Towards Room Temperature Plasmonic Lasing from Zn-Doped GaAs Nanowires*

We investigated optically pumped lasing from zinc-doped GaAs nanowires (NWs) on a Au film and from NWs comprising a nominally 10 nm thick Au coating at temperatures ranging from 80 to 295 K. The NWs have an average diameter and length of 200 nm and 2.5 µm, respectively, and possess a 7 nm thin Al₂O₃ spacer layer surrounding the NWs. The NWs were optically excited with 150 fs laser pulses with a center wavelength of 770 nm which were provided by a Ti-Sapphire laser. Due to the shortness of the NWs only one longitudinal lasing mode resonates with the gain spectrum which extends from ~1.48 to 1.52 eV at 80 K. At higher temperature the lasing mode slightly shifts towards lower energy and weakens due to band-gap shrinkage and increasing non-radiative losses at surface states. The lasing output versus excitation power (L-L) plot at 80 and 295 K shows the characteristic “S” shape curve for NWs on Au. The L-L plot for Au coated NWs shows lasing at 80 K but suggests amplified spontaneous emission at 295 K due to higher plasmonic losses. A simulation of the experimental data with FDTD calculations reveals that lasing from NWs on Au is predominantly plasmonic while it has a hybrid photonic-plasmonic character in Au coated NWs.