III-V Semiconductor Nanowires Research Articles

(Invited) Photoluminescence Properties of Single InAsP Quantum Dots Embedded in InP Nanowires

Non-classical light emitters that can generate single photons with a negligible multiphoton probability are one of the key components for quantum information technologies. Deterministically grown III-V semiconductor nanowires containing quantum dots are gaining interest as a viable platform for quantum key distribution applications. In this talk, we will report on our recent development of the fabrication of InAsP single quantum dots embedded within InP photonic waveguide nanowires. In particular, we outline the importance of the photonic waveguide design for optimum photon generation and coupling to external optics [1]. The measured count rate dependence on normalized wire diameter, D/λ (figure 1) of the nanowire sources is consistent with calculations of the spontaneous emission rate into the fundamental HE11 nanowire waveguide mode (ΓHE11). Manipulating dot growth conditions and engineering the band structure around the dot (dot-in-a-rod configuration) are applied [2] to enhance the photoluminescence emission rate at 1310 nm and 1550 nm. Single photon emission with very low multiple photon probability is demonstrated at O- and C-band [3,4]. Temperature dependent, second-order correlation measurements on the 1310 nm source show that these nanowire sources can generate single photons up to temperatures of 220 K [3].[1] S. Haffouz, et al., Nano Letters, 18, 3047 (2018).[2] S. Haffouz, et al., Applied Physics Letters, 117, 113101 (2020).[3] P. Laferriére, et al., Nano Letters, 23, 962 (2023).[4] A.N. Wakileh, et al., arXiv:2309.13381 (2023). Figure 1

Optical Analysis of Perovskite III-V Nanowires Interpenetrated Tandem Solar Cells.

Multi-junction photovoltaics approaches are being explored to mitigate thermalization losses that occur in the absorption of high-energy photons. However, the design of tandem cells faces challenges such as light reflection and parasitic absorption. Nanostructures have emerged as promising solutions due to their anti-reflection properties, which enhances light absorption. III-V nanowires (NWs) solar cells can achieve strong power conversion efficiencies, offering the advantage of potentially integrating tunnel diodes within the same fabrication process. Metal halide perovskites (MHPs) have gained attention for their optoelectronic attributes and cost-effectiveness. Notably, both material classes allow for tunable bandgaps. This study explores the integration of MHPs with III-V NWs solar cells in both two-terminal and three-terminal configurations. Our primary focus lies in the optical analysis of a tandem design using III-V semiconductor nanowire arrays in combination with perovskites, highlighting their potential for tandem applications. The space offered by the compact footprint of NW arrays is used in an interpenetrated tandem structure. We systematically optimize the bottom cell, addressing reflectivity and parasitic absorption, and extend to a full tandem structure, considering experimentally feasible thicknesses. Simulation of a three-terminal structure highlights a potential increase in efficiency, decoupling the operating points of the subcells. The two-terminal analysis underscores the benefits of nanowires in reducing reflection and achieving a higher matched current between the top and the bottom cells. This research provides significant insights into NW tandem solar cell optics, enhancing our understanding of their potential to improve photovoltaic performance.

Axial Growth Characteristics of Optically Active InGaAs Nanowire Heterostructures for Integrated Nanophotonic Devices.

III-V semiconductor nanowire (NW) heterostructures with axial InGaAs active regions hold large potential for diverse on-chip device applications, including site-selectively integrated quantum light sources, NW lasers with high material gain, as well as resonant tunneling diodes and avalanche photodiodes. Despite various promising efforts toward high-quality single or multiple axial InGaAs heterostacks using noncatalytic growth mechanisms, the important roles of facet-dependent shape evolution, crystal defects, and the applicability to more universal growth schemes have remained elusive. Here, we report the growth of optically active InGaAs axial NW heterostructures via completely catalyst-free, selective-area molecular beam epitaxy directly on silicon (Si) using GaAs(Sb) NW arrays as tunable, high-uniformity growth templates and highlight fundamental relationships between structural, morphological, and optical properties of the InGaAs region. Structural, compositional, and 3D-tomographic characterizations affirm the desired directional growth along the NW axis with no radial growth observed. Clearly distinct luminescence from the InGaAs active region is demonstrated, where tunable array-geometry parameters and In content up to 20% are further investigated. Based on the underlying twin-induced growth mode, we further describe the facet-dependent shape and interface evolution of the InGaAs segment and its direct correlation with emission energy.

