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Kargar A, Sukrittanon S, Zhou C, Ro YG, Pan X, Dayeh SA, Tu CW, Jin S. GaP/ GaNP Heterojunctions for Efficient Solar-Driven Water Oxidation. Small 2017; 13:1603574. [PMID: 28371293 DOI: 10.1002/smll.201603574] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 01/25/2017] [Indexed: 06/07/2023]
Abstract
The growth and characterization of an n-GaP/i-GaNP/p+ -GaP thin film heterojunction synthesized using a gas-source molecular beam epitaxy (MBE) method, and its application for efficient solar-driven water oxidation is reported. The TiO2 /Ni passivated n-GaP/i-GaNP/p+ -GaP thin film heterojunction provides much higher photoanodic performance in 1 m KOH solution than the TiO2 /Ni-coated n-GaP substrate, leading to much lower onset potential and much higher photocurrent. There is a significant photoanodic potential shift of 764 mV at a photocurrent of 0.34 mA cm-2 , leading to an onset potential of ≈0.4 V versus reversible hydrogen electrode (RHE) at 0.34 mA cm-2 for the heterojunction. The photocurrent at the water oxidation potential (1.23 V vs RHE) is 1.46 and 7.26 mA cm-2 for the coated n-GaP and n-GaP/i-GaNP/p+ -GaP photoanodes, respectively. The passivated heterojunction offers a maximum applied bias photon-to-current efficiency (ABPE) of 1.9% while the ABPE of the coated n-GaP sample is almost zero. Furthermore, the coated n-GaP/i-GaNP/p+ -GaP heterojunction photoanode provides a broad absorption spectrum up to ≈620 nm with incident photon-to-current efficiencies (IPCEs) of over 40% from ≈400 to ≈560 nm. The high low-bias performance and broad absorption of the wide-bandgap GaP/GaNP heterojunctions render them as a promising photoanode material for tandem photoelectrochemical (PEC) cells to carry out overall solar water splitting.
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Affiliation(s)
- Alireza Kargar
- Department of Electrical and Computer Engineering, University of California-San Diego, La Jolla, CA, 92093, USA
| | - Supanee Sukrittanon
- Materials Science and Engineering Program, University of California-San Diego, La Jolla, CA, 92093, USA
| | - Chang Zhou
- School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, Heilongjiang, 150001, P. R. China
- Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Yun Goo Ro
- Department of Electrical and Computer Engineering, University of California-San Diego, La Jolla, CA, 92093, USA
| | - Xiaoqing Pan
- Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, 48109, USA
- Department of Chemical Engineering and Materials Science, University of California-Irvine, Irvine, CA, 92697, USA
- Department of Physics and Astronomy, University of California-Irvine, Irvine, CA, 92697, USA
| | - Shadi A Dayeh
- Department of Electrical and Computer Engineering, University of California-San Diego, La Jolla, CA, 92093, USA
- Materials Science and Engineering Program, University of California-San Diego, La Jolla, CA, 92093, USA
| | - Charles W Tu
- Department of Electrical and Computer Engineering, University of California-San Diego, La Jolla, CA, 92093, USA
- Materials Science and Engineering Program, University of California-San Diego, La Jolla, CA, 92093, USA
| | - Sungho Jin
- Materials Science and Engineering Program, University of California-San Diego, La Jolla, CA, 92093, USA
- Department of Mechanical and Aerospace Engineering, University of California-San Diego, La Jolla, CA, 92093, USA
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Dobrovolsky A, Stehr JE, Sukrittanon S, Kuang Y, Tu CW, Chen WM, Buyanova IA. Fabry-Perot Microcavity Modes in Single GaP/ GaNP Core/Shell Nanowires. Small 2015; 11:6331-6337. [PMID: 26505738 DOI: 10.1002/smll.201501538] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Revised: 07/15/2015] [Indexed: 06/05/2023]
Abstract
Semiconductor nanowires (NWs) are attracting increasing interest as nanobuilding blocks for optoelectronics and photonics. A novel material system that is highly suitable for these applications are GaNP NWs. In this article, we show that individual GaP/GaNP core/shell nanowires (NWs) grown by molecular beam epitaxy on Si substrates can act as Fabry-Perot (FP) microcavities. This conclusion is based on results of microphotoluminescence (μ-PL) measurements performed on individual NWs, which reveal periodic undulations of the PL intensity that follow an expected pattern of FP cavity modes. The cavity is concluded to be formed along the NW axis with the end facets acting as reflecting mirrors. The formation of the FP modes is shown to be facilitated by an increasing index contrast with the surrounding media. Spectral dependence of the group refractive index is also determined for the studied NWs. The observation of the FP microcavity modes in the GaP/GaNP core/shell NWs can be considered as a first step toward achieving lasing in this quasidirect bandgap semiconductor in the NW geometry.
