Avalanche Photoemission in Suspended Carbon Nanotubes: Light Without Heat

We observe bright electroluminescence from suspended carbon nanotube (CNT) field effect transistors (FETs) under extremely low applied electrical powers (~nW). Here, light emission occurs under positive applied gate voltages, with the FET in its "off" state. This enables us to apply high bias voltages (4V) without heating the CNT. Under these conditions, we observe light emission at currents as small as 1nA, which is three orders of magnitude lower than previous studies. The mechanism of light emission is understood on the basis of steep band bending that occurs in the conduction and valence band profiles at the contacts, which produces a peak electric field of 500kV/cm, enabling the acceleration of carriers beyond the threshold of exciton emission. The exciton-generated electrons and holes are then accelerated and emit excitons in an avalanche process. We also observe light emission at negative applied gate voltages in its "on" state. However, substantial Joule heating (T>1000K) is also observed so that it is difficult to separate the mechanisms of thermal emission from hot carrier photoemission in this regime.