There are various mechanisms of light emission in carbon nanotubes (CNTs), which give rise to a wide range of spectral characteristics that provide important information regarding the underlying physical processes of photon emission. Here, we report resonant electroluminescence in suspended carbon nanotube pn-junctions generated from dual gate CNT field effect transistor (FET) devices. By applying equal and opposite voltages to the gate electrodes (i.e., V_(g1) = -V_(g2)), we create a pn-junction within the CNT. Under these gating conditions, we observe a sharp resonance in the electroluminescence intensity around zero applied gate voltages, where the depletion region in the p-i-n device has the largest spatial extent. Here, the emission occurs under high electrical power densities around 0.1 MW/cm~2 (or 6μW) and arises from thermal emission at elevated temperatures above 1000K. It is somewhat surprising that this thermal emission intensity is so sensitive to the gating conditions, and we observe a resonant enhancement factor of 1000-fold between V_(g1)=0V and V_(g1)=15V, over a range in which the electrical power dissipated in the nanotube is roughly constant. This resonant behavior is understood on the basis of two phenomena that occur when the depletion region is aligned with the trench across which the nanotube is suspended: 1.) heating is increased in the suspended region because the nanotube is not directly heat sunk to the underlying substrate and 2.) light emission is enhanced in the suspended region due to reduced non-radiative recombination caused by the underlying substrate. Based on the calculated conduction and valence band profiles in the device, we find that the size of the depletion region drops by a factor of 5-1 OX over the range from |V_g|=0V to 15V. We, therefore, conclude that the light emission intensity is significantly dependent on the length of the depletion region in these CNT devices.
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