Miniaturization of light-emitting diodes(LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definiti...Miniaturization of light-emitting diodes(LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definition televisions,augmented/mixed realities and head-up displays, and also on optogenetics, high-speed light communication, etc. The conventional top-down technology uses dry etching to define the LED size, leading to damage to the LED side walls.Since sizes of microLEDs approach the carrier diffusion length, the damaged side walls play an important role, reducing microLED performance significantly from that of large area LEDs. In this paper, we review our efforts on realization of microLEDs by direct bottom-up growth, based on selective area metal–organic vapor phase epitaxy. The individual LEDs based on either GaN nanowires or InGaN platelets are smaller than 1 μm in our approach. Such nano-LEDs can be used as building blocks in arrays to assemble microLEDs with different sizes, avoiding the side wall damage by dry etching encountered for the top-down approach. The technology of InGaN platelets is especially interesting since InGaN quantum wells emitting red, green and blue light can be grown on such platelets with a low-level of strain by changing the indium content in the InGaN platelets. This technology is therefore very attractive for highly efficient microLEDs of three primary colors for displays.展开更多
We report a method using in situ etching to decouple the axial from the radial nanowire growth pathway,independent of other growth parameters.Thereby a wide range of growth parameters can be explored to improve the na...We report a method using in situ etching to decouple the axial from the radial nanowire growth pathway,independent of other growth parameters.Thereby a wide range of growth parameters can be explored to improve the nanowire properties without concern of tapering or excess structural defects formed during radial growth.We demonstrate the method using etching by HCl during InP nanowire growth.The improved crystal quality of etched nanowires is indicated by strongly enhanced photoluminescence as compared to reference nanowires obtained without etching.展开更多
An understanding of the absorption of light is essential for efficient photovoltaic and photodetection applications with III-V nanowire arrays. Here, we correlate experiments with modeling and verify experimentally th...An understanding of the absorption of light is essential for efficient photovoltaic and photodetection applications with III-V nanowire arrays. Here, we correlate experiments with modeling and verify experimentally the predicted absorption of light in InP nanowire arrays for varying nanowire diameter and length. We find that 2,000 nm long nanowires in a pitch of 400 nm can absorb 94% of the incident light with energy above the band gap and, as a consequence, light which in a simple ray-optics description would be travelling between the nanowires can be efficiently absorbed by the nanowires. Our measurements demonstrate that the absorption for long nanowires is limited by insertion reflection losses when light is coupled from the air top-region into the array. These reflection losses can be reduced by introducing a smaller diameter to the nanowire-part closest to the air top-region. For nanowire arrays with such a nanowire morphology modulation, we find that the absorptance increases monotonously with increasing diameter of the rest of the nanowire.展开更多
Live observations of growing nanowires using in situ transmission electron microscopy （TEM） is becoming an increasingly important tool for understanding the dynamic processes occurring during nanowire growth. Here w...Live observations of growing nanowires using in situ transmission electron microscopy （TEM） is becoming an increasingly important tool for understanding the dynamic processes occurring during nanowire growth. Here we present observations of growing InAs nanowires, which constitute the first reported in situ growth of a In-V compound in a transmission electron microscope. Real time observations of events taking place over longer growth lengths were possible due to the high growth rates of up to I nm/s that were achieved. Straight growth （mainly in 〈111〉B directions） was observed at uniform temperature and partial pressure while intentional fluctuations in these conditions caused the nanowires to form kinks and change growth direction. The mechanisms behind the kinking are discussed in detail. In situ observations of nanowire kinking has previously only been reported for nonpolar diamond structure type materials （such as Si）, but here we present results for a polar zinc blende structure （InAs）. In this study a closed cell with electron and X-ray transparent a-SiN windows was used in a conventional high resolution transmission electron microscope, enabling high resolution imaging and compositional analysis in between the growth periods.展开更多
Aerosol technology provides efficient methods for producing nanoparticles with well-controlled composition and size distribution. This review provides an overview of methods and results obtained by using aerosol techn...Aerosol technology provides efficient methods for producing nanoparticles with well-controlled composition and size distribution. This review provides an overview of methods and results obtained by using aerosol technology for producing nanostruetures for a variety of applications in semiconductor physics and device technology. Examples are given from： production of metal and metal alloy particles： semiconductor nanoparticles; semiconductor nanowires, grown both in the aerosol phase and on substrates; physics studies based on individual aerosol-generated devices; and large area deviees based on aerosol particles.展开更多