Absorption of Light in Vertical III-V Semiconductor Nanowires for Solar Cell and Photodetector Applications

Vertical III-V semiconductor nanowires have shown promising absorption of light for solar cell and photodetector applications. The absorption properties can be tuned through the choice of III-V materials and geometry of the nanowires. Here, we review the recent progress in the design of the absorption properties of both individual nanowires and nanowire arrays. Future directions for the research field are proposed.

Short-wave infrared cavity resonances in a single GeSn nanowire

Nanowires are promising platforms for realizing ultra-compact light sources for photonic integrated circuits. In contrast to impressive progress on light confinement and stimulated emission in III-V and II-VI semiconductor nanowires, there has been no experimental demonstration showing the potential to achieve strong cavity effects in a bottom-up grown single group-IV nanowire, which is a prerequisite for realizing silicon-compatible infrared nanolasers. Herein, we address this limitation and present an experimental observation of cavity-enhanced strong photoluminescence from a single Ge/GeSn core/shell nanowire. A sufficiently large Sn content ( ~ 10 at%) in the GeSn shell leads to a direct bandgap gain medium, allowing a strong reduction in material loss upon optical pumping. Efficient optical confinement in a single nanowire enables many round trips of emitted photons between two facets of a nanowire, achieving a narrow width of 3.3 nm. Our demonstration opens new possibilities for ultrasmall on-chip light sources towards realizing photonic-integrated circuits in the underexplored range of short-wave infrared (SWIR).

Giant reduction of thermal conductivity and enhancement of thermoelectric performance in twinning superlattice InAsSb nanowires

Semiconductor nanostructures hold great promise for high-efficiency waste-heat recovery exploiting thermoelectric energy conversion. They could significantly contribute to the implementation of environmentally friendly energy sources and to the realization of self-powered biomedical wearable devices. A crucial thermoelectric material requirement is a reduced thermal conductivity together with good electrical transport properties. In this work we demonstrate a drastic reduction of the thermal conductivity in III-V semiconductor nanowires as a result of the introduction of periodic crystal-lattice twin planes during growth. The electrical and thermal transport of these nanostructures, known as twinning superlattice nanowires, are probed and compared with their twin-free counterparts, showing a one order of magnitude decrease of thermal conductivity while maintaining unaltered electrical-transport properties and Seebeck coefficients. This leads to tenfold enhancement of the thermoelectric figure of merit, ZT. Our study reports for the first time the complete experimental measurement of electrical and thermal properties in twinning superlattice nanowires, demonstrating their emergence as a novel class of nanomaterials of great potential for high-efficiency thermoelectric-energy harvesting.

Revealing charge carrier dynamics and transport in Te-doped GaAsSb and GaAsSbN nanowires by correlating ultrafast terahertz spectroscopy and optoelectronic characterization

Recent advances in the growth of III-V semiconductor nanowires (NWs) hold great promise for nanoscale optoelectronic device applications. It is established that a small amount of nitrogen (N) incorporation in III-V semiconductor NWs can effectively red-shift their wavelength of operation and tailor their electronic properties for specific applications. However, understanding the impact of N incorporation on non-equilibrium charge carrier dynamics and transport in semiconducting NWs is critical in achieving efficient semiconducting NW devices. In this work, ultrafast optical pump-terahertz probe spectroscopy has been used to study non-equilibrium carrier dynamics and transport in Te-doped GaAsSb and dilute nitride GaAsSbN NWs, with the goal of correlating these results with electrical characterization of their equilibrium photo-response under bias and low-frequency noise characteristics. Nitrogen incorporation in GaAsSb NWs led to a significant increase in the carrier scattering rate, resulting in a severe reduction in carrier mobility. Carrier recombination lifetimes of 33 ± 1 picoseconds (ps) and 147 ± 3 ps in GaAsSbN and GaAsSb NWs, respectively, were measured. The reduction in the carrier lifetime and photoinduced optical conductivities are due to the presence of N-induced defects, leading to deterioration in the electrical and optical characteristics of dilute nitride NWs relative to the non-nitride NWs. Finally, we observed a very fast rise time of ∼2 ps for both NW materials, directly impacting their potential use as high-speed photodetectors.

