Ultra-Low Power Light Emission via Avalanche and Sub-avalanche Breakdown in Suspended Carbon Nanotubes

We explore near-infrared light emission in suspended carbon nanotube field effect transistors over a wide range of gate and bias voltages. An abrupt increase in both the electric current (90 mu A/V) and electroluminescence intensity is observed at high bias voltages (similar to 3.5 V), when gated in the "off" state (i.e., V-gate > 0 V). For bias voltages below the threshold for avalanche breakdown, we observe light emission due to the creation of exitons by impact ionization under these high electric fields. Here, we find that there is a relatively small region over which low power (similar to nW) light emission is observed. By plotting the relative luminescence efficiency (i.e., light intensity/electrical power) as a function of the gate and bias voltages, we observe a very sharp feature corresponding to avalanche emission at which the electroluminescence efficiency is 2-3 orders of magnitude higher than that under all other conditions of gate and bias voltage. A steep increase in the current with bias voltage (i.e., large dI/dV(b)) is observed at the same gate and bias conditions of the highly efficient electroluminescence and signifies the onset of the avalanche process. We believe that these results demonstrate additional mechanistic evidence for achieving highly efficient light emission in carbon nanotubes via avalanche breakdown.