We have investigated individual bulk-like wires of wurtzite InP using photoluminescence, photoluminescence excitation spectroscopy and transmission electron microscopy. Using two different methods we find that the top...We have investigated individual bulk-like wires of wurtzite InP using photoluminescence, photoluminescence excitation spectroscopy and transmission electron microscopy. Using two different methods we find that the top of the valence band is split, as expected theoretically. This splitting of the valence band is peculiar to wurtzite InP and does not occur in zinc blende InP. We find the energy difference between the two bands to be 40 meV.展开更多
In-air epitaxy of nanostructures(Aerotaxy)has recently emerged as a viable route for fast,large-scale production.In this study,we use small-a ngle X-ray scatteri ng to perform direct in-flight characterizati ons of th...In-air epitaxy of nanostructures(Aerotaxy)has recently emerged as a viable route for fast,large-scale production.In this study,we use small-a ngle X-ray scatteri ng to perform direct in-flight characterizati ons of the first step of this process,i.e.,the en gineered formatio n of Au and Pt aerosol nan oparticles by spark gen erati on in a flow of N2 gas.This represe nts a particular challe nge for characterizati on because the particle density can be extremely low in con trolled production.The particles produced are exami ned duri ng producti on at operatio nal pressures close to atmospheric conditions and exhibit a log no rmal size distributi on ranging from 5-100nm.The Au and Pt particle productio n and detection are compared.We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding domi nant physical properties,in cludi ng the average particle diameter and sphericity,as in flue need by particle sintering and the prese nee of aggregates.We observe highly sorted and sin tered spherical Au nano particles at ultra-dilute concen tratio ns(<5×10^5 particles/cm^3)corresponding to a volume fraction below 3×10^-10,which is orders of magnitude below that of previously measured aerosols.We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis.Our study indicates that with high-intensity synchrotron beams and careful con sideratio n of backgro und removal,size and shape info rmati on can be obtai ned for extremely low particle concentrations with industrially relevant narrow size distributions.展开更多
In this report we explore the structural and optical properties of GaAs/A1GaAs heterostructure nanowires grown by metalorganic vapour phase epitaxy using gold seed-particles. The optical studies were done by low-tempe...In this report we explore the structural and optical properties of GaAs/A1GaAs heterostructure nanowires grown by metalorganic vapour phase epitaxy using gold seed-particles. The optical studies were done by low-temperature cathodo- luminescence （CL） in a scanning electron microscope （SEM）. We perform a systematic investigation of how the nanowire growth-temperature affects the total photon emission, and variations in the emission energy and intensity along the length of the nanowires. The morphology and crystal structures of the nanowires were investigated using SEM and transmission electron microscopy （TEM）. In order to correlate specific photon emission characteristics with variations in the nanowire crystal structure directly, TEM and spatially resolved CL measurements were performed on the same individual nanowires. We found that the main emission energy was located at around 1.48 eV, and that the emission intensity was greatly enhanced when increasing the GaAs nanowire core growth temperature. The data strongly suggests that this emission energy is related to rotational twins in the GaAs nanowire core. Our measurements also show that radial overgrowth by GaAs on the GaAs nanowire core can have a deteriorating effect on the optical quality of the nanowires. Finally, we conclude that an in situ pre-growth annealing step at a sufficiently high temperature significantly improves the optical quality of the nanowires.展开更多
We report on electrical and optical properties of p＋-i-n＋ photodetectors/solar cells based on square millimeter arrays of InP nanowires （NWs） grown on InP substrates. The study includes a sample series where the p...We report on electrical and optical properties of p＋-i-n＋ photodetectors/solar cells based on square millimeter arrays of InP nanowires （NWs） grown on InP substrates. The study includes a sample series where the p＋-segment length was varied between 0 and 250 nm, as well as solar cells with 9.3% efficiency with similar design. The electrical data for all devices display clear rectifying behavior with an ideality factor between 1.8 and 2.5 at 300 K. From spectrally resolved photocurrent measurements, we conclude that the photocurrent generation process depends strongly on the p^-segment length. Without a p＋-segment, photogenerated carriers funneled from the substrate into the NWs contribute strongly to the photocurrent. Adding a p＋-segment decouples the substrate and shifts the depletion region, and collection of photogenerated carriers, to the NWs, in agreement with theoretical modeling. In optimized solar cells, clear spectral signatures of interband transitions in the zinc blende and wurtzite InP layers of the mixed-phase i-segments are observed. Complementary electroluminescence, transmission electron microscopy （TEM）, as well as measurements of the dependence of the photocurrent on angle of incidence and polarization, support our interpretations.展开更多
Realizing photon upconversion in nanostructures is important for many next- generation applications such as biological labelling, infrared detectors and solar cells. In particular nanowires are attractive for optoelec...Realizing photon upconversion in nanostructures is important for many next- generation applications such as biological labelling, infrared detectors and solar cells. In particular nanowires are attractive for optoelectronics because they can easily be electrically contacted. Here we demonstrate photon upconversion with a large energy shift in highly n-doped InP nanowires. Crucially, the mechanism responsible for the upconversion in our system does not rely on multi-photon absorption via intermediate states, thus eliminating the need for high photon fluxes to achieve upconversion. The demonstrated upconversion paves the way for utilizing nanowires--with their inherent flexibility such as electrical contactability and the ability to position individual nanowires--for photon upconversion devices also at low photon fluxes, possibly down to the single photon level in optimised structures.展开更多
