Semiconductor nanowire solar cells with single p-n junction have achieved comparable efficiency to their planar counterparts with substantial reduction of material consumption. Tandem geometry is a path towards even higher efficiency, for which a key step towards realizing such a device is the fabrication of tunnel (Esaki) diodes within nanowires with correct diameter, pitch, and material combination for maximized efficiency. We have fabricated, characterized and compared the electrical characteristics and material properties of InP/GaInP and GaInP/InP nanowire tunnel diodes with band gap combinations corresponding to high efficiency solar energy harvesting. Four different configurations with respect to material composition and doping were investigated. The nanowire arrays were grown with Metal Organic Vapor Phase Epitaxy from Au particles defined by use of nano imprint lithography, metal evaporation and lift-off. Electrical measurements show that the NWs behave as tunnel diodes in both InP (bottom)/GaInP (top) and GaInP (bottom)/InP (top) configurations, exhibiting a maximum peak current density of 25 A/cm 2 , and maximum peak to valley current ratio of 2.5 at room temperature. The realization of NW tunnel diodes in both InP/GaInP and GaInP/InP configurations open up an opportunity for NW tandem solar cells independent of the growth order of the different materials, opening up for flexibility regarding dopant incorporation polarity.

Articles you may be interested inInGaAs/GaAsP superlattice solar cells with reduced carbon impurity grown by low-temperature metal-organic vapor phase epitaxy using triethylgallium J. Appl. Phys. 116, 203101 (2014)

To harvest the benefits of III-V nanowires in optoelectronic devices, the development of ternary materials with controlled doping is needed. In this work, we performed a systematic study of n-type dopant incorporation in dense In GaP nanowire arrays using tetraethyl tin (TESn) and hydrogen sulfide (HS) as dopant precursors. The morphology, crystal structure and material composition of the nanowires were characterized by use of scanning electron microscopy, transmission electron microscopy and energy dispersive x-ray analysis. To investigate the electrical properties, the nanowires were broken off from the substrate and mechanically transferred to thermally oxidized silicon substrates, after which electron beam lithography and metal evaporation were used to define electrical contacts to selected nanowires. Electrical characterization, including four-probe resistivity and Hall effect, as well as back-gated field effect measurements, is combined with photoluminescence spectroscopy to achieve a comprehensive evaluation of the carrier concentration in the doped nanowires. We measure a carrier concentration of ∼1 × 10 cm in nominally intrinsic nanowires, and the maximum doping level achieved by use of TESn and HS as dopant precursors using our parameters is measured to be ∼2 × 10 cm, and ∼1 × 10 cm, respectively (by Hall effect measurements). Hence, both TESn and HS are suitable precursors for a wide range of n-doping levels in In GaP nanowires needed for optoelectronic devices, grown via the vapor-liquid-solid mode.

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InP nanowire p-type doping via Zinc indiffusionHaggren, Tuomas; Otnes, Gaute; Mourão, Renato; Dagyte, Vilgaile; Hultin, Olof; Lindelöw, Fredrik; Borgström, Magnus; Samuelson, Lars Growth, 451, 18-26. DOI: 10.1016/j.jcrysgro.2016 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. AbstractWe report an alternative pathway for p-type InP nanowire (NW) doping by indiffusion of Zn species from the gas phase. The indiffusion of Zn was performed in a MOVPE reactor at 350 -500 °C for 5 -20 min with either H 2 environment or additional phosphorus in the atmosphere. In addition, Zn 3 P 2 shells were studied as protective caps during post-diffusion annealing. This post-diffusion annealing was performed to outdiffuse and activate interstitial Zn. The InP NWs were characterized with photoluminescence and electrical measurements. The acquired carrier concentrations were in order of >10 17 cm -3 for NWs without post-annealing, and up to 10 18 cm -3 for NWs annealed with the Zn 3 P 2 shells. The indiffused Zn was evident additionally in the photoluminescence measurements.

Herein, two challenges are addressed, which quantum well infrared photodetectors (QWIPs), based on III-V semiconductors, face, namely: photodetection within the so-called "forbidden gap", between 1.7 and 2.5 microns, and room temperature operation using thermal sources. First, to reach this forbidden wavelength range, a QWIP which consists of a superlattice structure with a central quantum well (QW) with a different thickness is presented. The different QW in the symmetric structure, which plays the role of a defect in the otherwise periodic structure, gives rise to localized states in the continuum. The proposed InGaAs/InAlAs superlattice QWIP detects radiation around 2.1 microns, beyond the materials bandoffset. Additionally, the wavefunction parity anomaly is explored to increase the oscillator strength of the optical transitions involving higher order states. Second, with the purpose of achieving room temperature operation, an asymmetric InGaAs/InAlAs superlattice, in which the QW with a different thickness is not in the center, is used to detect infrared radiation around 4 microns at 300 K. This structure operates in the photovoltaic mode because it gives rise to states in the continuum which are localized in one direction and extended in the other, leading to a preferential direction for current flow.

InAs QDs embedded in an AlGaAs matrix have been produced by MOVPE with a partial capping and annealing technique to achieve controllable QD energy levels that could be useful for solar cell applications. The resulted spool-shaped QDs are around 5 nm in height and have a log-normal diameter distribution, which is observed by TEM to range from 5 to 15 nm. Two photoluminescence peaks associated with QD emission are attributed to the ground and the first excited states transitions. The luminescence peak width is correlated with the distribution of QD diameters through the diameter dependent QD energy levels.

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