Managing Resonant and Nonresonant Lasing Modes in GaAs Nanowire Random Lasers.

Random lasers are promising, easy-to-fabricate light sources that rely on scattering instead of well-defined optical cavities. We demonstrate random lasing in GaAs nanowires using both randomly oriented and vertically aligned arrays. These configurations are shown to lase in both resonant and nonresonant modes, where aligned nanowires support predominantly resonant lasing and randomly oriented favors nonresonant lasing. On the basis of numerical simulations, aligning the nanowires increases the system's scattering efficiency leading to higher quality factor modes and thus favoring the resonant modes. We further demonstrate two methods to optically suppress resonant mode lasing by increasing the number of excited modes. The light output-light input curves show a pronounced kink for the resonant lasing mode while the nonresonant mode is kink-free. The resonant lasing modes may be used as tunable lasers, and the nonresonant modes exhibit near-thresholdless amplification. Switching between lasing modes opens up new opportunities to use lasers in broader applications.

Mechanical Behavior of InP Twinning Superlattice Nanowires.

Taper-free InP twinning superlattice (TSL) nanowires with an average twin spacing of ∼13 nm were grown along the zinc-blende close-packed [111] direction using metalorganic vapor phase epitaxy. The mechanical properties and fracture mechanisms of individual InP TSL nanowires in tension were ascertained by means of in situ uniaxial tensile tests in a transmission electron microscope. The elastic modulus, failure strain, and tensile strength along the [111] direction were determined. No evidence of inelastic deformation mechanisms was found before fracture, which took place in a brittle manner along the twin boundary. The experimental results were supported by molecular dynamics simulations of the tensile deformation of the nanowires that also showed that the fracture of twinned nanowires occurred in the absence of inelastic deformation mechanisms by the propagation of a crack from the nanowire surface along the twin boundary.

Broadband Phase-Sensitive Single InP Nanowire Photoconductive Terahertz Detectors.

Terahertz time-domain spectroscopy (THz-TDS) has emerged as a powerful tool for materials characterization and imaging. A trend toward size reduction, higher component integration, and performance improvement for advanced THz-TDS systems is of increasing interest. The use of single semiconducting nanowires for terahertz (THz) detection is a nascent field that has great potential to realize future highly integrated THz systems. In order to develop such components, optimized material optoelectronic properties and careful device design are necessary. Here, we present antenna-optimized photoconductive detectors based on single InP nanowires with superior properties of high carrier mobility (∼1260 cm(2) V(-1) s(-1)) and low dark current (∼10 pA), which exhibit excellent sensitivity and broadband performance. We demonstrate that these nanowire THz detectors can provide high quality time-domain spectra for materials characterization in a THz-TDS system, a critical step toward future application in advanced THz-TDS system with high spectral and spatial resolution.

Protocol on the fabrication of monocrystalline thin semiconductor via crack-assisted layer exfoliation technique for photoelectrochemical water-splitting.

Thin semiconductors attract huge interest due to their cost-effective, flexible, lightweight, and semi-transparent properties. Here, we present a protocol on the preparation of thin semiconductor via controlled crack-assisted layer exfoliation technique. The protocol details the fabrication procedure for producing thin monocrystalline semiconductors with thicknesses in the range of a few tens of micrometers from thick donor substrates. In addition, we describe proof-of-concept application of the thin semiconductors for photoelectrochemical water-splitting to produce hydrogen fuel. For complete details on the use and execution of this protocol, please refer to Lee et al. (2021).

Hole and Electron Effective Masses in Single InP Nanowires with a Wurtzite-Zincblende Homojunction.

The formation of wurtzite (WZ) phase in III-V nanowires (NWs) such as GaAs and InP is a complication hindering the growth of pure-phase NWs, but it can also be exploited to form NW homostructures consisting of alternate zincblende (ZB) and WZ segments. This leads to different forms of nanostructures, such as crystal-phase superlattices and quantum dots. Here, we investigate the electronic properties of the simplest, yet challenging, of such homostructures: InP NWs with a single homojunction between pure ZB and WZ segments. Polarization-resolved microphotoluminescence (µ-PL) measurements on single NWs provide a tool to gain insights into the interplay between NW geometry and crystal phase. We also exploit this homostructure to simultaneously measure effective masses of charge carriers and excitons in ZB and WZ InP NWs, reliably. Magneto-µ-PL measurements carried out on individual NWs up to 29 T at 77 K allow us to determine the free exciton reduced masses of the ZB and WZ crystal phases, showing the heavier character of the WZ phase, and to deduce the effective mass of electrons in ZB InP NWs (me= 0.080 m0). Finally, we obtain the reduced mass of light-hole excitons in WZ InP by probing the second optically permitted transition Γ7C ↔ Γ7uV with magneto-µ-PL measurements carried out at room temperature. This information is used to extract the experimental light-hole effective mass in WZ InP, which is found to be mlh = 0.26 m0, a value much smaller than the one of the heavy hole mass. Besides being a valuable test for band structure calculations, the knowledge of carrier masses in WZ and ZB InP is important in view of the optimization of the efficiency of solar cells, which is one of the main applications of InP NWs.

Three-dimensional cross-nanowire networks recover full terahertz state.

Terahertz radiation encompasses a wide band of the electromagnetic spectrum, spanning from microwaves to infrared light, and is a particularly powerful tool for both fundamental scientific research and applications such as security screening, communications, quality control, and medical imaging. Considerable information can be conveyed by the full polarization state of terahertz light, yet to date, most time-domain terahertz detectors are sensitive to just one polarization component. Here we demonstrate a nanotechnology-based semiconductor detector using cross-nanowire networks that records the full polarization state of terahertz pulses. The monolithic device allows simultaneous measurements of the orthogonal components of the terahertz electric field vector without cross-talk. Furthermore, we demonstrate the capabilities of the detector for the study of metamaterials.

High-Efficiency Solar Cells from Extremely Low Minority Carrier Lifetime Substrates Using Radial Junction Nanowire Architecture.

Currently, a significant amount of photovoltaic device cost is related to its requirement of high-quality absorber materials, especially in the case of III-V solar cells. Therefore, a technology that can transform a low-cost, low minority carrier lifetime material into an efficient solar cell can be beneficial for future applications. Here, we transform an inefficient p-type InP substrate with a minority carrier lifetime less than 100 ps into an efficient solar cell by utilizing a radial p-n junction nanowire architecture. We fabricate a p-InP/n-ZnO/AZO radial heterojunction nanowire solar cell to achieve a photovoltaic conversion efficiency of 17.1%, the best reported value for radial junction nanowire solar cells. The quantum efficiency of ∼95% (between 550 and 750 nm) and the short-circuit current density of 31.3 mA/cm2 are among the best for InP solar cells. In addition, we also perform an advanced loss analysis of the proposed solar cell to assess different loss mechanisms in the solar cell.