Conformal GaP layers on Si wire arrays for solar energy applications

Tamboli, Adele C.; Malhotra, Manav; Kimball, Gregory M.; Turner-Evans, Daniel B.; Atwater, Harry A.

doi:10.1063/1.3522895

Cited by 14 publications

(14 citation statements)

References 17 publications

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“…The GaP films coated the Si substrates conformally but exhibited significant surface roughness ( Figure ). The surface roughness resulted from defects that were produced during polar on non‐polar heteroepitaxy, as opposed to indicating polycrystalline growth 19. The thickness of the GaP layer on planar Si substrates was ∼5 μm, as determined by cross‐sectional scanning electron microscopy (SEM).…”

Section: Resultsmentioning

confidence: 99%

“…Si and GaP are nearly lattice matched (fractional lattice mismatch = 0.358%). High quality GaP can therefore be grown heteroepitaxially on Si, as has been reported using liquid phase epitaxy,20 metal organic chemical vapor deposition (MOCVD),19, 21–23 chemical beam epitaxy,24, 25 and halide transport 26, 27. Heteroepitaxial growth strategies therefore can provide a route to planar and structured monolithic tandem photovoltaics and photoelectrochemical cells 28…”

Section: Introductionmentioning

confidence: 96%

“…One route to the microstructuring and integration of GaP into a tandem configuration would involve the deposition of GaP on a structured template material 19. Si and GaP are nearly lattice matched (fractional lattice mismatch = 0.358%).…”

Section: Introductionmentioning

confidence: 99%

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Photoelectrochemical Behavior of Planar and Microwire‐Array Si|GaP Electrodes

Strandwitz

Turner-Evans

Tamboli

et al. 2012

Advanced Energy Materials

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Gallium phosphide exhibits a short diffusion length relative to its optical absorption length, and is thus a candidate for use in wire array geometries that allow light absorption to be decoupled from minority carrier collection. Herein is reported the photoanodic performance of heteroepitaxially grown gallium phosphide on planar and microwire‐array Si substrates. The n‐GaP|n‐Si heterojunction results in a favorable conduction band alignment for electron collection in the silicon. A conformal electrochemical contact to the outer GaP layer is produced using the ferrocenium/ferrocene (Fc+/Fc) redox couple in acetonitrile. Photovoltages of ∼750 mV under 1 sun illumination are observed and are attributed to the barrier formed at the (Fc+/Fc)|n‐GaP junction. The short‐circuit current densities of the composite microwire‐arrays are similar to those observed using single‐crystal n‐GaP photoelectrodes. Spectral response measurements along with a finite‐difference‐time‐domain optical model indicate that the minority carrier diffusion length in the GaP is ∼80 nm. Solid‐state current–voltage measurements show that shunting occurs through thin GaP layers that are present near the base of the microwire‐arrays. The results provide guidance for further studies of 3D multi‐junction photoelectrochemical cells.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

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Photoelectrochemical Behavior of Planar and Microwire‐Array Si|GaP Electrodes

Strandwitz

Turner-Evans

Tamboli

et al. 2012

Advanced Energy Materials

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“…Under 1 sun illumination, these diodes have an open circuit voltage of 660 mV, a short circuit current of 0.17 mA/cm 2 , and a fill factor of 42%. More details regarding structural and electrical characterization of our GaP layers are given elsewhere [10].…”

Section: Methodsmentioning

confidence: 99%

GaP/Si wire array solar cells

Tamboli

Turner-Evans

Malhotra

et al. 2010

2010 35th IEEE Photovoltaic Specialists Conference

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Si wire arrays have recently demonstrated their potential as photovoltaic devices [1][2][3]. Using these arrays as a base, we consider a next generation, multijunction wire array architecture consisting of Si wire arrays with a conformal GaNxP1-x-yAsy coating. Optical absorption and device physics simulations provide insight into the design of such devices. In particular, the simulations show that much of the solar spectrum can be absorbed as the angle of illumination is varied and that an appropriate choice of coating thickness and composition will lead to current matching conditions and hence provide a realistic path to high efficiencies. We have previously demonstrated high fidelity, high aspect ratio Si wire arrays grown by vaporliquid-solid techniques, and we have now successfully grown conformal GaP coatings on these wires as a precursor to considering quaternary compound growth. Structural, optical, and electrical characterization of these GaP/Si wire array heterostructures, including x-ray diffraction, Hall measurements, and optical absorption of polymer-embedded wire arrays using an integrating sphere were performed. The GaP epilayers have high structural and electrical quality and the ability to absorb a significant amount of the solar spectrum, making them promising for future multijunction wire array solar cells.

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“…This GaNP solar cell's efficiency is higher than other wide-bandgap solar cells: 2.42% 19 for an indirect bandgap GaP (2.26 eV), 3.89% 20 for direct bandgap InGaP (2.12 eV), and 4.8% 21 for direct bandgap GaAsP (1.92 eV). Although there are studies focused on the integration of III-V onto Si wires, [22][23][24][25] to the best of our knowledge, no similar studies have fabricated and discussed GaNP microwire solar cells to date.…”

Section: Introductionmentioning

confidence: 99%

Radial direct bandgap p-i-n GaNP microwire solar cells with enhanced short circuit current

Sukrittanon

Liu

Breeden³

et al. 2016

Journal of Applied Physics

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We report the demonstration of dilute nitride heterostructure core/shell microwire solar cells utilizing the combination of top-down reactive-ion etching to create the cores (GaP) and molecular beam epitaxy to create the shells (GaNP). Systematic studies of cell performance over a series of microwire lengths, array periods, and microwire sidewall morphologies examined by transmission electron microscopy were conducted to shed light on performance-limiting factors and to optimize the cell efficiency. We show by microscopy and correlated external quantum efficiency characterization that the open circuit voltage is degraded primarily due to the presence of defects at the GaP/GaNP interface and in the GaNP shells, and is not limited by surface recombination. Compared to thin film solar cells in the same growth run, the microwire solar cells exhibit greater short circuit current but poorer open circuit voltage due to greater light absorption and number of defects in the microwire structure, respectively. The comprehensive understanding presented in this work suggests that performance benefits of dilute nitride microwire solar cells can be achieved by further tuning of the epitaxial quality of the underlying materials.

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Conformal GaP layers on Si wire arrays for solar energy applications

Cited by 14 publications

References 17 publications

Photoelectrochemical Behavior of Planar and Microwire‐Array Si|GaP Electrodes

Photoelectrochemical Behavior of Planar and Microwire‐Array Si|GaP Electrodes

GaP/Si wire array solar cells

Radial direct bandgap p-i-n GaNP microwire solar cells with enhanced short circuit current

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