Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA, USA.
Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, CA, USA.
Nature. 2021 Nov;599(7885):404-410. doi: 10.1038/s41586-021-03949-7. Epub 2021 Nov 17.
Two-dimensional (2D) semiconductors have attracted intense interest for their unique photophysical properties, including large exciton binding energies and strong gate tunability, which arise from their reduced dimensionality. Despite considerable efforts, a disconnect persists between the fundamental photophysics in pristine 2D semiconductors and the practical device performances, which are often plagued by many extrinsic factors, including chemical disorder at the semiconductor-contact interface. Here, by using van der Waals contacts with minimal interfacial disorder, we suppress contact-induced Shockley-Read-Hall recombination and realize nearly intrinsic photophysics-dictated device performance in 2D semiconductor diodes. Using an electrostatic field in a split-gate geometry to independently modulate electron and hole doping in tungsten diselenide diodes, we discover an unusual peak in the short-circuit photocurrent at low charge densities. Time-resolved photoluminescence reveals a substantial decrease of the exciton lifetime from around 800 picoseconds in the charge-neutral regime to around 50 picoseconds at high doping densities owing to increased exciton-charge Auger recombination. Taken together, we show that an exciton-diffusion-limited model well explains the charge-density-dependent short-circuit photocurrent, a result further confirmed by scanning photocurrent microscopy. We thus demonstrate the fundamental role of exciton diffusion and two-body exciton-charge Auger recombination in 2D devices and highlight that the intrinsic photophysics of 2D semiconductors can be used to create more efficient optoelectronic devices.
二维（2D）半导体因其独特的光物理性质而引起了极大的兴趣，包括大激子结合能和强栅极可调谐性，这源于其维度的降低。尽管已经付出了相当大的努力，但在原始 2D 半导体的基本光物理和实际器件性能之间仍然存在脱节，而实际器件性能往往受到许多外在因素的困扰，包括半导体-接触界面的化学无序。在这里，通过使用具有最小界面无序的范德华接触，我们抑制了接触诱导的肖克利-里德-霍尔复合，并在 2D 半导体二极管中实现了几乎由本征光物理决定的器件性能。我们在分裂栅几何结构中使用静电场来独立地调节二硒化钨二极管中的电子和空穴掺杂，发现短路光电流在低电荷密度下出现异常峰值。时间分辨光致发光揭示了由于激子-电荷俄歇复合的增加，在电荷中性区域中激子寿命约为 800 皮秒，而在高掺杂密度下激子寿命约为 50 皮秒，从而显著降低了激子寿命。总之，我们表明，激子扩散限制模型很好地解释了电荷密度依赖的短路光电流，这一结果通过扫描光电流显微镜进一步得到了证实。因此，我们证明了激子扩散和双体激子-电荷俄歇复合在 2D 器件中的基本作用，并强调了 2D 半导体的本征光物理可以用于创建更高效的光电设备。