基金supported by the Swedish Research Council (VR),the Foundation for Strategic Research (SSF),the Knut and Alice Wallenberg foundation (KAW),the Swedish Energy Agency and Sweden’s innovation agency (VINNOVA)。
文摘Miniaturization of light-emitting diodes(LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definition televisions,augmented/mixed realities and head-up displays, and also on optogenetics, high-speed light communication, etc. The conventional top-down technology uses dry etching to define the LED size, leading to damage to the LED side walls.Since sizes of microLEDs approach the carrier diffusion length, the damaged side walls play an important role, reducing microLED performance significantly from that of large area LEDs. In this paper, we review our efforts on realization of microLEDs by direct bottom-up growth, based on selective area metal–organic vapor phase epitaxy. The individual LEDs based on either GaN nanowires or InGaN platelets are smaller than 1 μm in our approach. Such nano-LEDs can be used as building blocks in arrays to assemble microLEDs with different sizes, avoiding the side wall damage by dry etching encountered for the top-down approach. The technology of InGaN platelets is especially interesting since InGaN quantum wells emitting red, green and blue light can be grown on such platelets with a low-level of strain by changing the indium content in the InGaN platelets. This technology is therefore very attractive for highly efficient microLEDs of three primary colors for displays.
基金This work was performed within the Nanometer Structure Consortium at Lund University and supported by the Swedish Energy Agency,the Swedish Research Council,the Swedish Foundation for Strategic Research,and by the EU programs AMON-RA(No.214814)and NODE(No.015783)This report is based on a project which was funded by E.ON AG as part of the E.ON International Research Initiative.Responsibility for the content of this publication lies with the authors.
文摘We report a method using in situ etching to decouple the axial from the radial nanowire growth pathway,independent of other growth parameters.Thereby a wide range of growth parameters can be explored to improve the nanowire properties without concern of tapering or excess structural defects formed during radial growth.We demonstrate the method using etching by HCl during InP nanowire growth.The improved crystal quality of etched nanowires is indicated by strongly enhanced photoluminescence as compared to reference nanowires obtained without etching.
文摘An understanding of the absorption of light is essential for efficient photovoltaic and photodetection applications with III-V nanowire arrays. Here, we correlate experiments with modeling and verify experimentally the predicted absorption of light in InP nanowire arrays for varying nanowire diameter and length. We find that 2,000 nm long nanowires in a pitch of 400 nm can absorb 94% of the incident light with energy above the band gap and, as a consequence, light which in a simple ray-optics description would be travelling between the nanowires can be efficiently absorbed by the nanowires. Our measurements demonstrate that the absorption for long nanowires is limited by insertion reflection losses when light is coupled from the air top-region into the array. These reflection losses can be reduced by introducing a smaller diameter to the nanowire-part closest to the air top-region. For nanowire arrays with such a nanowire morphology modulation, we find that the absorptance increases monotonously with increasing diameter of the rest of the nanowire.
文摘Live observations of growing nanowires using in situ transmission electron microscopy （TEM） is becoming an increasingly important tool for understanding the dynamic processes occurring during nanowire growth. Here we present observations of growing InAs nanowires, which constitute the first reported in situ growth of a In-V compound in a transmission electron microscope. Real time observations of events taking place over longer growth lengths were possible due to the high growth rates of up to I nm/s that were achieved. Straight growth （mainly in 〈111〉B directions） was observed at uniform temperature and partial pressure while intentional fluctuations in these conditions caused the nanowires to form kinks and change growth direction. The mechanisms behind the kinking are discussed in detail. In situ observations of nanowire kinking has previously only been reported for nonpolar diamond structure type materials （such as Si）, but here we present results for a polar zinc blende structure （InAs）. In this study a closed cell with electron and X-ray transparent a-SiN windows was used in a conventional high resolution transmission electron microscope, enabling high resolution imaging and compositional analysis in between the growth periods.
文摘Aerosol technology provides efficient methods for producing nanoparticles with well-controlled composition and size distribution. This review provides an overview of methods and results obtained by using aerosol technology for producing nanostruetures for a variety of applications in semiconductor physics and device technology. Examples are given from： production of metal and metal alloy particles： semiconductor nanoparticles; semiconductor nanowires, grown both in the aerosol phase and on substrates; physics studies based on individual aerosol-generated devices; and large area deviees based on aerosol particles.