Phase Control Growth of InAs Nanowires by Using Bi Surfactant

To realize practical applications of nanowire-based devices, it is critical, yet challenging, to control crystal structure growth of III-V semiconductor nanowires. Here, we demonstrate that controlled wurtzite and zincblende phases of InAs nanowires can be fabricated using bismuth (Bi) as a surfactant. For this purpose, catalyst free selective area epitaxial growth of InAs nanowires was performed using molecular beam epitaxy (MBE). During the growth, Bi was used which may act as a wetting agent influencing the surface energy at growth plane ends, promoting wurtzite crystal phase growth. For a demonstration, wurtzite and zincblende InAs nanowires were obtained with and without using Bi-flux. Photoluminescence spectroscopy (PL) analysis of the nanowires indicates a strong correlation between wurtzite phase and the Bi-flux. It is observed that the bandgap energy of wurtzite and zincblende nanowires are ∼0.50 eV and ∼0.42 eV, respectively, and agree well with theoretical estimated bandgap of corresponding InAs crystal phases. A blue shift in PL emission peak energy was found with decreasing nanowire diameter. The controlled wurtzite and zincblende crystal phase and its associated heterostructure growth of InAs nanowires on Si may open up new opportunities in bandgap engineering and related device applications integrated on Si. Furthermore, this work also illustrates that Bi as a surfactant could play a dynamic role in the growth mechanism of III-V compound semiconductors.

Different III-V semiconductor nanowires with quantum dots on silicon: growth by molecular-beam epitaxy and properties

Recently, III-V semiconductor nanostructures of reduced dimension attract more and more interest of researchers for the new generation devices creation. Combinations of nanostructures with different dimensions are of special interest, among them, for example, quantum dots in the body of nanowires. Such quantum dotsʼ size and location control is strictly determined by the growth parameters. As a result of effective relaxation of mechanical stresses on the lateral faces of nanowires, the integration of hybrid nanostructures with silicon technology is possible. In this work, we have demonstrated the possibility of GaP nanowires with GaAs quantum dots and AlGaP nanowires with InGaP quantum dots growth on silicon by molecular-beam epitaxy. The physical properties of the selected nanowires have been investigated. Growth experiments were performed using Riber Compact 21 setup, which is equipped, in addition to the growth chamber, with a vacuum-aligned chamber for gold deposition (metallization chamber). The morphological properties of the obtained nanostructures were studied by scanning electron microscopy. The optical properties of the nanostructures were investigated by the photoluminescence method. The analyses of morphological properties showed that GaP nanowires with GaAs quantum dots were formed predominantly in the <111> direction, in contrast to AlGaP nanowires with InGaP quantum dots, which in some cases changed the growth direction. The reason for the change in the direction of growth of nanowires may be the participation of indium in the growth process. With a sufficient content of indium in the gold catalyst droplet, such mixed droplet can etch the facets at the top of the nanowires, thereby descending to the side of the nanowires and changing the direction of nanowires growth. The studies of the optical properties of the grown nanostructures showed that the photoluminescence signal from InGaP quantum dots in AlGaP nanowires is observed at a temperature of –263 °C with a peak maximum of around 550 nm. Thus, the synthesized nanostructures are promising for optoelectronic applications, in particular, for creating sources of single-photons.

