We report the first study on doping assessment in Te-doped GaAsSb nanowires (NWs) with variation ... more 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...
This study presents dual-responsive colloidal microgels to repair nonwoven fiber mats (NWFs) and ... more This study presents dual-responsive colloidal microgels to repair nonwoven fiber mats (NWFs) and recover their native morphological and functional properties. The formulation comprises poly(N-isopr...
In this work, the effects of arsenic (As) flux used during gallium (Ga) seed droplet consumption ... more In this work, the effects of arsenic (As) flux used during gallium (Ga) seed droplet consumption and the post-growth annealing on the optical, electrical, and microstructural properties of self-catalyzed molecular beam epitaxially grown tellurium (Te)-doped GaAs nanowires (NWs) have been investigated using a variety of characterization techniques. NWs using the same amount of As flux for growth of the seed droplet consumption demonstrated reduced density of stacking faults at the NW tip, with four-fold enhancement in the 4K photoluminescence (PL) intensity and increased single nanowire photocurrent over their higher As flux droplet consumption counterparts. Post-growth annealed NWs exhibited an additional low-energy PL peak at 1.31 eV that significantly reduced the overall PL intensity. The origin of this lower energy peak is assigned to a photocarrier transition from the conduction band to the annealing assisted Te-induced complex acceptor state (TeAsVGa−). In addition, post-growth...
This work reports a comprehensive investigation of the effect of gallium telluride (GaTe) cell te... more This work reports a comprehensive investigation of the effect of gallium telluride (GaTe) cell temperature variation (TGaTe) on the morphological, optical, and electrical properties of doped-GaAsSb nanowires (NWs) grown by Ga-assisted molecular beam epitaxy (MBE). These studies led to an optimum doping temperature of 550 °C for the growth of tellurium (Te)-doped GaAsSb NWs with the best optoelectronic and structural properties. Te incorporation resulted in a decrease in the aspect ratio of the NWs causing an increase in the Raman longitudinal optical/transverse optical vibrational mode intensity ratio, large photoluminescence emission with an exponential decay tail on the high energy side, promoting tunnel-assisted current conduction in ensemble NWs and significant photocurrent enhancement in the single nanowire. A Schottky barrier photodetector (PD) using Te-doped ensemble NWs with broad spectral range and a longer wavelength cutoff at ∼1.2 µm was demonstrated. These PDs exhibited ...
GaAs/GaAsSb nanowire (NW) arrays are ideally suited to meet the demands of the next generation in... more GaAs/GaAsSb nanowire (NW) arrays are ideally suited to meet the demands of the next generation infrared (IR) photodetectors with potential for improving detection. NWs in a core–shell geometry have the advantage of providing axial direction for a long optical path for enhanced optical absorption and a short radial path for charge diffusion and collection. For the Ga-assisted molecular beam epitaxial growth of vertical, dense and uniform GaAs core NWs on Si (111), the effects of substrate surface preparation in combination with growth parameter variation were examined. On the epiready substrate without any surface preparation, both initial Ga shutter opening duration and V/III beam equivalent pressure ratio play a vital role in achieving almost all vertical NWs with moderate density ~107 cm−2. Also the spatial uniformity of the NWs was poor. Substrate surface preparation by chemical cleaning followed by oxidation in air led to highly vertical and uniform NWs with high density (8 × 108 cm−2). The GaAsSb shell was then successfully grown around the highly dense and vertical core GaAs NWs at growth temperatures ranging from 550°C to 590°C. It was found that growth temperature has a strong influence on Sb incorporation in the NWs and, hence, the NW morphology and 4K photoluminescence (PL) spectra. The presence of x-ray diffraction peaks corresponding to (111) reflection only and its higher-order reflections attest to the vertical alignment of NWs. Strain in the NWs as estimated using the Williamson–Hall isotropic strain model increases with Sb incorporation, which results in bending of the NWs with increasing Sb. Structural properties of these NWs using scanning transmission electron microscopy (STEM) are also presented. The temperature dependence PL of the NWs exhibited “S-curve” behavior, which is a well-known signature of localized excitons and a room temperature band edge PL emission occurring at ~1.3 μm.
