posted on 2020-03-02, 20:16authored byBo Wang, Sisi Yang, Yu Wang, Ragib Ahsan, Xiaowei He, Younghee Kim, Han Htoon, Rehan Kapadia, Demis D. John, Brian Thibeault, Stephen K. Doorn, Stephen B. Cronin
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. Here we report suppression of
incandescence via Auger recombination 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., Vg1 = −Vg2), we create a pn-junction within the CNT.
Under these gating conditions, we observe a sharp peak in the incandescence
intensity around zero applied gate voltage, where the intrinsic region
has the largest spatial extent. Here, the emission occurs under high
electrical power densities of around 0.1 MW/cm2 (or 6 μW)
and arises from thermal emission at elevated temperatures above 800
K (i.e., incandescence). It is somewhat surprising that this thermal
emission intensity is so sensitive to the gating conditions, and we
observe a 1000-fold suppression of light emission between Vg1 = 0 and 15 V, over a range in which the electrical
power dissipated in the nanotube is roughly constant. This behavior
is understood on the basis of Auger recombination, which suppresses
light emission by the excitation of free carriers. Based on the calculated
carrier density and band profiles, the length of the intrinsic region
drops by a factor of 7–25× over the range from |Vg| = 0 to 15 V. We, therefore, conclude that
the light emission intensity is significantly dependent on the free
carrier density profile and the size of the intrinsic region in these
CNT devices.