Thermoelectric Characteristics of InAs Nanowire Networks Directly Grown on Flexible Plastic Substrates

III-V semiconductor nanowires have shown promise for thermoelectric applications, but their use in practical devices has conventionally been hindered by complex fabrication processes and device integration. Here, we characterize the thermoelectric properties of InAs nanowire networks directly grown on flexible polyimide plastic. The n-type nanowire networks achieve a high room-temperature Seebeck coefficient of −110.8 μV K–1 and electrical conductivity of 41 S cm–1, resulting in a thermoelectric power factor of 50.4 μW m–1 K–2. Moreover, the nanowire networks show remarkable mechanical flexibility with a relative change in resistance below 0.01 at bending radii below 5.2 mm. We further establish the thermoelectric performance of InAs nanowire networks on plastic using a facile proof-of-concept thermoelectric generator producing a maximum power of 0.44 nW at a temperature gradient of 5 K. The findings indicate that direct growth of III-V nanowire networks on plastic substrates shows promise for the development of flexible thermoelectrics applications.

Slowing Hot-Electron Relaxation in Mix-Phase Nanowires for Hot-Carrier Photovoltaics.

Hot carrier harvest could save 30% energy loss in solar cells. So far, however, it is still unreachable as the photoexcited hot carriers are short-lived, ∼1 ps, determined by a rapid relaxation process, thus invalidating any reprocessing efforts. Here, we propose and demonstrate a feasible route to reserve hot electrons for efficient collection. It is accomplished by an intentional mix of cubic zinc-blend and hexagonal wurtzite phases in III-V semiconductor nanowires. Additional energy levels are then generated above the conduction band minimum, capturing and storing hot electrons before they cool down to the band edges. We also show the superiority of core/shell nanowire (radial heterostructure) in extracting hot electrons. The strategy disclosed here may offer a unique opportunity to modulate hot carriers for efficient solar energy harvest.

Surface Nano-Patterning for the Bottom-Up Growth of III-V Semiconductor Nanowire Ordered Arrays.

Ordered arrays of vertically aligned semiconductor nanowires are regarded as promising candidates for the realization of all-dielectric metamaterials, artificial electromagnetic materials, whose properties can be engineered to enable new functions and enhanced device performances with respect to naturally existing materials. In this review we account for the recent progresses in substrate nanopatterning methods, strategies and approaches that overall constitute the preliminary step towards the bottom-up growth of arrays of vertically aligned semiconductor nanowires with a controlled location, size and morphology of each nanowire. While we focus specifically on III-V semiconductor nanowires, several concepts, mechanisms and conclusions reported in the manuscript can be invoked and are valid also for different nanowire materials.

Robust Protection of III-V Nanowires in Water Splitting by a Thin Compact TiO2 Layer.

Narrow-band-gap III–V semiconductor nanowires (NWs) with a suitable band structure and strong light-trapping ability are ideal for high-efficiency low-cost solar water-splitting systems. However, due to their nanoscale dimension, they suffer more severe corrosion by the electrolyte solution than the thin-film counterparts. Thus, short-term durability is the major obstacle for using these NWs for practical water-splitting applications. Here, we demonstrated for the first time that a thin layer (∼7 nm thick) of compact TiO2 deposited by atomic layer deposition can provide robust protection to III–V NWs. The protected GaAs NWs maintain 91.4% of its photoluminescence intensity after 14 months of storage in ambient atmosphere, which suggests the TiO2 layer is pinhole-free. Working as a photocathode for water splitting, they exhibited a 45% larger photocurrent density compared with unprotected counterparts and a high Faraday efficiency of 91% and can also maintain a record-long highly stable performance among narrow-band-gap III–V NW photoelectrodes; after 67 h photoelectrochemical stability test reaction in a strong acid electrolyte solution (pH = 1), they show no apparent indication of corrosion, which is in stark contrast to the unprotected NWs that fully failed after 35 h. These findings provide an effective way to enhance both stability and performance of III–V NW-based photoelectrodes, which are highly important for practical applications in solar-energy-based water-splitting systems.

Gate Bias Stress Instability and Hysteresis Characteristics of InAs Nanowire Field-Effect Transistors.

