Optoelectronics with Carbon Nanotubes

In this chapter, we report on the realization of a light emitting p-i-n diode from a highly
aligned film of semiconducting carbon nanotubes that emits light in the near-infrared spectral
range. A split gate design similar to the single-tube CNT diode allows for tuning both the
rectifying electrical behavior of the diode and its light generation efficiency. The CNT film
diode produces light that is polarized along the device channel, a direct consequence of the high
degree of CNT alignment in the film that reflects the polarization property of the 1D nature of
individual tubes.
2. Physical characteristics of CNT films and top-gated devices
We deposited CNT thin films on a Si(p++)/SiO2(100nm) substrate from a suspension of
99% semiconducing (arc discharge) carbon nanotubes with diameters ranging from 1.3 to 1.7
nm, separated by density-gradient ultracentrifugation 98 . With this desposition technique, CNTs
align in parallel at the contact line between the solution and a vertically immersed planar
substrate. The slip-stick motion of the contact line during evaporation produces periodic arrays
of regular CNT thin film stripes that cover a large area of the substrate, each stripe having a
width of about 10 μm and a height of 1 to 8 nm, depending on the degree of CNT bundling (see
Figure V-1 (c)). The CNT stripe formation relies solely on self organization without the need for
etching or lithography to obtain the patterns. These CNT films have been extensively
characterized by optical and electrical techniques as well as by SEM and AFM (see Ref. 99 and
Figure V-1). Further details on the assembly technique and its mechanism are available in Ref.
99.
We first contacted sections of a stripe by source and drain electrodes (Ti = 1 nm/Pd = 40
nm/Au = 20 nm, Figure V-1 (a) ), and then deposited 30 to 50 nm of Al2O3 by means of atomic
layer deposition. Ti top gates (thickness: 15 to 35 nm) were then defined by e-beam lithography
and deposited by e-beam evaporation (Figure V-1 (b) and V-2 (a)).
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