Widely Tunable Mid-Infrared Light Emission in Thin-Film Black Phosphorus*

In this work, we report the widely tunable mid-infrared light emission from dual-gate hexagonal boron nitride (hBN)/Black Phosphorus (BP)/hBN heterostructure devices. The photoluminescence (PL) from a ~20-layer BP flake can be continuously tuned from 3.7 to 7.7 μm with a moderate displacement field of 0.48 V/nm, spanning 4 μm in mid-infrared. The PL emission remains perfectly linear-polarized regardless of the bias field due to the preservation of the optical transition rule. We further performed first-principles calculation to investigate the gate dependence of the band structure and optical conductivity in BP. Moreover, together with theoretical analysis we show that the radiative decay probably dominates over other nonradiative decay channels in the PL experiments. Our results reveal the great potential of thin-film BP in widely tunable, mid-infrared light emitting and lasing applications.