Doping incorporation paths in catalyst-free Be-doped GaAs nanowires

Casadei, Alberto; Krogstrup, Peter; Heiß, Martin; Röhr, Jason A.; Colombo, Carlo; Ruelle, Thibaud; Upadhyay, Shivendra; Sørensen, C. B.; Nygård, Jesper; Morral, Anna Fontcuberta i

doi:10.1063/1.4772020

Cited by 65 publications

(91 citation statements)

References 35 publications

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“…The gallium nominal growth rate was 900 nm h 21 , the substrate temperature was 630 8C and the V/III ratio was 4 (refs 43,44). The p-doping of the core was achieved by adding a flux of beryllium during axial growth 45 . Cores were annealed for 10 min at 630 8C.…”

Section: Methodsmentioning

confidence: 99%

Single-nanowire solar cells beyond the Shockley–Queisser limit

Jørgensen²,

et al. 2013

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Light management is of great importance in photovoltaic cells, as it determines the fraction of incident light entering the device. An optimal p-n junction combined with optimal light absorption can lead to a solar cell efficiency above the Shockley-Queisser limit. Here, we show how this is possible by studying photocurrent generation for a single core-shell p-i-n junction GaAs nanowire solar cell grown on a silicon substrate. At 1 sun illumination, a short-circuit current of 180 mA cm -2 is obtained, which is more than one order of magnitude higher than that predicted from the Lambert-Beer law. The enhanced light absorption is shown to be due to a light-concentrating property of the standing nanowire, as shown by photocurrent maps of the device. The results imply new limits for the maximum efficiency obtainable with III-V based nanowire solar cells under 1 sun illumination.N anowire-based solar cells hold great promise for third-generation photovoltaics and for powering nanoscale devices 1,2 . With the advent of third-generation photovoltaics, solar cells will become cheaper and more efficient than current devices. In particular, a cost reduction may be achieved by reducing material use through the fabrication of nanowire arrays and radial p-n junctions [3][4][5] . The geometry of nanowire crystals is expected to favour elastic strain relaxation, providing great freedom in the design of new compositional multijunction solar cells 6 grown on mismatched materials 7,8 . The efficiencies of nanostructured solar cells have increased over time and have now reached up to 13.8%, due to improvements in materials and new device concepts [9][10][11][12][13][14] .Light absorption in standing nanowires is a complex phenomenon, with a strong dependence on nanowire dimensions and the absorption coefficient of the raw materials [15][16][17][18] . In low-absorbing microwire arrays, such as those composed of silicon, light absorption is understood via ray optics or by calculation of the integrated local density of optical states of the nanowire film 19,20 . Interestingly, when these arrays stand on a Lambertian back-reflector, an asymptotic increase in light trapping for low filling factors (FFs) is predicted 19 . This is advantageous for improvement of the efficiency-to-cost ratio of solar cells and has led to the demonstration of microwire arrays exhibiting higher absorption than in the equivalent thickness of textured film 19,21,22 . The case for nanowires is quite different. Nanowire diameters are smaller than or comparable to the radiation wavelength. In this case, optical interference and guiding effects play a dominant role in relation to reflectivity and absorption spectra. For low-absorbing materials (for example, indirect bandgap materials such as silicon), waveguiding effects plays a key role 23,24 , whereas highly absorbing semiconductors (such as direct-bandgap GaAs) exhibit resonances that increase the total absorption several times. Nanowires lying on a substrate also exhibit such resonances, often described by Mi...

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Section: Methodsmentioning

confidence: 99%

Single-nanowire solar cells beyond the Shockley–Queisser limit

Jørgensen²,

et al. 2013

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“…Our GaAs nanowires are readily doped p-type with Be, which incorporates preferentially via the nanowire side facets enabling structures with an undoped core and Be-doped shell [25]. A Be-doped shell provides an ideal interface for AuBe contacts with narrow Schottky barrier and thereby p-type NWFETs with low resistance ohmic contacts.…”

Section: Resultsmentioning

confidence: 99%

“…This makes the Schottky barrier depletion region very narrow, raising the electron tunnelling probability and giving a linear I-V characteristic for the contact. This can be assisted by doping the semiconductor local to the contact by other means, e.g., by ion-implantation [28], or during growth [25,29].…”

Section: Resultsmentioning

confidence: 99%

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Near-thermal limit gating in heavily doped III-V semiconductor nanowires using polymer electrolytes

Ullah

Carrad

Krogstrup

et al. 2018

Phys. Rev. Materials

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Doping is a common route to reducing nanowire transistor on-resistance but has limits. High doping level gives significant loss in gate performance and ultimately complete gate failure. We show that electrolyte gating remains effective even when the Be doping in our GaAs nanowires is so high that traditional metal-oxide gates fail. In this regime we obtain a combination of subthreshold swing and contact resistance that surpasses the best existing p-type nanowire MOSFETs. Our sub-threshold swing of 75 mV/dec is within 25% of the room-temperature thermal limit and comparable with n-InP and n-GaAs nanowire MOSFETs. Our results open a new path to extending the performance and application of nanowire transistors, and motivate further work on improved solid electrolytes for nanoscale device applications.

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“…The core was obtained by the self-catalysed Ga-assisted process (VLS) [34][35][36][37], with a nominal gallium growth rate of 0.27 μm/h, for 45 min, at T = 630°C and V/III beam equivalent flux ratio of 60. The p-doping was achieved with a beryllium flux corresponding to a doping level of 3.5 × 10 19 atoms/cm 3 for planar growth [38]. The core diameter was about 120 nm.…”

Section: Nanowire Growthmentioning

confidence: 99%

Electrical contacts to single nanowires: a scalable method allowing multiple devices on a chip. Application to a single nanowire radial p-i-n junction

Heiß

Colombo

Mallorquí

et al. 2013

IJNT

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Semiconductor nanowires are currently at the forefront of research in the areas of nanoelectronics and energy conversion. In all these studies, realising electrical contacts and statistically relevant measurements is a key issue. We propose a method that enables to contact hundreds of nanowires on a single wafer in an extremely fast electron beam lithography session. The method is applied to nanowire-based radial GaAs p-i-n junction. Currentvoltage characteristics are shown, along with scanning photocurrent mapping.

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Doping incorporation paths in catalyst-free Be-doped GaAs nanowires

Cited by 65 publications

References 35 publications

Single-nanowire solar cells beyond the Shockley–Queisser limit

Single-nanowire solar cells beyond the Shockley–Queisser limit

Near-thermal limit gating in heavily doped III-V semiconductor nanowires using polymer electrolytes

Electrical contacts to single nanowires: a scalable method allowing multiple devices on a chip. Application to a single nanowire radial p-i-n junction

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