Doping Incorporation in InAs nanowires characterized by capacitance measurements

Sn and Se dopedInAsnanowires are characterized using a capacitance-voltage technique where the threshold voltages of nanowirecapacitors with different diameter are determined and analyzed using an improved radial metal-insulator-semiconductor field-effect transistor model. This allows for a separation of doping in the core of the nanowire from the surface charge at the side facets of the nanowire. The data show that the doping level in the InAsnanowire can be controlled on the level between 2×10¹⁸ to 1×10¹⁹ cm¯³, while the surface charge density exceeds 5×10¹² cm¯² and is shown to increase with higher dopant precursor molar fraction.This work was supported by the Swedish Research Council, the Swedish Foundation for Strategic Research, VINNOVA, the EU-project NODE 015783 and the Knut and Alice Wallenberg Foundation

In_<i>x</i>Ga_1–<i>x</i>P Nanowire Growth Dynamics Strongly Affected by Doping Using Diethylzinc

Semiconductor nanowires are versatile building blocks for optoelectronic devices, in part because nanowires offer an increased freedom in material design due to relaxed constraints on lattice matching during the epitaxial growth. This enables the growth of ternary alloy nanowires in which the bandgap is tunable over a large energy range, desirable for optoelectronic devices. However, little is known about the effects of doping in the ternary nanowire materials, a prerequisite for applications. Here we present a study of p-doping of In_<i>x</i>Ga_1–<i>x</i>P nanowires and show that the growth dynamics are strongly affected when diethylzinc is used as a dopant precursor. Specifically, using in situ optical reflectometry and high-resolution transmission electron microscopy we show that the doping results in a smaller nanowire diameter, a more predominant zincblende crystal structure, a more Ga-rich composition, and an increased axial growth rate. We attribute these effects to changes in seed particle wetting angle and increased TMGa pyrolysis efficiency upon introducing diethylzinc. Lastly, we demonstrate degenerate p-doping levels in In_<i>x</i>Ga_1–<i>x</i>P nanowires by the realization of an Esaki tunnel diode. Our findings provide insights into the growth dynamics of ternary alloy nanowires during doping, thus potentially enabling the realization of such nanowires with high compositional homogeneity and controlled doping for high-performance optoelectronics devices

Tunnel Field-Effect Transistors Based on InP-GaAs Heterostructure Nanowires

We present tunneling field-effect transistors fabricated from InP-GaAs heterostructure nanowires with an <i>n-i-p</i> doping profile, where the intrinsic InP region is modulated by a top gate. The devices show an inverse subthreshold slope down to 50 mV/dec averaged over two decades with an on/off current ratio of approximately 10⁷ for a gate voltage swing (<i>V</i>_GS) of 1 V and an on-current of 2.2 μA/μm. Low-temperature measurements suggest a mechanism of trap-assisted tunneling, possibly explained by a narrow band gap segment of InGaAsP

Optical Far-Field Method with Subwavelength Accuracy for the Determination of Nanostructure Dimensions in Large-Area Samples

The physical, chemical, and biological properties of nanostructures depend strongly on their geometrical dimensions. Here we present a fast, noninvasive, simple-to-perform, purely optical method that is capable of characterizing nanostructure dimensions over large areas with an accuracy comparable to that of scanning electron microscopy. This far-field method is based on the analysis of unique fingerprints in experimentally measured reflectance spectra using full three-dimensional optical modeling. We demonstrate the strength of our method on large-area (millimeter-sized) arrays of vertical InP nanowires, for which we simultaneously determine the diameter and length as well as cross-sample morphological variations thereof. Explicitly, the diameter is determined with an accuracy better than 10 nm and the length with an accuracy better than 30 nm. The method is versatile and robust, and we believe that it will provide a powerful and standardized measurement technique for large-area nanostructure arrays suitable for both research and industrial applications

