Extracting the Energy Sensitivity of Charge Carrier Transport and Scattering

Abstract

It is a challenge to extract the energy sensitivity of charge carriers’ transport and scattering from experimental data, although a theoretical estimation in which the existing scattering mechanism(s) are preliminarily assumed can be easily done. To tackle this problem, we have developed a method to experimentally determine the energy sensitivities, which can then serve as an important statistical measurement to further understand the collective behaviors of multi-carrier transport systems. This method is validated using a graphene system at different temperatures. Further, we demonstrate the application of this method to other two-dimensional (2D) materials as a guide for future experimental work on the optimization of materials performance for electronic components, Peltier coolers, thermoelectricity generators, thermocouples, thermopiles, electrical converters and other conductivity and/or Seebeck-effect-related sensors.

Inferring the energy sensitivity and band gap of electronic transport in a network of carbon nanotubes

“…Therefore, we can speculate that ballistic scattering inside the single carbon nanotubes is the dominant mechanism at this temperature inside this sample. The asymmetry of transport between holes and electrons (γ) is inferred to be 1.75, which is similar to the value of 1.50 observed in graphene samples at the same temperature 41 , 42 .…”

“…The pinpointed maximum points in the Seebeck coefficient curve also infer that the energy sensitivities of carrier transport are s e = 1.08 for electrons and s h = 1.10 for holes. At 300 K, electrons in graphene will be scattered strongly by long-range disorders such as thermal ripples 56 , which results in a value of energy sensitivities ( s e and s h ) notably greater than 1.00 41 , 42 . This does not happen here in the carbon nanotube network.…”

“…Different transport channels with one or more scattering mechanisms have their own energy sensitivities 43 , 44 . When multiple channels of transport exist, this energy sensitivity reflects the statistical behavior of the carriers transported within the material system 41 .…”

“…Researchers have estimated the average scattering time of carriers by fitting the measured electrical conductivity ( σ ) to a constant relaxation time model 45 or by observing ultrafast laser-assisted photon-electron interactions 46 . However, there was no well-defined method to extract the value of carrier transport or scattering energy sensitivity from transport measurements until Tang pointed out that the highest achievable Seebeck coefficient could be used to infer this quantity 41 . The Seebeck coefficient characterizes the average entropy carried by each single electron or hole in the semiconducting system microscopically and appears to be the voltage generated per unit temperature gradient in the thermoelectricity production process 47 .…”

“…We have discovered that the Seebeck coefficient, a less frequently used transport quantity, can be used to extract a set of electronic features depicting the statistical details of electron and hole transport in a material system, with diffusive, ballistic and/or quantum tunneling transport mechanism(s) 41 . The effective band gap, electron–hole asymmetry, and energy sensitivity to carrier scattering/transport can all be inferred 42 .…”