This study presents the first report on patterned nanowires (NWs) of dilute nitride GaAsSbN on p-Si (111) substrates by self-catalyzed plasma-assisted molecular beam epitaxy. Patterned NW array with GaAsSbN of Sb composition of 3% as a stem provided the best yield of vertical NWs. Large bandgap tuning of ~ 75 meV, as ascertained from 4 K photoluminescence (PL), over a pitch length variation of 200–1200 nm has been demonstrated. Pitch-dependent axial and radial growth rates show a logistic sigmoidal growth trend different from those commonly observed in other patterned non-nitride III–V NWs. The sigmoidal fitting provides further insight into the PL spectral shift arising from differences in Sb and N incorporation from pitch induced variation in secondary fluxes. Results indicate that sigmoidal fitting can be a potent tool for designing patterned NW arrays of optimal pitch length for dilute nitrides and other highly mismatched alloys and heterostructures.
Revealing charge carrier dynamics and transport in Te-doped GaAsSb and GaAsSbN nanowires by correlating ultrafast terahertz spectroscopy and optoelectronic characterization
Abstract Recent advances in the growth of III-V semiconductor nanowires (NWs) hold great promise for nanoscale optoelectronic device applications. Recently, it was found 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.
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- Award ID(s):
- 1832117
- NSF-PAR ID:
- 10339262
- Editor(s):
- LaPierre, Ray
- Date Published:
- Journal Name:
- Nanotechnology
- ISSN:
- 0957-4484
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract This work evaluates the passivation efficacy of thermal atomic layer deposited (ALD) Al 2 O 3 dielectric layer on self-catalyzed GaAs 1- x Sb x nanowires (NWs) grown using molecular beam epitaxy. A detailed assessment of surface chemical composition and optical properties of Al 2 O 3 passivated NWs with and without prior sulfur treatment were studied and compared to as-grown samples using x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and low-temperature photoluminescence (PL) spectroscopy. The XPS measurements reveal that prior sulfur treatment followed by Al 2 O 3 ALD deposition abates III–V native oxides from the NW surface. However, the degradation in 4K-PL intensity by an order of magnitude observed for NWs with Al 2 O 3 shell layer compared to the as-grown NWs, irrespective of prior sulfur treatment, suggests the formation of defect states at the NW/dielectric interface contributing to non-radiative recombination centers. This is corroborated by the Raman spectral broadening of LO and TO Raman modes, increased background scattering, and redshift observed for Al 2 O 3 deposited NWs relative to the as-grown. Thus, our work seems to indicate the unsuitability of ALD deposited Al 2 O 3 as a passivation layer for GaAsSb NWs.more » « less
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null (Ed.)We report the first study on doping assessment in Te-doped GaAsSb nanowires (NWs) with variation in Gallium Telluride (GaTe) cell temperature, using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), conductive-atomic force microscopy (C-AFM), and scanning Kelvin probe microscopy (SKPM). The NWs were grown using Ga-assisted molecular beam epitaxy with a GaTe captive source as the dopant cell. Te-incorporation in the NWs was associated with a positive shift in the binding energy of the 3d shells of the core constituent elements in doped NWs in the XPS spectra, a lowering of the work function in doped NWs relative to undoped ones from UPS spectra, a significantly higher photoresponse in C-AFM and an increase in surface potential of doped NWs observed in SKPM relative to undoped ones. The carrier concentration of Te-doped GaAsSb NWs determined from UPS spectra are found to be consistent with the values obtained from simulated I-V characteristics. Thus, these surface analytical tools, XPS/UPS and C-AFM/SKPM, that do not require any sample preparation are found to be powerful characterization techniques to analyze the dopant incorporation and carrier density in homogeneously doped NWs.more » « less
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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.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/1361-6528/ac7d61
