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Vertical III-V nanowire (NW) arrays are promising candidates for infrared (IR) photodetection applications. Generally, NWs with large diameters are required for efficient absorption in the IR range. However, increasing the NW diameter results in a loss of spectral selectivity and an enhancement in the photodetector dark current. Here, we propose a nanophotonic engineering approach to achieving spectrally-selective light absorption while minimizing the volume of the absorbing medium. Based on simulations performed using rigorous coupled-wave analysis (RCWA) techniques, we demonstrate dramatic tunability of the short-wavelength infrared (SWIR) light absorption properties of InAs NWs with base segments embedded in a reflective backside Au layer and with partial GaAs_0.1Sb_0.9shell segment coverage. Use of a backside reflector results in the generation of a delocalized evanescent field around the NW core segment that can be selectively captured by the partially encapsulating GaAs_0.1Sb_0.9shell layer. By adjusting the core and shell dimensions, unity absorption can be selectively achieved in the 2 to 3μm wavelength range. Due to the transparency of the GaAs_0.1Sb_0.9shell segments, wavelength-selective absorption occurs only along the InAs core segments where they are partially encapsulated. The design presented in this work paves the path toward spectrally-selective and polarization-dependent NW array-based photodetectors, in which carrier collection efficiencies can be enhanced by positioning active junctions at the predefined locations of the partial shell segments.

 

Self-assembly of vertically aligned III–V semiconductor nanowires (NWs) on two-dimensional (2D) van der Waals (vdW) nanomaterials allows for integration of novel mixed-dimensional nanosystems with unique properties for optoelectronic and nanoelectronic device applications. Here, selective-area vdW epitaxy (SA-vdWE) of InAs NWs on isolated 2D molybdenum disulfide (MoS 2 ) domains is reported for the first time. The MOCVD growth parameter space ( i.e. , V/III ratio, growth temperature, and total molar flow rates of metalorganic and hydride precursors) is explored to achieve pattern-free positioning of single NWs on isolated multi-layer MoS 2 micro-plates with one-to-one NW-to-MoS 2 domain placement. The introduction of a pre-growth poly- l -lysine surface treatment is highlighted as a necessary step for mitigation of InAs nucleation along the edges of triangular MoS 2 domains and for NW growth along the interior region of 2D micro-plates. Analysis of NW crystal structures formed under the optimal SA-vdWE condition revealed a disordered combination of wurtzite and zinc-blend phases. A transformation of the NW sidewall faceting structure is observed, resulting from simultaneous radial overgrowth during axial NW synthesis. A common lattice arrangement between axially-grown InAs NW core segments and MoS 2 domains is described as the epitaxial basis for vertical NW growth. A model is proposed for a common InAs/MoS 2 sub-lattice structure, consisting of three multiples of the cubic InAs unit cell along the [21̄1̄] direction, commensurately aligned with a 14-fold multiple of the Mo–Mo (or S–S) spacing along the [101̄0] direction of MoS 2 hexagonal lattice. The SA-vdWE growth mode described here enables controlled hybrid integration of mixed-dimensional III–V-on-2D heterostructures as novel nanosystems for applications in optoelectronics, nanoelectronics, and quantum enabling technologies. 

ABSTRACT Rigorous coupled wave analysis (RCWA) simulation was used to model the absorption in periodic arrays of GaAs(0.73)P(0.27) nanowires (NWs) on Si substrates dependent upon the diameter (D), length (L), and spacing (center-to-center distance, or pitch, P) of the NWs. Based on this study, two resonant arrangements for a top NW array sub-cell having the highest limiting short-circuit current densities (J_sc) were found to be close to D = 150 nm, P = 250 nm and D = 300 nm, P = 500 nm, both featuring the same packing density of 0.28. Even though a configuration with thinner NWs exhibited the highest J_sc = 19.46 mA/cm^2, the array with D = 350 nm and P = 500 nm provided current matching with the underlying Si sub-cell with J_sc = 18.59 mA/cm^2. Addition of a rear-side In(0.81)Ga(0.19)As nanowire array with D = 800 nm and P = 1000 nm was found to be suitable for current matching with the front NW sub-cell and middle Si. However, with thinner and sparser In(0.81)Ga(0.19)As NWs with D = 700 nm and P = 1000 nm, the J_scof the bottom sub-cell was increased from 17.35 mA/cm^2 to 18.76 mA/cm^2 using a planar metallic back surface reflector, thus achieving a current matching with the top and middle cells. 

