Near-field scanning photocurrent microscopy of a nanowire photodetector

Abstract

A near-field scanning optical microscope was used to image the photocurrent induced by local illumination along the length of a metal-semiconductor-metal ͑MSM͒ photodetector made from an individual CdS nanowire. Nanowire MSM photodetectors exhibited photocurrents ϳ10 5 larger than the dark current ͑Ͻ2 pA͒ under uniform monochromatic illumination; under local illumination, the photoresponse was localized to the near-contact regions. Analysis of the spatial variation and bias dependence of the local photocurrent allowed the mechanisms of photocarrier transport and collection to be identified, highlighting the importance of near-field scanning photocurrent microscopy to elucidating the operating principles of nanowire devices.

Temperature dependent photoluminescence of single CdS nanowires

“…growth technique 1 have resulted in the development of nanoscale optical devices including nanowire-based photodetectors, 2 waveguides, 3 and lasers. 4,5 Understanding the nature of nanowire defects and how to control them is particularly important for the future development of nanowire-based structures and devices.…”

Imaging Ultrafast Carrier Transport in Nanoscale Field-Effect Transistors

“…The carrier diffusion motions induced by a pump pulse located in the middle of the NWs were visualized; however, these optical measurements are limited for interrogating the carrier dynamics in operating devices because they strongly depend on the non-linear properties of materials and they are frequently obscured by the substrate signals. Consequently, these techniques are not ideal for low-dimensional systems with NWs thinner than the optical spot size (<100 nm) or with SWNTs.Scanning photocurrent microscopy (SPCM) techniques have been introduced as powerful tools for investigating local optoelectronic characteristics, such as metallic contacts, defects, interfaces, and junctions [12][13][14][15][16][17][18][19] . We were able to collect localized electronic band information that is not disturbed by signals originating from the substrate, and hence, compared with conventional optical pump-probe techniques, SPCM can provide a higher signal-to-noise ratio.…”

“…Scanning photocurrent microscopy (SPCM) techniques have been introduced as powerful tools for investigating local optoelectronic characteristics, such as metallic contacts, defects, interfaces, and junctions [12][13][14][15][16][17][18][19] . We were able to collect localized electronic band information that is not disturbed by signals originating from the substrate, and hence, compared with conventional optical pump-probe techniques, SPCM can provide a higher signal-to-noise ratio.…”

Imaging of the Schottky Barriers and Charge Depletion in Carbon Nanotube Transistors

“…We find that in our one-dimensional CNTFETs, this is the case over a substantial gate-voltage range that includes the transistor "off"-state and the threshold voltage for electron conduction, consistent with theoretical predictions of an extremely slowly decaying potential tail at interfaces in one dimension. 3 In the future, we plan to perform measurements on CNTs with near-field excitation to probe the potential profile in the near-field region of the contact, 23 where the band bending could have a different functional form.…”