Processing and characterization of nanowire arrays for photodetectors

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Abstract

We present a fabrication scheme of contacting arrays of vertically standing nanowires (NW) for LEDs (Duan et al. Nature 409:66–69, 2001), photodetectors (Wang et al. Science (NY) 293:1455–1457, 2001) or solar cell applications (Wallentin et al. Science (NY) 339:1057–1060, 2013). Samples were prepared by depositing Au films using nano-imprint lithography (Ma rtensson et al. Nano Lett 4:699–702, 2004) which are used as catalysts for NW growth in a low-pressure metal organic vapour phase epitaxy system where III-V precursors and dopant gases are flown at elevated temperatures which lead to the formation of NWs with different segments (Borgstrom et al. Nano Res 3:264–270, 2010). An insulating SiO2 layer is then deposited and etched from the top segments of the NWs followed by sputtering of a transparent top conducting oxide and opening up 1 1mm2 device areas through a UV lithography step and etching of the top contact from non-device areas. A second UV lithography step was subsequently carried out to open up smaller windows on the ITO squares for bond pad definition, followed by metallization and lift-off; and the substrate is used as back contact. We also report on the electrical and optical properties of near-infrared p+-i-n+photodetectors/solar cells based on square millimeter ensembles of InP nanowires grown on InP substrates. The study includes a sample series where the p+-segment length was varied between 0 and 250 nm, as well as solar cell samples with 9.3% efficiency with similar design. The NWs have a complex modulated crystal structure of alternating wurtzite and zincblende segments, a polytypism that depends on dopant type. The electrical data for all samples display excellent rectifying behavior with an ideality factor of about 2 at 300 K. From spectrally resolved photocurrent measurements, we conclude that the photocurrent generation process depends strongly on the p+- segment length.Without p+-segment in the NWs, photogenerated carriers funneled from the substrate into the NWs contribute significantly to the photocurrent. Adding a pC-segment shifts the depletion region up into the i -region of the NWs reducing the substrate contribution to photocurrent while strongly improving the collections of carriers generated in the NWs, in agreement with theoretical modeling (Fig. 48.1).

Detaljer

Författare
Enheter & grupper
Externa organisationer
  • Halmstad University
  • Harvard University
  • Sol Voltaics AB
Forskningsområden

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Nanoteknik

Nyckelord

Originalspråkengelska
Titel på värdpublikationNano-Structures for Optics and Photonics
Undertitel på gästpublikationOptical Strategies for Enhancing Sensing, Imaging, Communication and Energy Conversion
FörlagSpringer Netherlands
Sidor511-512
Antal sidor2
ISBN (elektroniskt)9789401791335
ISBN (tryckt)9789401791328
StatusPublished - 2015 jan 1
PublikationskategoriForskning
Peer review utfördJa