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

Abstract

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...

Growth kinetics and morphological analysis of homoepitaxial GaAs fins by theory and experiment

“…By extending the slits in the <11-2> direction up to several microns, vertical nanomembranes (NMs) are obtained, as reported in the literature for both MOCVD 4,5 and Molecular Beam Epitaxy (MBE) 6 . These NMs have shown to exhibit exceptional optical properties, as a consequence of their perfect crystal structure and absence of twinning defects 7 , a feature that prevents also the occurrence of twinning-driven tilting, as in the case of nanowires 8 . In addition, it was recently demonstrated that these NMs can act as templates for the growth of horizontally aligned InAs nanowires 9 .…”

Optical properties and carrier dynamics in Co-doped ZnO nanorods

“…40 Similar CL emissions due to oxygen vacancies were observed in ZnO doped with IIIa elements as donors or with Li as an acceptor by Ohashi et al 41 One should note here that the optical properties of high quality semiconductors are sensitive to very low densities of defects/doping. 42 Other reports have shown that surface defects, especially oxygen vacancies, play a very important role in photocatalytic activity, especially in the efficiency of ZnO as a PEC material. [43][44][45] This is attributed to the enhanced absorption of visible light and increased carrier trapping associated with the increased defect states.…”

GaAs nanoscale membranes: prospects for seamless integration of III–Vs on silicon

“…The FWHM is quite broad, especially compared to the values obtained in homoepitaxial GaAs NMs, which is narrower by approximately one order of magnitude. 41,43 This broadening is attributed to the presence of twinning defects, as confirmed by transmission electron microscopy (TEM) measurements.…”

“…46 Low-temperature CL and μ-PL spectroscopy was performed to characterize their optical properties. While the luminescence of GaAs nanoscale membranes on GaAs substrates is consistent with their absolute defect-free nature, 43 the lumine-scence of GaAs nanoscale membranes on Si exhibits a richer structure. We show the results on these two structures, which are consistent with measurements on the rest of the membranes of the array.…”

“…42 They exhibit a defect-free crystal structure which leads to a high homogeneity in the optical properties of NM ensembles. 43 Their high aspect-ratio geometry combined with their pristine crystal quality enables their use as templates for growing highly mismatched materials, 44 extending their functionality and design opportunities. 45 In the present study, our particular interest is in exploring how GaAs NMs can be used to address some of the major challenges associated with integrating III-Vs on silicon substrates.…”