ABSTRACT Ga assisted GaAs/GaAsSb core-shell structured nanowires were successfully grown on chemi... more ABSTRACT Ga assisted GaAs/GaAsSb core-shell structured nanowires were successfully grown on chemically etched p-type Si(111) substrate by molecular beam epitaxy (MBE). The morphology, structural and optical properties of the nanowires are found to be strongly influenced by the shell growth temperature and Sb% in the nanowires. The nanowires exhibit planar defects like twins and stacking faults, with more stacking faults and micro-twins found at the top section. Optical characteristics of the nanowires as measured by 4K photoluminescence (PL) exhibit a red shift to 1.2 eV with increasing Sb incorporation up to 12%. The Raman spectra of reference GaAs nanowires show TO and LO modes representative of the zinc blende structure at 291 cm-1 and 267.8 cm-1 , respectively. Red shifts of both modes in conjunction with corresponding asymmetrical peak broadening observed in X-ray diffraction with increasing Sb incorporation are attributed to enhanced strain and disorder within the nanostructures. Nanowires of similar Sb composition but grown at different shell temperatures reveal straight nanowires with better microstructural and optical quality when grown at higher growth temperatures. The presence of GaAs passivation layer significantly enhanced the PL intensity such that PL was observed even at room temperature.
Electro-absorption modulated sources are likely to be key components in the evolution of optical ... more Electro-absorption modulated sources are likely to be key components in the evolution of optical communication line rates from 10Gb/s to 40 Gb/s. Compared with the LiNbO<SUB>3</SUB> alternative EA.
We have investigated three In1-xGaxAsyP1-y/InP p-i-n multiple quantum well (MQW) laser structures... more We have investigated three In1-xGaxAsyP1-y/InP p-i-n multiple quantum well (MQW) laser structures with different p-doping profiles using contactless electroreflectance (CER) and piezoreflectance (PZR). From the observed Franz-Keldysh oscillations originating in the i-InGaAsP regions, we have evaluated the electric field and hence the amount of p-dopant interdiffusion, which is in agreement with secondary ion mass spectrometry measurements. The CER/PZR spectra from
In this work, we report on the p-i GaAsSb/AlGaAs nanowires (NWs) ensemble device exhibiting good ... more In this work, we report on the p-i GaAsSb/AlGaAs nanowires (NWs) ensemble device exhibiting good spectral response up to 1.1 µm with a high responsivity of 311 A/W, an external quantum efficiency of 6.1x104 %, and a detectivity of 1.9x1010 Jones at 633 nm. The high responsivity of the NWs has been attributed to in-situ post-growth annealing of GaAsSb axial NWs in the ultra-high vacuum. The enabling growth technology is molecular beam epitaxy for the Ga-assisted epitaxial growth of these NWs on Si (111) substrates. Room temperature Raman spectra, as well as temperature dependent micro-photoluminescence (μ-PL) peak analysis indicated suppression of band tail states and non-radiative channels due to annealing. A similar improvement in in-situ annealed p-i GaAsSb NW ensemble with an AlGaAs passivating shell was inferred from a reduction in the Schottky barrier height as well as the NW resistance compared to the as-grown NW ensemble. These results demonstrate in-situ annealing of nanowir...
Intrinsic and Te-doped GaAsSb nanowires with diameters ~100–120 nm were grown on a p-type Si(111)... more Intrinsic and Te-doped GaAsSb nanowires with diameters ~100–120 nm were grown on a p-type Si(111) substrate by molecular beam epitaxy (MBE). Detailed magnetic, current/voltage and low-energy electron energy loss spectroscopy measurements were performed to investigate the effect of Te-doping. While intrinsic nanowires are diamagnetic over the temperature range 5–300 K, the Te-doped nanowires exhibit ferromagnetic behavior with the easy axis of magnetism perpendicular to the longitudinal axis of the nanowire. The temperature dependence of coercivity was analyzed and shown to be in agreement with a thermal activation model from 50–350 K but reveal more complex behavior in the low temperature regime. The EELS data show that Te doping introduced a high density of states (DOS) in the nanowire above the Fermi level in close proximity to the conduction band. The plausible origin of ferromagnetism in these Te-doped GaAsSb nanowires is discussed on the basis of d0 ferromagnetism, spin orderin...