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Affiliation(s)
- Alexander Dobrovolsky
- Department of Physics, Chemistry and Biology, Linköping University, 581 83, Linköping, Sweden
| | - Jan E Stehr
- Department of Physics, Chemistry and Biology, Linköping University, 581 83, Linköping, Sweden
| | - Supanee Sukrittanon
- Graduate Program of Materials Science and Engineering, La Jolla, CA, 92093, USA
| | - Yanjin Kuang
- Department of Physics, University of California, La Jolla, CA, 92093, USA
| | - Charles W Tu
- Department of Electrical and Computer Engineering, University of California, La Jolla, CA, 92093, USA
| | - Weimin M Chen
- Department of Physics, Chemistry and Biology, Linköping University, 581 83, Linköping, Sweden
| | - Irina A Buyanova
- Department of Physics, Chemistry and Biology, Linköping University, 581 83, Linköping, Sweden
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Dobrovolsky A, Persson POÅ, Sukrittanon S, Kuang Y, Tu CW, Chen WM, Buyanova IA. Effects of Polytypism on Optical Properties and Band Structure of Individual Ga(N)P Nanowires from Correlative Spatially Resolved Structural and Optical Studies. Nano Lett 2015; 15:4052-4058. [PMID: 25988267 DOI: 10.1021/acs.nanolett.5b01054] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
III-V semiconductor nanowires (NWs) have gained significant interest as building blocks in novel nanoscale devices. The one-dimensional (1D) nanostructure architecture allows one to extend band structure engineering beyond quantum confinement effects by utilizing formation of different crystal phases that are thermodynamically unfavorable in bulk materials. It is therefore of crucial importance to understand the influence of variations in the NWs crystal structure on their fundamental physical properties. In this work we investigate effects of structural polytypism on the optical properties of gallium phosphide and GaP/GaNP core/shell NW structures by a correlative investigation on the structural and optical properties of individual NWs. The former is monitored by transmission electron microscopy, whereas the latter is studied via cathodoluminescence (CL) mapping. It is found that structural defects, such as rotational twins in zinc blende (ZB) GaNP, have detrimental effects on light emission intensity at low temperatures by promoting nonradiative recombination processes. On the other hand, formation of the wurtzite (WZ) phase does not notably affect the CL intensity neither in GaP nor in the GaNP alloy. This suggests that zone folding in WZ GaP does not enhance its radiative efficiency, consistent with theoretical predictions. We also show that the change in the lattice structure have negligible effects on the bandgap energies of the GaNP alloys, at least within the range of the investigated nitrogen compositions of <2%. Both WZ and ZB GaNP are found to have a significantly higher efficiency of radiative recombination as compared with that in parental GaP, promising for potential applications of GaNP NWs as efficient nanoscale light emitters within the desirable amber-red spectral range.
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Affiliation(s)
- Alexander Dobrovolsky
- †Department of Physics, Chemistry and Biology, Linköping University, S-581 83 Linköping, Sweden
| | - Per O Å Persson
- †Department of Physics, Chemistry and Biology, Linköping University, S-581 83 Linköping, Sweden
| | | | | | | | - Weimin M Chen
- †Department of Physics, Chemistry and Biology, Linköping University, S-581 83 Linköping, Sweden
| | - Irina A Buyanova
- †Department of Physics, Chemistry and Biology, Linköping University, S-581 83 Linköping, Sweden
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Stehr JE, Dobrovolsky A, Sukrittanon S, Kuang Y, Tu CW, Chen WM, Buyanova IA. Optimizing GaNP coaxial nanowires for efficient light emission by controlling formation of surface and interfacial defects. Nano Lett 2015; 15:242-247. [PMID: 25426571 DOI: 10.1021/nl503454s] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report on identification and control of important nonradiative recombination centers in GaNP coaxial nanowires (NWs) grown on Si substrates in an effort to significantly increase light emitting efficiency of these novel nanostructures promising for a wide variety of optoelectronic and photonic applications. A point defect complex, labeled as DD1 and consisting of a P atom with a neighboring partner aligned along a crystallographic ⟨ 111 ⟩ axis, is identified by optically detected magnetic resonance as a dominant nonradiative recombination center that resides mainly on the surface of the NWs and partly at the heterointerfaces. The formation of DD1 is found to be promoted by the presence of nitrogen and can be suppressed by reducing the strain between the core and shell layers, as well as by protecting the optically active shell by an outer passivating shell. Growth modes employed during the NW growth are shown to play a role. On the basis of these results, we identify the GaP/GaN(y)P(1-y)/GaN(x)P(1-x) (x < y) core/shell/shell NW structure, where the GaN(y)P(1-y) inner shell with the highest nitrogen content serves as an active light-emitting layer, as the optimized and promising design for efficient light emitters based on GaNP NWs.
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Affiliation(s)
- Jan E Stehr
- Department of Physics, Chemistry and Biology, Linköping University , 581 83 Linköping, Sweden
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