Direct probe of excitonic and continuum transitions in the photocurrent spectroscopy of individual carbon nanotube p-n diodes

Abstract

The authors show that a carbon nanotube p-n diode is a very sensitive probe of optical transitions in individual single-walled carbon nanotubes. In the photocurrent spectra, an alternating sequence of resonant peaks from dissociation of excitons and exciton-phonon bound states, for the lowest and higher electronic subbands, is observed. At an intermediate energy, the onset of continuum is observed that allows measurement of exciton binding energies. Both the binding energy and the onset of continuum follow the inverse diameter relation as expected from general theory of optical transitions in nanotubes.

Uncooled Carbon Nanotube Photodetectors

“…[49,66,67] In 2013, Barkelid et al systematically studied the photocurrent generation of SWCNT p-n diodes. [67] Their studies revealed that the photocurrent generation of metallic nanotubes was due to thermal effects, while the photovoltaic effect was responsible for the photocurrent generation in semiconducting nanotubes.…”

“…Later, numerous studies put attention on the spatially-and spectrally-resolved photocurrent of individual CNT devices to explore the electron-hole pair generation and separation in semiconducting SWCNTs [46,47,48,49] and the nanophysics of individual CNT devices such as the formation of Shottky barriers at the CNT-metal electrode interfaces. [50,51,52] Although photoconductors based on individual CNTs are a useful platform to investigate the photophysics of nanodevices, the signal is too weak for practical photodetection due to the small absorption cross section.…”

Single carbon nanotube photovoltaic device

“…For wavelengths of 900 nm and longer a large selection of carbon nanotubes are available with E11 at these wavelengths. The FWHM of the E11 is typically of the order of 50 meV, 17,18 and the density of carbon nanotube chiralities with the E11 above 900 nm is sufficiently high, with respect to the absorption linewidth, to readily cover the infra-red part of the solar spectrum.…”

“…After locating the position of the nanotube diode, we performed photocurrent spectroscopy 4,14,17 to identify the optical transitions in the carbon nanotube. Fig.…”

Applications of carbon materials in photovoltaic solar cells

“…Free electron/ hole pairs excited by photons can be either separated by an externally applied voltage [32], by internal fields at the Schottky barriers [33,34], at p-n junctions [35][36][37] or at defects [38,39]. A photocurrent [32] or a photovoltage [33][34][35][36][37][38][39] can be generated.…”