| 1. |
- Berg, Alexander, et al.
(författare)
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Radial Nanowire Light-Emitting Diodes in the (AlxGa1-x)yIn1-yP Material System
- 2016
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Ingår i: Nano letters (Print). - Washington, DC : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 16:1, s. 656-662
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Tidskriftsartikel (refereegranskat)abstract
- Nanowires have the potential to play an important role for next-generation light-emitting diodes. In this work, we present a growth scheme for radial nanowire quantum-well structures in the AlGaInP material system using a GaInP nanowire core as a template for radial growth with GaInP as the active layer for emission and AlGaInP as charge carrier barriers. The different layers were analyzed by X-ray diffraction to ensure lattice-matched radial structures. Furthermore, we evaluated the material composition and heterojunction interface sharpness by scanning transmission electron microscopy energy dispersive X-ray spectroscopy. The electro-optical properties were investigated by injection luminescence measurements. The presented results can be a valuable track toward radial nanowire light-emitting diodes in the AlGaInP material system in the red/orange/yellow color spectrum. © 2015 American Chemical Society.
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| 2. |
- Jafari Jam, Reza, et al.
(författare)
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III-V nanowire synthesis by use of electrodeposited gold particles
- 2015
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Ingår i: Nano letters (Print). - Washington, DC : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 15:1, s. 134-138
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires are great candidates for building novel electronic devices. Considering the cost of fabricating such devices, substrate reuse and gold consumption are the main concerns. Here we report on implementation of high throughput gold electrodeposition for selective deposition of metal seed particles in arrays defined by lithography for nanowire synthesis. By use of this method, a reduction in gold consumption by a factor of at least 300 was achieved, as compared to conventional thermal evaporation for the same pattern. Because this method also facilitates substrate reuse, a significantly reduced cost of the final device is expected. We investigate the morphology, crystallography, and optical properties of InP and GaAs nanowires grown from electrodeposited gold seed particles and compare them with the properties of nanowires grown from seed particles defined by thermal evaporation of gold. We find that nanowire synthesis, as well as the material properties of the grown nanowires are comparable and quite independent of the gold deposition technique. On the basis of these results, electrodeposition is proposed as a key technology for large-scale fabrication of nanowire-based devices.
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| 3. |
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| 4. |
- Jain, Vishal, 1989-, et al.
(författare)
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A comparative study of nanowire based infrared p+-i-n+ photodetectors
- 2012
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Konferensbidrag (refereegranskat)abstract
- We present a comparative study of electrical and optical properties of two types of p+-i-n+ photodetectors based on self-assembled ensembles of vertical InP nanowires (NWs) monolithically grown on InP. The detectors differ in the type of p+ contact, one detector geometry has p+-i-n+ segments integrated into the NWs (type A) while the other detector has i-n+ NW segments grown directly on a p+ substrate(type B). The samples were prepared by first depositing 80 nm Au nanoparticles on a p+ InP substrate using an aerosol technique and subsequently growing NWs using MOVPE. The NWs have a polytypecrystal structure of alternating wurtzite and zincblende segments. The processing of the detectors include deposition of SiO2, followed by an etching step to remove the oxide from the tip of the NWs, and finally sputtering of ITO on 1x1 mm2 device areas. The two most prominent differences between the detectors concern the current-voltage (I-V) characteristics and the spatial location of generated photocurrent. From spectrally resolved photocurrent measurements, we conclude that the photocurrent in detector type A is primarily generated in the NWs, whereas the photocurrent in type B detectors mainly stems from the substrate. Photogenerated carriers in the substrate diffuse to the NWs where they are effectively funnelled into the NWs. The I-V characteristics of the type A detector displays a non-trivial transport behaviour for forward biases, whereas type B shows excellent rectifying behavior with an ideality factor of about 2.5. We will discuss detailed analysis of the spectral fingerprints of the two detector types revealing the mixed crystal phase of the polytype NWs and bandstructure effects, temperature dependence of the I-V characteristics and typical photodetector parameters.
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| 5. |
- Jain, Vishal, 1989-, et al.
(författare)
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Large Area Photodetectors at 1.3/1.55 μm Based on InP/InAsP NWs
- 2014
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Konferensbidrag (refereegranskat)abstract
- Optical communication systems benefit a lot from APDs due to their increased photocurrent gain as compared to conventional photodetectors. An avalanche region in a high bandgap material is especially useful to avoid the tunneling leakage currents in smaller bandgap materials needed for absorption at 1.3/1.55 µm wavelengths. Self-assembled III-V semiconductor nanowires have a key advantage owing to the enhanced absorption due to optical resonance effects and the strain relaxation in NWs, thus facilitating monolithic integration of different heterostructures on cheaper substrates. Here, we present electrical and optical results from large ensembles of InP/InAsP NWs, axially grown on p+ InP substrates. The NW base consists of an InP p-n junction acting as the avalanche region followed by an InP/InAsP absorption region, and ending with a top InP n+-segment. The 130nm diameter NW arrays are contacted in a vertical geometry using SiO2 as the insulating layer and ITO as the top contact. The n-doping in the avalanche region is varied to study it’s influence on the avalanche mechanism. Also the bandgap in the absorption region is varied from pure InP to smaller bandgap InAsP by varying the As content. Clear interband signals from different crystal phases of InP/InAsP are observed in photocurrent spectroscopy. Moreover, the photocurrent spectra are consistent with spatially resolved photoluminescence signals. We also report on polarization and angle dependent photocurrent response of the NW array.
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| 6. |
- Jain, Vishal, 1989-, et al.
