Deep level transient spectroscopy on light-emitting diodes based on (In,Ga)N/GaN nanowire ensembles

摘要

Ⅲ-N nanowires (NWs) are an attractive alternative to conventional planar layers as the basis for light-emitting diodes (LEDs). In fact, the NW geometry enables the growth of (In,Ga)N/GaN heterostructures with high indium content and without extended defects regardless of the substrate. Despite these conceptual advantages, the NW-LEDs so far reported often exhibit higher leakage currents and higher turn-on voltages than the planar LEDs. In this work, we investigate the mechanisms responsible for the unusually high leakage currents in (In,Ga)N/GaN LEDs based on self-induced NW ensembles grown by molecular beam epitaxy on Si substrates. The temperature-dependent current-voltage (Ⅰ-Ⅴ) characteristics, acquired between 83 and 403 K, reveal that temperatures higher than 240 K may activate a further conduction process, which is not present in the low temperature range. Deep level transient spectroscopy (DLTS) measurements show the presence of electron traps, which are activated in the same temperature interval. A detailed analysis of the DLTS signal reveals the presence of two distinct deep levels with apparent activation energies close to E_c-570 meV and E_c-840 meV, and capture cross sections of about 1.0×10~(-15) cm~2 and 2×10~(-14) cm~2, respectively. These results suggest that the leakage process might be related to trap-assisted tunneling, possibly produced by point defects located in the core and/or on the sidewalls of the NWs.