explain this text to me “■ INTRODUCTION As potential constituent for future compact and efficient nanoscale photonic devices, semiconductor nanowires (NWs) have drawn tremendous attention in recent years.1,2 So far, a variety of nanoscale devices such as photodetectors,2−6 solar cells,7−9 lasers,10−12 and light emitting diodes (LEDs)13−15 have been devised based on semiconductor NWs. Their special one-dimensional (1D) geometry has promoted the formation of axial and radial heterostructures.16 Recently, radial core− shell NW heterostructures with excellent properties such as high carrier mobility17 and small influence from the surface states18 have attracted increasing research interest. Studies that focus on individual core−shell NW have achieved remarkably low threshold pump power densities19,20 and room-temperature lasing.19 In addition, superluminescence behavior has also been observed in the vertically aligned core−multishell NW-LED arrays.21 With the possibility of confining electronic states perpendicular to the NW axis and allowing free movements along the NW axis, the introduction of quantum wells (QWs) to the NWs with the formation of core−shell structure has evoked considerable interest,22 and related novel properties in photoelectronics have been reported.22−25 For lasers with such hybrid heterostructures, the optical cavity and gain medium can be decoupled, and the reabsorption of emission would be depressed during propagation in the NW cavity.26 Furthermore, these hybrid structures also possess obvious advantages of high-temperature stability,27 low threshold,28 and wide-range of tunable wavelength compared to the homogeneous NWs.25 III−V semiconductors with direct band gap and high carrier mobility29,30 show great potentials in photoelectronics. Among them, AlGaAs NW is an ideal substrate for radial twodimensional (2D) GaAs QWs because of their nearly perfect Received: July 4, 2019 Revised: September 21, 2019 Published: October 16, 2019 Article Cite This: J. Phys. Chem. C 2019, 123, 26888−26894 pubs.acs.org/JPCC © 2019 American Chemical Society 26888 DOI: 10.1021/acs.jpcc.9b06371 J. Phys. Chem. C 2019, 123, 26888−26894 Downloaded via BOSTON UNIV on December 2, 2019 at 04:21:47 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. lattice matching and negligible piezoelectric and strain effects.5,31 During the research of this hybrid structure, many interesting phenomena have been reported: a transition of electronic states is discovered by adjusting the width of QWs within GaAs/AlGaAs QW/NW tubes;22 further studies on optical spectroscopic measurements reveal very low excitation powers, intense emission, and extremely high quantum efficiency.23 Although this hybrid system has achieved great success in synthesis, fabrication, and various applications, little is known about corresponding band structures, and the underlying microscopic mechanisms for the observed novel optoelectronic properties also need further research. Herein, by using off-axis electron holography in combination with the first-principles calculations, the nanometer-scale electrostatic potentials and charge distributions across the GaAs/AlGaAs single QW (SQW)/NW heterostructures are quantitatively characterized, and the related band structure variations explain well the observed optoelectronic properties. This work provides insight into the inner electrical properties of III−V semiconductor NWs comprising QWs and thus is helpful for the optimization of these hybrid structures in the future.”

explain this text to me “■ INTRODUCTION As potential constituent for future compact and efficient nanoscale photonic devices, semiconductor nanowires (NWs) have drawn tremendous attention in recent years.1,2 So far, a variety of nanoscale devices such as photodetectors,2−6 solar cells,7−9 lasers,10−12 and light emitting diodes (LEDs)13−15 have been devised based on semiconductor NWs. Their special one-dimensional (1D) geometry has promoted the formation of axial and radial heterostructures.16 Recently, radial core− shell NW heterostructures with excellent properties such as high carrier mobility17 and small influence from the surface states18 have attracted increasing research interest. Studies that focus on individual core−shell NW have achieved remarkably low threshold pump power densities19,20 and room-temperature lasing.19 In addition, superluminescence behavior has also been observed in the vertically aligned core−multishell NW-LED arrays.21 With the possibility of confining electronic states perpendicular to the NW axis and allowing free movements along the NW axis, the introduction of quantum wells (QWs) to the NWs with the formation of core−shell structure has evoked considerable interest,22 and related novel properties in photoelectronics have been reported.22−25 For lasers with such hybrid heterostructures, the optical cavity and gain medium can be decoupled, and the reabsorption of emission would be depressed during propagation in the NW cavity.26 Furthermore, these hybrid structures also possess obvious advantages of high-temperature stability,27 low threshold,28 and wide-range of tunable wavelength compared to the homogeneous NWs.25 III−V semiconductors with direct band gap and high carrier mobility29,30 show great potentials in photoelectronics. Among them, AlGaAs NW is an ideal substrate for radial twodimensional (2D) GaAs QWs because of their nearly perfect Received: July 4, 2019 Revised: September 21, 2019 Published: October 16, 2019 Article Cite This: J. Phys. Chem. C 2019, 123, 26888−26894 pubs.acs.org/JPCC © 2019 American Chemical Society 26888 DOI: 10.1021/acs.jpcc.9b06371 J. Phys. Chem. C 2019, 123, 26888−26894 Downloaded via BOSTON UNIV on December 2, 2019 at 04:21:47 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. lattice matching and negligible piezoelectric and strain effects.5,31 During the research of this hybrid structure, many interesting phenomena have been reported: a transition of electronic states is discovered by adjusting the width of QWs within GaAs/AlGaAs QW/NW tubes;22 further studies on optical spectroscopic measurements reveal very low excitation powers, intense emission, and extremely high quantum efficiency.23 Although this hybrid system has achieved great success in synthesis, fabrication, and various applications, little is known about corresponding band structures, and the underlying microscopic mechanisms for the observed novel optoelectronic properties also need further research. Herein, by using off-axis electron holography in combination with the first-principles calculations, the nanometer-scale electrostatic potentials and charge distributions across the GaAs/AlGaAs single QW (SQW)/NW heterostructures are quantitatively characterized, and the related band structure variations explain well the observed optoelectronic properties. This work provides insight into the inner electrical properties of III−V semiconductor NWs comprising QWs and thus is helpful for the optimization of these hybrid structures in the future.”