We have recently demonstrated that GaAs nanosheets can be grown by metal-organic chemical vapor deposition （MOCVD）. Here, we investigate these nanosheets by secondary electron scanning electron microscopy （SE-SEM）...We have recently demonstrated that GaAs nanosheets can be grown by metal-organic chemical vapor deposition （MOCVD）. Here, we investigate these nanosheets by secondary electron scanning electron microscopy （SE-SEM） and electron beam induced current （EBIC） imaging. An abrupt boundary is observed between an initial growth region and an overgrowth region in the nanosheets. The SE-SEM contrast between these two regions is attributed to the inversion of doping at the boundary. EBIC mapping reveals a p-n junction formed along the boundary between these two regions. Rectifying I-V behavior is observed across the boundary further indicating the formation of a p-n junction. The electron concentration （ND） of the initial growth region is around 1 × 10^18 cm^-3, as determined by both Hall effect measurements and low temperature photoluminescence （PL） spectroscopy. Based on the EBIC data, the minority carrier diffusion length of the nanosheets is 177 nm, which is substantially longer than the corresponding length in unpassivated GaAs nanowires measured previously.展开更多
Nanowires require surface passivation due to their inherent large surface to volume ratio. We investigate the effect of embedding InP nanowires in different oxides with respect to surface passivation by use of electro...Nanowires require surface passivation due to their inherent large surface to volume ratio. We investigate the effect of embedding InP nanowires in different oxides with respect to surface passivation by use of electron beam induced current measurements enabled by a nanoprobe based system inside a scanning electron microscope. The measurements reveal remote doping due to fixed charge carriers in the passivating PO_(x)/Al_(2)O_(3) shell in contrast to results using SiO_(x). We used time-resolved photoluminescence to characterize the lifetime of charge carriers to evaluate the success of surface passivation. In addition, spatially resolved internal quantum efficiency simulations support and correlate the two applied techniques. We find that atomic-layer deposited PO_(x)/Al_(2)O_(3) has the potential to passivate the surface of InP nanowires, but at the cost of inducing a field-effect on the nanowires, altering their electrostatic potential profile. The results show the importance of using complementary techniques to correctly evaluate and interpret processing related effects for optimization of nanowire-based optoelectronic devices.展开更多
Nanowires have many interesting properties that are of advantage for solar cells,such as the epitaxial combination of latticemismatched materials without plastic deformation.This could be utilized for the synthesis of...Nanowires have many interesting properties that are of advantage for solar cells,such as the epitaxial combination of latticemismatched materials without plastic deformation.This could be utilized for the synthesis of axial tandem-junction nanowire solar cells with high efficiency at low material cost.Electron-beam-induced current measurements have been used to optimize the performance of single-junction nanowire solar cells.Here,we use electron-beam-induced current measurements to break the barrier to photovoltaic tandem-junction nanowires.In particular,we identify and subsequently prevent the occurrence of a parasitic junction when combining an InP n-i-p junction with a tunnel diode.Furthermore,we demonstrate how to use optical and electrical biases to individually measure the electron-beam-induced current of both sub-cells of photovoltaic tandem-junction nanowires.We show that with an applied voltage in forward direction,all junctions can be analyzed simultaneously.The development of this characterization technique enables further optimization of tandem-junction nanowire solar cells.展开更多
文摘We have recently demonstrated that GaAs nanosheets can be grown by metal-organic chemical vapor deposition （MOCVD）. Here, we investigate these nanosheets by secondary electron scanning electron microscopy （SE-SEM） and electron beam induced current （EBIC） imaging. An abrupt boundary is observed between an initial growth region and an overgrowth region in the nanosheets. The SE-SEM contrast between these two regions is attributed to the inversion of doping at the boundary. EBIC mapping reveals a p-n junction formed along the boundary between these two regions. Rectifying I-V behavior is observed across the boundary further indicating the formation of a p-n junction. The electron concentration （ND） of the initial growth region is around 1 × 10^18 cm^-3, as determined by both Hall effect measurements and low temperature photoluminescence （PL） spectroscopy. Based on the EBIC data, the minority carrier diffusion length of the nanosheets is 177 nm, which is substantially longer than the corresponding length in unpassivated GaAs nanowires measured previously.
文摘Nanowires require surface passivation due to their inherent large surface to volume ratio. We investigate the effect of embedding InP nanowires in different oxides with respect to surface passivation by use of electron beam induced current measurements enabled by a nanoprobe based system inside a scanning electron microscope. The measurements reveal remote doping due to fixed charge carriers in the passivating PO_(x)/Al_(2)O_(3) shell in contrast to results using SiO_(x). We used time-resolved photoluminescence to characterize the lifetime of charge carriers to evaluate the success of surface passivation. In addition, spatially resolved internal quantum efficiency simulations support and correlate the two applied techniques. We find that atomic-layer deposited PO_(x)/Al_(2)O_(3) has the potential to passivate the surface of InP nanowires, but at the cost of inducing a field-effect on the nanowires, altering their electrostatic potential profile. The results show the importance of using complementary techniques to correctly evaluate and interpret processing related effects for optimization of nanowire-based optoelectronic devices.
基金NanoLund,Myfab,the Swedish Energy Agency,Swedish Research council,and the Knut and Alice Wallenberg Foundation(No.2016-0089).
文摘Nanowires have many interesting properties that are of advantage for solar cells,such as the epitaxial combination of latticemismatched materials without plastic deformation.This could be utilized for the synthesis of axial tandem-junction nanowire solar cells with high efficiency at low material cost.Electron-beam-induced current measurements have been used to optimize the performance of single-junction nanowire solar cells.Here,we use electron-beam-induced current measurements to break the barrier to photovoltaic tandem-junction nanowires.In particular,we identify and subsequently prevent the occurrence of a parasitic junction when combining an InP n-i-p junction with a tunnel diode.Furthermore,we demonstrate how to use optical and electrical biases to individually measure the electron-beam-induced current of both sub-cells of photovoltaic tandem-junction nanowires.We show that with an applied voltage in forward direction,all junctions can be analyzed simultaneously.The development of this characterization technique enables further optimization of tandem-junction nanowire solar cells.