Because of the excellent electrical properties, III-V semiconductor nanowires are promising building blocks for next-generation electronics; however, their rich surface states inevitably contribute large amounts of charge traps, leading to gate bias stress instability and hysteresis characteristics in nanowire field-effect transistors (FETs). Here, we investigated thoroughly the gate bias stress and hysteresis effects in InAs nanowire FETs. It is observed that the output current decreases together with the threshold voltage shifting to the positive direction when a positive gate bias stress is applied, and vice versa for the negative gate bias stress. For double-sweep transfer characteristics, the significant hysteresis behavior is observed, depending heavily on the sweeping rate and range. On the basis of complementary investigations of these devices, charge traps are confirmed to be the dominant factor for these instability effects. Importantly, the hysteresis can be simulated well by utilizing a combination of the rate equation for electron density and the empirical model for electron mobility. This provides an accurate evaluation of carrier mobility, which is in distinct contrast to the overestimation of mobility when using the transconductance for calculation. All these findings are important for understanding the charge trap dynamics to further enhance the device performance of nanowire FETs.

(Invited) Atomistic Understanding on the Surface of GaAs By Ab Initio Thermodynamics; From Equilibrium Shape to Growth Shape

The III-V semiconductor nanowires (NWs) have attracted substantial attention as an ideal system for the study on the growth mechanism and electronic device applications. For the precise manipulation of the nanowire growth, understanding on the temperature–pressure (T–P) dependent variation in surface energy and reconstruction which governs the anisotropic interaction between vapor sources and crystal solids is crucial. Unfortunately, the quantitative values of the variation in surface energy cannot be obtained only using the conventional electronic structure calculation. To overcome this difficulty, we have developed a reliable ab initio thermodynamic method by which the T–P dependent surface energy is predicted from the atomic-scale calculations on: surface reconstructions of InAs1; equilibrium crystal shapes of GaAs and InAs2; and anisotropic adsorption and growth conditions of GaAs NW3.In this talk, we present an ab initio thermodynamics approach by combining the atomic-scale calculation with the thermodynamic treatment to take a step forward in the theoretical modeling on the growth of polar GaAs <111> nanowire by calculating the change in Gibbs free energy during the nucleation and growth process. By comparing the nucleation rate between different stacking sequences, the formation probability of stacking fault or wurtzite segment was quantitatively predicted under arbitrary vapor-phase growth conditions. The predicted T–P dependent probability from atomic-scale calculation is directly comparable to the experiments and remarkably consistent with the available results to date, elucidating the fundamental asymmetric growth mechanism. Our ab initio approach is truly independent of any empirical data, bridging to the experimentally controllable variables. This simulation can be applied to various nanomaterials, including two-dimensional materials as well as other III-V and II-VI NWs, where the precise control of the stacking sequence is significant for their properties.[1] Yeu et al., Sci. Rep., 2017, 7, 10691[2] Yeu et al., Sci. Rep., 2019, 9, 1127[3] Yeu et al., Appl. Surf., Sci., 2019, 497, 143740

Performance improvement of InP nanowire array solar cells by decorated nanowires and using back reflector

Abstract Geometrical design of the vertical arrays of III-V semiconductor nanowires (NWs) is a good candidate for optoelectronic devices due to their ability to excite nanophotonic resonances in the absorption spectrum. Since the appropriate tailoring of radius, length, and pitch is an effective factor in the light absorption of NWs, we first determine the radius and pitch of NWs in which the light absorption of the array is almost the same for different lattices. Then the length at which the best absorption occurs in the NWs is calculated. The plasmonic effect on the performance of the solar cell array is then investigated by calculating the array properties such as adsorption and short-circuit current density using the finite-difference time-domain (FDTD) numerical model. The plasmonic nanostructure is a composite light-trapping structure in which NWs are decorated with gold nanoparticles and an array of gold hemispheres is placed at the rear of the surface as a back reflector. Various geometric shapes such as spheres, cubes, hemispheres, and disks were used to decorate NW with gold nanoparticles, among them spherical gold nanoparticles were more absorbed than other geometric shapes at higher wavelengths, especially at a wavelength close to the bandgap, where most photons are not trapped. It is observed that this light-trapping structure excites plasmonic modes and improves absorption of NWs. Based on FDTD simulation results, the short-circuit current density and maximum photovoltaic efficiency are respectively improved by 8.56% and 13.33% in the proposed structure compared to the bare structure.