We report the first study on doping assessment in Te-doped GaAsSb nanowires (NWs) with variation ... more 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...
This study presents dual-responsive colloidal microgels to repair nonwoven fiber mats (NWFs) and ... more This study presents dual-responsive colloidal microgels to repair nonwoven fiber mats (NWFs) and recover their native morphological and functional properties. The formulation comprises poly(N-isopr...
In this work, the effects of arsenic (As) flux used during gallium (Ga) seed droplet consumption ... more In this work, the effects of arsenic (As) flux used during gallium (Ga) seed droplet consumption and the post-growth annealing on the optical, electrical, and microstructural properties of self-catalyzed molecular beam epitaxially grown tellurium (Te)-doped GaAs nanowires (NWs) have been investigated using a variety of characterization techniques. NWs using the same amount of As flux for growth of the seed droplet consumption demonstrated reduced density of stacking faults at the NW tip, with four-fold enhancement in the 4K photoluminescence (PL) intensity and increased single nanowire photocurrent over their higher As flux droplet consumption counterparts. Post-growth annealed NWs exhibited an additional low-energy PL peak at 1.31 eV that significantly reduced the overall PL intensity. The origin of this lower energy peak is assigned to a photocarrier transition from the conduction band to the annealing assisted Te-induced complex acceptor state (TeAsVGa−). In addition, post-growth...
This work reports a comprehensive investigation of the effect of gallium telluride (GaTe) cell te... more This work reports a comprehensive investigation of the effect of gallium telluride (GaTe) cell temperature variation (TGaTe) on the morphological, optical, and electrical properties of doped-GaAsSb nanowires (NWs) grown by Ga-assisted molecular beam epitaxy (MBE). These studies led to an optimum doping temperature of 550 °C for the growth of tellurium (Te)-doped GaAsSb NWs with the best optoelectronic and structural properties. Te incorporation resulted in a decrease in the aspect ratio of the NWs causing an increase in the Raman longitudinal optical/transverse optical vibrational mode intensity ratio, large photoluminescence emission with an exponential decay tail on the high energy side, promoting tunnel-assisted current conduction in ensemble NWs and significant photocurrent enhancement in the single nanowire. A Schottky barrier photodetector (PD) using Te-doped ensemble NWs with broad spectral range and a longer wavelength cutoff at ∼1.2 µm was demonstrated. These PDs exhibited ...
GaAs/GaAsSb nanowire (NW) arrays are ideally suited to meet the demands of the next generation in... more GaAs/GaAsSb nanowire (NW) arrays are ideally suited to meet the demands of the next generation infrared (IR) photodetectors with potential for improving detection. NWs in a core–shell geometry have the advantage of providing axial direction for a long optical path for enhanced optical absorption and a short radial path for charge diffusion and collection. For the Ga-assisted molecular beam epitaxial growth of vertical, dense and uniform GaAs core NWs on Si (111), the effects of substrate surface preparation in combination with growth parameter variation were examined. On the epiready substrate without any surface preparation, both initial Ga shutter opening duration and V/III beam equivalent pressure ratio play a vital role in achieving almost all vertical NWs with moderate density ~107 cm−2. Also the spatial uniformity of the NWs was poor. Substrate surface preparation by chemical cleaning followed by oxidation in air led to highly vertical and uniform NWs with high density (8 × 108 cm−2). The GaAsSb shell was then successfully grown around the highly dense and vertical core GaAs NWs at growth temperatures ranging from 550°C to 590°C. It was found that growth temperature has a strong influence on Sb incorporation in the NWs and, hence, the NW morphology and 4K photoluminescence (PL) spectra. The presence of x-ray diffraction peaks corresponding to (111) reflection only and its higher-order reflections attest to the vertical alignment of NWs. Strain in the NWs as estimated using the Williamson–Hall isotropic strain model increases with Sb incorporation, which results in bending of the NWs with increasing Sb. Structural properties of these NWs using scanning transmission electron microscopy (STEM) are also presented. The temperature dependence PL of the NWs exhibited “S-curve” behavior, which is a well-known signature of localized excitons and a room temperature band edge PL emission occurring at ~1.3 μm.
