Residual strain and piezoelectric effects in passivated GaAs/AlGaAs core-shell nanowires

We present a set of experimental results identifying various effects that govern the carrier dynamics of self-catalyzed GaAs/AlGaAs core-shell nanowires (NWs) grown by molecular beam epitaxy i.e. surface recombination velocity, surface charge traps, and structural defects.Time-resolved photoluminescence of NW ensemble and spatially-resolved cathodoluminescence of single NWs reveal that emission intensity, decay time and carrier diffusion length of the GaAs NW cores strongly depend on AlGaAs shell thickness but in a non-monotonic fashion. Although 7 nm-AlGaAs shell can efficiently suppress the surface recombination velocity of the GaAs NW cores, the effect of the band bending caused by the surface charges remains dominant if the shell thickness is less than 50 nm; that is, the carrier diffusion length is smaller in the NWs with a thinner shell caused by a stronger carrier scattering at the core/shell interface. If the AlGaAs shell thickness is larger than 50 nm, the luminescence efficiency of the GaAs NW cores starts to be deteriorated,

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“…2(a)]. The small red energy shift in this case is mainly caused by the residual tensile strain induced by the Al0.33Ga0.67As shell 48 .…”

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Determination of the Optimal Shell Thickness for Self-Catalyzed GaAs/AlGaAs Core–Shell Nanowires on Silicon

et al. 2016

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“…24 This discrepancy can be partly ascribed to the MetalOrganic Vapor Phase Epitaxy The small blue shift observed at low powers, which saturates around 10µW has been also observed for GaAs nanowires capped with AlGaAs shell 26,27 and it was associated with the presence of some negatively charged traps at the interface, which are filled by photo created carriers in the AlGaAs shell, which migrates towards interface. Once filled, they can no longer modify the band bending at the interface, which explains the saturation of the blue-shift of the emission energy above 10µW, indicating that the band bending is the dominant effect in our nanomembranes.…”

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confidence: 91%

“…Several effects have been reported, such as band bending at the interface leading to the accumulation of the charge at the interface or piezo electric strain. [23][24][25][26][27] In addition, the AlGaAs alloy typically used for capping GaAs nanowires is generally inhomogeneous, with directed and random segregation of Ga and Al forming respectively Al-rich ridges and Ga-rich nanoscale islands . 28,29 Simultaneously, III-V NWs can suffer from twin defects and polytypism, 30,31 which adversely affect their electronic and optical properties.…”

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“…In fact, a similar effect has been observed previously for a simple AlGaAs/GaAs interface, 23,49 InP nanowires, 50 and for GaAs nanowires capped with AlGaAs shell . 24,26,27 For simple AlGaAs/GaAs the band bending at the interface forms a pocket for the electrons or holes . 23,49 Such confined carriers at the interface will recombine with the free carriers (of the opposite species) in the valence or conduction band at a sufficient distance from the interface that flat-band conditions have been re-established.…”

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“…50 Finally, for GaAs nanowires capped with AlGaAs shell, the mechanism of the band bending can be enriched by strain, related to the shell thickness. 26,27 However, the strain plays a significant role only for rather thick shells. In the case of the nano membranes the core is much thicker than the shell.…”

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Revealing Large-Scale Homogeneity and Trace Impurity Sensitivity of GaAs Nanoscale Membranes

et al. 2017

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III-V nanostructures have the potential to revolutionize optoelectronics and energy harvesting. For this to become a reality, critical issues such as reproducibility and sensitivity to defects should be resolved. By discussing the optical properties of MBE grown GaAs nanomembranes we highlight several features that bring them closer to large scale applications. Uncapped membranes exhibit a very high optical quality, 1 arXiv:1704.08477v1 [cond-mat.mes-hall] 27 Apr 2017 expressed by extremely narrow neutral exciton emission, allowing the resolution of the more complex excitonic structure for the first time. Capping of the membranes with an AlGaAs shell results in a strong increase of emission intensity but also to a shift and broadening of the exciton peak. This is attributed to the existence of impurities in the shell, beyond MBE-grade quality, showing the high sensitivity of these structures to the presence of impurities. Finally, emission properties are identical at the sub-micron and sub-millimeter scale, demonstrating the potential of these structures for large scale applications.Keywords: GaAs/AlGaAs nano mebranes, photoluminescence, electronic and optical properties of ensemble vs single nano membrane Nanowires (NWs) are filamentary crystals with a diameter in the sub-micrometer down to nanometer range. Their special morphology, dimensions and high surface-to-volume ratio are often translated into advantageous optical and electrical properties. As a consequence, they have been widely used in electronics, 1-5 optoelectronics, 6,7 solar cells 8-11 and sensors. 12,13 If not adequately passivated, the surface recombination can limit the optical performance of the NWs. 14 In addition, surface depletion can also affect the volume distribution and separation of the carriers in the NW. 15-19 Different passivation methods have been employed in the past, notably capping of the free surfaces with a higher bandgap shell around the nanowire. [20][21][22] Nevertheless, capping also modifies the nature of the surface. Several effects have been reported, such as band bending at the interface leading to the accumulation of the charge at the interface or piezo electric strain. [23][24][25][26][27] In addition, the AlGaAs alloy typically used for capping GaAs nanowires is generally inhomogeneous, with directed and random segregation of Ga and Al forming respectively Al-rich ridges and Ga-rich nanoscale islands . 28,29 Simultaneously, III-V NWs can suffer from twin defects and polytypism, 30,31 which adversely affect their electronic and optical properties. 32-34 With a judicious optimization of growth conditions, single NWs with a pure zinc-blende or wurzite structure can be obtained. [35][36][37] Still, the optical and electronic properties tend to fluctuate considerably from NW to NW, 2 which precludes the proper control of the response of an ensemble of nanowires.Recently, alternative approaches to obtain defect-free nano structures have been proposed. Particularly promising is the inversion of polarity from B to A...

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Stress Relaxation in Nanowires with Heterostructures

Glas

2014

Wide Band Gap Semiconductor Nanowires 1

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Residual strain and piezoelectric effects in passivated GaAs/AlGaAs core-shell nanowires

Cited by 45 publications

References 30 publications

Determination of the Optimal Shell Thickness for Self-Catalyzed GaAs/AlGaAs Core–Shell Nanowires on Silicon

Determination of the Optimal Shell Thickness for Self-Catalyzed GaAs/AlGaAs Core–Shell Nanowires on Silicon

Revealing Large-Scale Homogeneity and Trace Impurity Sensitivity of GaAs Nanoscale Membranes

Stress Relaxation in Nanowires with Heterostructures

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