Perovskite-Gallium Phosphide Platform for Reconfigurable Visible-Light Nanophotonic Chip.

Reduction of the wavelength in on-chip light circuitry is critically important not only for the sake of keeping up with Moore's law for photonics but also for reaching toward the spectral ranges of operation of emerging materials, such as atomically thin semiconductors, vacancy-based single-photon emitters, and quantum dots. This requires efficient and tunable light sources as well as compatible waveguide networks. For the first challenge, halide perovskites are prospective materials that enable cost-efficient fabrication of micro- and nanolasers. On the other hand, III-V semiconductor nanowires are optimal for guiding of visible light as they exhibit a high refractive index as well as excellent shape and crystalline quality beneficial for strong light confinement and long-range waveguiding. Here, we develop an integrated platform for visible light that comprises gallium phosphide (GaP) nanowires directly embedded into compact CsPbBr3-based light sources. In our devices, perovskite microcrystals support stable room-temperature lasing and broadband chemical tuning of the emission wavelength in the range of 530-680 nm, whereas GaP nanowaveguides support efficient outcoupling of light, its subwavelength (<200 nm) confinement, and long-range guiding over distances more than 20 μm. As a highlight of our approach, we demonstrate sequential transfer and conversion of light using an intermediate perovskite nanoparticle in a chain of GaP nanowaveguides.

Formation Mechanism of Twinning Superlattices in Doped GaAs Nanowires.

Recent investigations of III-V semiconductor nanowires have revealed periodic zinc-blende twins, known as twinning superlattices, that are often induced by a high-impurity dopant concentration. In the present study, the relationship between the nanowire morphology, crystal structure, and impurity dopant concentration (Te and Be) of twinning superlattices has been studied in GaAs nanowires grown by molecular beam epitaxy using the self-assisted (with a Ga droplet) vapor-liquid-solid process. The contact angle between the Ga droplet and the nanowire top facet decreased linearly with the dopant concentration, whereas the period of the twinning superlattices increased with the doping concentration and was proportional to the nanowire radius. Our model, which is based entirely on surface energetics, is able to explain a unified formation mechanism of twinning superlattices in doped semiconductor nanowires.

Review on III-V Semiconductor Single Nanowire-Based Room Temperature Infrared Photodetectors.

Recently, III-V semiconductor nanowires have been widely explored as promising candidates for high-performance photodetectors due to their one-dimensional morphology, direct and tunable bandgap, as well as unique optical and electrical properties. Here, the recent development of III-V semiconductor-based single nanowire photodetectors for infrared photodetection is reviewed and compared, including material synthesis, representative types (under different operation principles and novel concepts), and device performance, as well as their challenges and future perspectives.

Highly uniform InGaAs/InP quantum well nanowire array-based light emitting diodes

III-V semiconductor nanowire infrared light emitting diodes (LEDs) have great potential for the development of Si-based integrated photonics. In this paper, we report the growth of highly uniform triangular prism InGaAs/InP single quantum well (QW) nanowires using a 2-step growth by metal organic chemical vapour deposition by selective area epitaxy technique. Based on these nanowire arrays, we demonstrate nanowire array LEDs with strong electroluminescence at two main peaks, originating from the axial and radial QW respectively and control the relative emission of those two peaks. We further reveal that a long lateral contact of the nanowire LED results in more intense radial QW emission by shortening the current path to the radial quantum well. Our study provides an important foundation for the development of high-performance array nanowire-based devices such as high-power multi-wavelength LEDs, high power electrically switchable wavelength-selectors and QW infrared photodetectors.