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Nanowire-based Infrared Photodetectors
Halmstad University, School of Information Technology, Halmstad Embedded and Intelligent Systems Research (EIS), MPE-lab. (Nanovetenskap)
2015 (English)Conference paper, Abstract (Refereed)
Abstract [en]

In this talk, I will discuss electrical and optical properties of infrared photodetectors/solar cells based on  square millimeter ensembles (> 1 million) of vertically processed InP/InAsP semiconductor nanowires grown on InP substrates.

To investigate current generation processes in InP p+-i-n photodetectors/solar cells, we fabricated a sample series where the p+-segment length was varied, as well as optimized solar cells with 9.3 % efficiency with similar design. The electrical data generally display excellent rectifying behavior with small leakage currents. From spectrally resolved photocurrent measurements, we conclude that the photocurrent generation process depends strongly on the p+-segment length. Without p+-segment, photogenerated carriers funneled from the substrate into the NWs contribute significantly to the photocurrent. Adding a p+-segment decouples the substrate and shifts the depletion region, and collection of photogenerated carriers, to the nanowires, in agreement with sophisticated theoretical modeling. In optimized solar cells, clear spectral signatures of interband transitions in the ZB and WZ InP layers of the mixed-phase i-segments are observed. Complementary measurements of the dependence of the photocurrent on angle of incidence and polarization, as well as electroluminescence, support our interpretations.

I will also discuss large area photoconductors based on n-i-n InP nanowires with axial InAsP quantum wells embedded in the i-region. Spectrally resolved photocurrent measurements and photoluminescence measurements reveal clear interband transitions both in the InP segments and InAsP quantum wells. By increasing the number of incorporated quantum wells, one important goal is to enhance the contribution from intersubband transitions in the quantum wells thereby facilitating detectors/focal plane arrays with a broad detection window from near-infrared to long-wavelength infrared regions.

Finally, I will briefly mention efforts targeting large area p+-n-n-  InP/InAsP avalanche nanowire photodiodes with low electric field in the low-bandgap InAsP segment and high electric field in the InP multiplication region. Besides clear interband photocurrent signals from the InP and InAsP regions, a strong bias-dependent blueshifted photocurrent peak appears at forward bias offering an interesting novel tunability of the spectral window.

The presented nanowire-based photodetectors can potentially be grown on silicon substrates due to the small footprint of the nanowires. Successfully developed, novel detector families of low-cost, high performance broadband detectors for optical communication, thermal imaging and solar cell applications can thus be realized.

Place, publisher, year, edition, pages
2015.
Keyword [en]
Photodetectors, solar cells, nanowires
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:hh:diva-27520OAI: oai:DiVA.org:hh-27520DiVA: diva2:781799
Conference
EMN Meeting on Photovoltaics 2015, Orlando, Florida, USA, January 12-15, 2015
Available from: 2015-01-19 Created: 2015-01-19 Last updated: 2015-03-30Bibliographically approved

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