ABSTRACT Ga assisted GaAs/GaAsSb core-shell structured nanowires were successfully grown on chemi... more ABSTRACT Ga assisted GaAs/GaAsSb core-shell structured nanowires were successfully grown on chemically etched p-type Si(111) substrate by molecular beam epitaxy (MBE). The morphology, structural and optical properties of the nanowires are found to be strongly influenced by the shell growth temperature and Sb% in the nanowires. The nanowires exhibit planar defects like twins and stacking faults, with more stacking faults and micro-twins found at the top section. Optical characteristics of the nanowires as measured by 4K photoluminescence (PL) exhibit a red shift to 1.2 eV with increasing Sb incorporation up to 12%. The Raman spectra of reference GaAs nanowires show TO and LO modes representative of the zinc blende structure at 291 cm-1 and 267.8 cm-1 , respectively. Red shifts of both modes in conjunction with corresponding asymmetrical peak broadening observed in X-ray diffraction with increasing Sb incorporation are attributed to enhanced strain and disorder within the nanostructures. Nanowires of similar Sb composition but grown at different shell temperatures reveal straight nanowires with better microstructural and optical quality when grown at higher growth temperatures. The presence of GaAs passivation layer significantly enhanced the PL intensity such that PL was observed even at room temperature.
Electro-absorption modulated sources are likely to be key components in the evolution of optical ... more Electro-absorption modulated sources are likely to be key components in the evolution of optical communication line rates from 10Gb/s to 40 Gb/s. Compared with the LiNbO<SUB>3</SUB> alternative EA.
We have investigated three In1-xGaxAsyP1-y/InP p-i-n multiple quantum well (MQW) laser structures... more We have investigated three In1-xGaxAsyP1-y/InP p-i-n multiple quantum well (MQW) laser structures with different p-doping profiles using contactless electroreflectance (CER) and piezoreflectance (PZR). From the observed Franz-Keldysh oscillations originating in the i-InGaAsP regions, we have evaluated the electric field and hence the amount of p-dopant interdiffusion, which is in agreement with secondary ion mass spectrometry measurements. The CER/PZR spectra from
In this work, we report on the p-i GaAsSb/AlGaAs nanowires (NWs) ensemble device exhibiting good ... more In this work, we report on the p-i GaAsSb/AlGaAs nanowires (NWs) ensemble device exhibiting good spectral response up to 1.1 µm with a high responsivity of 311 A/W, an external quantum efficiency of 6.1x104 %, and a detectivity of 1.9x1010 Jones at 633 nm. The high responsivity of the NWs has been attributed to in-situ post-growth annealing of GaAsSb axial NWs in the ultra-high vacuum. The enabling growth technology is molecular beam epitaxy for the Ga-assisted epitaxial growth of these NWs on Si (111) substrates. Room temperature Raman spectra, as well as temperature dependent micro-photoluminescence (μ-PL) peak analysis indicated suppression of band tail states and non-radiative channels due to annealing. A similar improvement in in-situ annealed p-i GaAsSb NW ensemble with an AlGaAs passivating shell was inferred from a reduction in the Schottky barrier height as well as the NW resistance compared to the as-grown NW ensemble. These results demonstrate in-situ annealing of nanowir...
Intrinsic and Te-doped GaAsSb nanowires with diameters ~100–120 nm were grown on a p-type Si(111)... more Intrinsic and Te-doped GaAsSb nanowires with diameters ~100–120 nm were grown on a p-type Si(111) substrate by molecular beam epitaxy (MBE). Detailed magnetic, current/voltage and low-energy electron energy loss spectroscopy measurements were performed to investigate the effect of Te-doping. While intrinsic nanowires are diamagnetic over the temperature range 5–300 K, the Te-doped nanowires exhibit ferromagnetic behavior with the easy axis of magnetism perpendicular to the longitudinal axis of the nanowire. The temperature dependence of coercivity was analyzed and shown to be in agreement with a thermal activation model from 50–350 K but reveal more complex behavior in the low temperature regime. The EELS data show that Te doping introduced a high density of states (DOS) in the nanowire above the Fermi level in close proximity to the conduction band. The plausible origin of ferromagnetism in these Te-doped GaAsSb nanowires is discussed on the basis of d0 ferromagnetism, spin orderin...
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