文摘We have investigated individual bulk-like wires of wurtzite InP using photoluminescence, photoluminescence excitation spectroscopy and transmission electron microscopy. Using two different methods we find that the top of the valence band is split, as expected theoretically. This splitting of the valence band is peculiar to wurtzite InP and does not occur in zinc blende InP. We find the energy difference between the two bands to be 40 meV.
文摘In-air epitaxy of nanostructures(Aerotaxy)has recently emerged as a viable route for fast,large-scale production.In this study,we use small-a ngle X-ray scatteri ng to perform direct in-flight characterizati ons of the first step of this process,i.e.,the en gineered formatio n of Au and Pt aerosol nan oparticles by spark gen erati on in a flow of N2 gas.This represe nts a particular challe nge for characterizati on because the particle density can be extremely low in con trolled production.The particles produced are exami ned duri ng producti on at operatio nal pressures close to atmospheric conditions and exhibit a log no rmal size distributi on ranging from 5-100nm.The Au and Pt particle productio n and detection are compared.We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding domi nant physical properties,in cludi ng the average particle diameter and sphericity,as in flue need by particle sintering and the prese nee of aggregates.We observe highly sorted and sin tered spherical Au nano particles at ultra-dilute concen tratio ns(<5×10^5 particles/cm^3)corresponding to a volume fraction below 3×10^-10,which is orders of magnitude below that of previously measured aerosols.We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis.Our study indicates that with high-intensity synchrotron beams and careful con sideratio n of backgro und removal,size and shape info rmati on can be obtai ned for extremely low particle concentrations with industrially relevant narrow size distributions.
文摘In this report we explore the structural and optical properties of GaAs/A1GaAs heterostructure nanowires grown by metalorganic vapour phase epitaxy using gold seed-particles. The optical studies were done by low-temperature cathodo- luminescence （CL） in a scanning electron microscope （SEM）. We perform a systematic investigation of how the nanowire growth-temperature affects the total photon emission, and variations in the emission energy and intensity along the length of the nanowires. The morphology and crystal structures of the nanowires were investigated using SEM and transmission electron microscopy （TEM）. In order to correlate specific photon emission characteristics with variations in the nanowire crystal structure directly, TEM and spatially resolved CL measurements were performed on the same individual nanowires. We found that the main emission energy was located at around 1.48 eV, and that the emission intensity was greatly enhanced when increasing the GaAs nanowire core growth temperature. The data strongly suggests that this emission energy is related to rotational twins in the GaAs nanowire core. Our measurements also show that radial overgrowth by GaAs on the GaAs nanowire core can have a deteriorating effect on the optical quality of the nanowires. Finally, we conclude that an in situ pre-growth annealing step at a sufficiently high temperature significantly improves the optical quality of the nanowires.
文摘We report on electrical and optical properties of p＋-i-n＋ photodetectors/solar cells based on square millimeter arrays of InP nanowires （NWs） grown on InP substrates. The study includes a sample series where the p＋-segment length was varied between 0 and 250 nm, as well as solar cells with 9.3% efficiency with similar design. The electrical data for all devices display clear rectifying behavior with an ideality factor between 1.8 and 2.5 at 300 K. From spectrally resolved photocurrent measurements, we conclude that the photocurrent generation process depends strongly on the p^-segment length. Without a p＋-segment, photogenerated carriers funneled from the substrate into the NWs contribute strongly to the photocurrent. Adding a p＋-segment decouples the substrate and shifts the depletion region, and collection of photogenerated carriers, to the NWs, in agreement with theoretical modeling. In optimized solar cells, clear spectral signatures of interband transitions in the zinc blende and wurtzite InP layers of the mixed-phase i-segments are observed. Complementary electroluminescence, transmission electron microscopy （TEM）, as well as measurements of the dependence of the photocurrent on angle of incidence and polarization, support our interpretations.
文摘Realizing photon upconversion in nanostructures is important for many next- generation applications such as biological labelling, infrared detectors and solar cells. In particular nanowires are attractive for optoelectronics because they can easily be electrically contacted. Here we demonstrate photon upconversion with a large energy shift in highly n-doped InP nanowires. Crucially, the mechanism responsible for the upconversion in our system does not rely on multi-photon absorption via intermediate states, thus eliminating the need for high photon fluxes to achieve upconversion. The demonstrated upconversion paves the way for utilizing nanowires--with their inherent flexibility such as electrical contactability and the ability to position individual nanowires--for photon upconversion devices also at low photon fluxes, possibly down to the single photon level in optimised structures.
