A SEM-EBIC minority-carrier diffusion-length measurement technique

Ioannou, D.E.; Dimitriadis, C. A.

doi:10.1109/t-ed.1982.20721

Cited by 124 publications

(50 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The net photocurrent owing to these carriers is dominated by the edge closest to the point of illumination. This physical picture is analogous to the microscopy of photo-and electron-beam-induced current in semiconductor devices 24,25 , where the net induced current reflects the transport of minority carriers. In the present case, both hot electrons and hot holes simultaneously act as 'minority' carriers.…”

mentioning

confidence: 93%

Visualization of charge transport through Landau levels in graphene

Nazin

Zhang

et al. 2010

Nature Phys

View full text Add to dashboard Cite

Band bending and the associated spatially inhomogeneous population of Landau levels play a central role in the physics of the quantum Hall effect (QHE) by constraining the pathways for charge-carrier transport and scattering 1 . Recent progress in understanding such effects in low-dimensional carrier gases in conventional semiconductors has been achieved by realspace mapping using local probes 2,3 . Here, we use spatially resolved photocurrent measurements in the QHE regime to study the correlation between the distribution of Landau levels and the macroscopic transport characteristics in graphene. Spatial maps show that the net photocurrent is determined by hot carriers transported to the periphery of the graphene channel, where QHE edge states provide efficient pathways for their extraction to the contacts. The photocurrent is sensitive to the local filling factor, which allows us to reconstruct the local charge density in the entire conducting channel of a graphene device.Since the demonstration of the unusual half-integer QHE in graphene 4,5 , many related QHE experiments have been interpreted within the framework of edge-state transport [6][7][8] , that is, the backscattering-free flow of charge through edge states 9 bounded by insulating barriers with incompressible electron densities 10 . Although compressible and incompressible electron densities have recently been observed in graphene 11 , their role in shaping the QHE in graphene remains to be explained. Spatially inhomogeneous charge distributions owing to adsorbate-induced surface doping 12 are expected to be particularly pronounced in graphene and could cause deviations from pure edge-state transport. Here, we use scanning photocurrent microscopy to explore these effects by mapping carrier propagation through graphene Landau levels in the QHE regime.The experiments were carried out on two-terminal monolayer graphene field-effect devices at 4.2 K and in magnetic fields B up to ±9 T (Fig. 1a,b). In these conditions, the conductance of our devices (Fig. 1c) shows series of local extrema 6,8,11,13,14 associated with individual Landau levels 13,15 , with maxima predicted to occur at quantized Hall conductances of 2, 4, 6, 10 and 14 e 2 /h (refs 13,15). The observed maxima are higher owing to an inhomogeneous filling-factor distribution across the device, as shown below.Photocurrent maps were obtained by scanning a focused laser across the graphene channel, and recording the two-terminal photocurrent signal as a function of beam position. Previously, a similar approach has been used to investigate contact-induced band bending [16][17][18][19] and the photo-thermoelectric effect 20 in graphene at B = 0, as well as the electrostatics of the QHE in conventional semiconductor devices [21][22][23] . We observe that the gate-voltagedependent photocurrent at fixed locations is oscillatory, with polarity determined by the direction of the magnetic field (Fig. 1d). Such local oscillations are due to a recurring global photocurrent distribution across the device, sy...

show abstract