Department of Material Science and Engineering, University of Washington, Seattle, Washington 98195, USA.
Nat Commun. 2013;4:1474. doi: 10.1038/ncomms2498.
Monolayer group-VI transition metal dichalcogenides have recently emerged as semiconducting alternatives to graphene in which the true two-dimensionality is expected to illuminate new semiconducting physics. Here we investigate excitons and trions (their singly charged counterparts), which have thus far been challenging to generate and control in the ultimate two-dimensional limit. Utilizing high-quality monolayer molybdenum diselenide, we report the unambiguous observation and electrostatic tunability of charging effects in positively charged (X(+)), neutral (X(o)) and negatively charged (X(-)) excitons in field-effect transistors via photoluminescence. The trion charging energy is large (30 meV), enhanced by strong confinement and heavy effective masses, whereas the linewidth is narrow (5 meV) at temperatures <55 K. This is greater spectral contrast than in any known quasi-two-dimensional system. We also find the charging energies for X(+) and X(-) to be nearly identical implying the same effective mass for electrons and holes.
单层 VI 族过渡金属二卤族化合物作为半导体材料，正在取代石墨烯，其真正的二维特性有望为半导体物理带来新的启发。在此，我们研究了激子和电子空穴对（其单电荷对应物），迄今为止，在二维极限条件下，这两者的产生和控制都极具挑战性。我们利用高质量的单层二硒化钼，通过光致发光在场效应晶体管中明确观察到并能对带正电（X(+)）、中性（X(o)）和带负电（X(-)）激子的电荷效应进行静电可调谐。由于强限制和重有效质量，电子空穴对的荷电能量很大（30 毫电子伏特），而在<55 K 的温度下，线宽很窄（5 毫电子伏特）。这比任何已知的准二维系统都具有更大的光谱对比度。我们还发现 X(+)和 X(-)的荷电能量几乎相同，这意味着电子和空穴具有相同的有效质量。