Electron Trapping in InP Nanowire FETs with Stacking Faults

Semiconductor III–V nanowires are promising components of future electronic and optoelectronic devices, but they typically show a mixed wurtzite-zinc blende crystal structure. Here we show, theoretically and experimentally, that the crystal structure dominates the conductivity in such InP nanowires. Undoped devices show very low conductivities and mobilities. The zincblende segments are quantum wells orthogonal to the current path and our calculations indicate that an electron concentration of up to 4.6 × 10¹⁸ cm^–3 can be trapped in these. The calculations also show that the room temperature conductivity is controlled by the longest zincblende segment, and that stochastic variations in this length lead to an order of magnitude variation in conductivity. The mobility shows an unexpected decrease for low doping levels, as well as an unusual temperature dependence that bear resemblance with polycrystalline semiconductors

Structural Properties of Wurtzite InP–InGaAs Nanowire Core–Shell Heterostructures

We report on growth and characterization of wurtzite InP–In_1–<i>x</i>Ga_<i>x</i>As core–shell nanowire heterostructures. A range of nanowire structures with different Ga concentration in the shell was characterized with transmission electron microscopy and X-ray diffraction. We found that the main part of the nanowires has a pure wurtzite crystal structure, with occasional stacking faults occurring only at the top and bottom. This allowed us to determine the structural properties of wurtzite In_1–<i>x</i>Ga_<i>x</i>As. The InP–In_1–<i>x</i>Ga_<i>x</i>As core–shell nanowires show a triangular and hexagonal facet structure of {1100} and {101̅0} planes. X-ray diffraction measurements showed that the core and the shell are pseudomorphic along the <i>c</i>-axis, and the strained axial lattice constant is closer to the relaxed In_1–<i>x</i>Ga_<i>x</i>As shell. Microphotoluminescence measurements of the nanowires show emission in the infrared regime, which makes them suitable for applications in optical communication

Carrier Recombination Processes in Gallium Indium Phosphide Nanowires

Understanding of recombination and photoconductivity dynamics of photogenerated charge carriers in Ga_<i>x</i>In_1–xP NWs is essential for their optoelectronic applications. In this letter, we have studied a series of Ga_<i>x</i>In_1–xP NWs with varied Ga composition. Time-resolved photoinduced luminescence, femtosecond transient absorption, and time-resolved THz transmission measurements were performed to assess radiative and nonradiative recombination and photoconductivity dynamics of photogenerated charges in the NWs. We conclude that radiative recombination dynamics is limited by hole trapping, whereas electrons are highly mobile until they recombine nonradiatively. We also resolve gradual decrease of mobility of photogenerated electrons assigned to electron trapping and detrapping in a distribution of trap states. We identify that the nonradiative recombination of charges is much slower than the decay of the photoluminescence signal. Further, we conclude that trapping of both electrons and holes as well as nonradiative recombination become faster with increasing Ga composition in Ga_<i>x</i>In_1–xP NWs. We have estimated early time electron mobility in Ga_<i>x</i>In_1–xP NWs and found it to be strongly dependent on Ga composition due to the contribution of electrons in the X-valley

Fluorescent Nanowire Heterostructures as a Versatile Tool for Biology Applications

Nanowires are increasingly used in biology, as sensors, as injection devices, and as model systems for toxicity studies. Currently, in situ visualization of nanowires in biological media is done using organic dyes, which are prone to photobleaching, or using microscopy methods which either yield poor resolution or require a sophisticated setup. Here we show that inherently fluorescent nanowire axial heterostructures can be used to localize and identify nanowires in cells and tissue. By synthesizing GaP–GaInP nanowire heterostructures, with nonfluorescent GaP segments and fluorescent GaInP segments, we created a barcode labeling system enabling the distinction of the nanowire morphological and chemical properties using fluorescence microscopy. The GaInP photoluminescence stability, combined with the fact that the nanowires can be coated with different materials while retaining their fluorescence, make these nanowires promising tools for biological and nanotoxicological studies