Heterogeneous self-assembly of III–V nanostructures on inert two-dimensional monolayer materials enables novel hybrid nanosystems with unique properties that can be exploited for low-cost and low-weight flexible optoelectronic and nanoelectronic device applications. Here, the pseudo-van der Waals epitaxy (vdWE) growth parameter space for heterogeneous integration of InAs nanowires (NWs) with continuous films of single layer graphene (SLG) via metalorganic chemical vapor deposition (MOCVD) is investigated. The length, diameter, and number density of NWs, as well as areal coverage of parasitic islands, are quantified as functions of key growth variables including growth temperature, V/III ratio, and total flow rate of metalorganic and hydride precursors. A compromise between self-assembly of high aspect ratio NWs comprising high number density arrays and simultaneous minimization of parasitic growth coverage is reached under a selected set of optimal growth conditions. Exploration of NW crystal structures formed under various growth conditions reveals that a characteristic polytypic and disordered lattice is invariant within the explored parameter space. A growth evolution study reveals a gradual reduction in both axial and radial growth rates within the explored timeframe for the optimal growth conditions, which is attributed to a supply-limited competitive growth regime. Two strategies are introduced for further growth optimization. Firstly, it is shown that the absence of a pre-growth in situ arsine surface treatment results in a reduction of parasitic island coverage by factor of ∼0.62, while NW aspect ratio and number densities are simultaneously enhanced. Secondly, the use of a two-step flow-modulated growth procedure allows for realization of dense fields of high aspect ratio InAs NWs. As a result of the applied studies and optimization of the growth parameter space, the highest reported axial growth rate of 840 nm min −1 and NW number density of ∼8.3 × 10 8 cm −2 for vdWE of high aspect ratio (>80) InAs NW arrays on graphitic surfaces are achieved. This work is intended to serve as a guide for vdWE of self-assembled III–V semiconductor NWs such as In-based ternary and quaternary alloys on functional two-dimensional monolayer materials, toward device applications in flexible optoelectronics and tandem-junction photovoltaics. 

Vertically-aligned, high aspect ratio In InAsyP1-y, InxAl1-xAs, and core-shell InAsP-InP nanowires (NWs) are grown directly on two-dimensional (2-D) monolayer graphene via seed-free pseudo-van der Waals epitaxy (vdWE), as reported here for the first time. Growth is achieved using metalorganic chemical vapor deposition (MOCVD). By altering growth temperature and molar flow ratio of precursors, the composition Of InAsyP1-y NWs can be tuned within the 1 ≤ y ≤ 0.8 range. Similarly, by tuning the group-III precursor flow rates, InxAl1-x As composition can be modified in the range. NW morphology and NW array number density variances are measured for different ternary compositions as functions of precursor flow rates and growth temperature. 

Here presented are the properties and performance of a new metallo‐dielectric waveguide array structure as the encapsulation material for silicon solar cells. The arrays are produced through light‐induced self‐writing combined with in situ photochemical synthesis of silver nanoparticles. Each waveguide comprises a cylindrical core consisting of a high refractive index polymer and silver nanoparticles homogenously dispersed in its medium, all of which are surrounded by a low refractive index common cladding. The waveguide array‐based films are processed directly over a silicon solar cell. Arrays with systematically varied concentration of AgSbF₆as the salt precursor are explored. The structures are tested for their wide‐angle light capture capabilities, specifically toward enhanced conversion efficiency and current production of encapsulated solar cells. Observed are increases in the external quantum efficiency, especially at wide incident angles up to 70°, and nominal increases in the short circuit current density by 1 mA cm⁻²(relative to an array without nanoparticles). Enhanced light collection is explained in terms of the beneficial effect of scattering by the nanoparticles along the waveguide cores. This is a promising approach toward solar cell encapsulants that aid to increase solar cell output over both the course of the day and year.

 

Metal‐assisted chemical etching (MacEtch) has shown tremendous success as an anisotropic wet etching method to produce ultrahigh aspect ratio semiconductor nanowire arrays, where a metal mesh pattern serves as the catalyst. However, producing vertical via arrays using MacEtch, which requires a pattern of discrete metal disks as the catalyst, has often been challenging because of the detouring of individual catalyst disks off the vertical path while descending, especially at submicron scales. Here, the realization of ordered, vertical, and high aspect ratio silicon via arrays by MacEtch is reported, with diameters scaled from 900 all the way down to sub‐100 nm. Systematic variation of the diameter and pitch of the metal catalyst pattern and the etching solution composition allows the extraction of a physical model that, for the first time, clearly reveals the roles of the two fundamental kinetic mechanisms in MacEtch, carrier generation and mass transport. Ordered submicron diameter silicon via arrays with record aspect ratio are produced, which can directly impact the through‐silicon‐via technology, high density storage, photonic crystal membrane, and other related applications.