增大。它们的衰减长度从中能隙附近的最小〜0.55 nm延伸到能带边缘附近的2 nm，并且对于Au，Pd和石墨接触几乎相同，这表明它是单层半导体的通用特性。我们的发现表明，即使在重掺杂半导体中，MIGS的存在也为电接触设置了极限。