(författare)
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Large area photodetectors based on InP NWs with InAs/InAsP QWs
- 2014
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Konferensbidrag (refereegranskat)abstract
- Focal plane arrays have a widespread use in infrared imaging, which often rely on cryogenic cooling to curtail the dark current level necessary for a reasonable signal-to-noise ratio. Quantum well (QW) infrared photodetectors are uniform over large areas, but suffer from a severe drawback related to the selection rules for intersubband absorption. An interesting alternative is self-assembled III-V nanowires offering a key advantage owing to the enhanced absorption by optical resonance effects and strain relaxation.We present electrical and optical results from large ensembles of n+-i-n+ InP NWs, axially grown on InP substrates with InAs/InAsP QWs embedded within the i-segment, designed for both interband and intersubband detection. The NWs are contacted in a vertical geometry using 50 nm SiO2 as the insulating layer and ITO as the top contact. We first investigate the crystal quality of the InAsP QWs grown in 180 nm diameter NWs, using PL, CL and TEM. To achieve more abrupt InAs/InAsP QWs, we grow 130 nm diameter NWs and deplete the In present in the Au catalysts. The effect of n-doping on the device performance is studied by fabricating two different NW geometries, with and without an n+-segment grown before the nominal i-segment in the NW. In addition, the position of the QWs within the i-segment is varied to further scrutinize effects related to doping and crystal structure. Finally, we report spectrally resolved photocurrent results from the QWs in the near-infrared region and discuss about the further developments needed for intersubband detection.
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| 7. |
- Jain, Vishal, 1989-, et al.
(författare)
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Processing and Characterization of Nanowire Arrays for Photodetectors
- 2015
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Ingår i: Nano-Structures for Optics and Photonics. - Dordrecht : Springer. - 9789401791427 - 9789401791328 - 9789401791335 ; , s. 511-512
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Konferensbidrag (refereegranskat)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 (Må 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 (Borgström 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 × 1 mm2 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 p +-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). © Springer Science+Business Media Dordrecht 2015.
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| 8. |
- Karimi, Mohammad, 1988-, et al.
(författare)
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Intersubband Quantum Disc-in-Nanowire Photodetectors with Normal-Incidence Response in the Long-Wavelength Infrared
- 2018
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Ingår i: Nano letters (Print). - Washington : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:1, s. 365-372
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires have great potential for realizing broadband photodetectors monolithically integrated with silicon. However, the spectral range of such detectors has so far been limited to selected regions in the ultraviolet, visible, and near-infrared regions. Here, we report on the first intersubband nanowire heterostructure array photodetectors exhibiting a spectrally resolved photoresponse from the visible to long-wavelength infrared. In particular, the infrared response from 3 to 20 μm is enabled by intersubband transitions in low-bandgap InAsP quantum discs synthesized axially within InP nanowires. The intriguing optical characteristics, including unexpected sensitivity to normal incident radiation, are explained by excitation of the longitudinal component of optical modes in the photonic crystal formed by the nanostructured portion of the detectors. Our results provide a generalizable insight into how broadband nanowire photodetectors may be designed and how engineered nanowire heterostructures open up new, fascinating opportunities for optoelectronics.
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| 9. |
- Karimi, Mohammad, 1988-, et al.
(författare)
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Nanowire photodetectors with embedded quantum heterostructures for infrared detection
- 2019
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Ingår i: Infrared physics & technology. - Amsterdam : Elsevier. - 1350-4495 .- 1879-0275. ; 96, s. 209-212
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Tidskriftsartikel (refereegranskat)abstract
- Nanowires offer remarkable opportunities for realizing new optoelectronic devices because of their unique fundamental properties. The ability to engineer nanowire heterostructures with large bandgap variations is particularly interesting for technologically important broadband photodetector applications. Here we report on infrared photodetectors based on arrays of InP nanowires with embedded InAsP quantum discs. We demonstrate a strongly reduced dark current in the detector elements by compensating the unintentional n-doping in the nominal intrinsic region of the InP nanowires by in-situ doping with Zn, a crucial step towards realizing high-performance devices. The optimized array detectors show a broad spectral sensitivity at normal incidence for wavelengths from visible to far-infrared up to 20 μm, promoted by both interband and intersubband transitions. Optical simulations show that the unexpected normal incidence response at long wavelengths is due to non-zero longitudinal modes hosted by the nanowires. © 2018 Elsevier B.V.
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| 10. |
- Karimi, Mohammad, 1988-, et al.
(författare)
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Room-temperature InP/InAsP Quantum Discs-in-Nanowire Infrared Photodetectors
- 2017
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Ingår i: Nano letters (Print). - Washington, DC : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 17:6, s. 3356-3362
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Tidskriftsartikel (refereegranskat)abstract
- The possibility to engineer nanowire heterostructures with large bandgap variations is particularly interesting for technologically important broadband photodetector applications. Here we report on a combined study of design, fabrication, and optoelectronic properties of infrared photodetectors comprising four million n+–i–n+ InP nanowires periodically ordered in arrays. The nanowires were grown by metal–organic vapor phase epitaxy on InP substrates, with either a single or 20 InAsP quantum discs embedded in the i-segment. By Zn compensation of the residual n-dopants in the i-segment, the room-temperature dark current is strongly suppressed to a level of pA/NW at 1 V bias. The low dark current is manifested in the spectrally resolved photocurrent measurements, which reveal strong photocurrent contributions from the InAsP quantum discs at room temperature with a threshold wavelength of about 2.0 μm and a bias-tunable responsivity reaching 7 A/W@1.38 μm at 2 V bias. Two different processing schemes were implemented to study the effects of radial self-gating in the nanowires induced by the nanowire/SiOx/ITO wrap-gate geometry. Summarized, our results show that properly designed axial InP/InAsP nanowire heterostructures are promising candidates for broadband photodetectors. © 2017 American Chemical Society.
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