Radiatively Dominated Charge Carrier Recombination in Black Phosphorus

We show that black phosphorus is a highly efficient infrared emitter. To study the carrier dynamics, excess electron-hole pairs were generated in bulk black phosphorus by irradiation with 3 MeV electron pulses. The transient microwave conductivity due to excess charges was measured as a function of time for different initial charge densities at temperatures in the range 203-373 K. A new global analysis scheme, including the treatment of intrinsic carriers, is provided, which shows that the recombination dynamics in black phosphorus, a low bandgap semiconductor, is strongly influenced by the presence of intrinsic carriers. The temperature dependence of the charge mobility and charge carrier decay via second-order radiative recombination is obtained from modeling of the experimental data. The combined electron and hole mobility was found to increase with temperature up to 250 K and decrease above that. Auger recombination is negligible for the studied densities of excess electron-hole pairs up to 2.5 × 10¹⁷ cm^-3. For this density the major fraction of the excess electrons and holes undergoes radiative recombination. It is further inferred that for excess charge densities of the order of 10¹⁸ cm^-3 electrons and holes recombine with near unity radiative yield. The latter offers promising prospects for use of black phosphorus as efficient mid infrared emitter in devices.