| 1. |
- Wernersson, Lars-Erik, et al.
(author)
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Epitaxially overgrown, stable W-GaAs Schottky contacts with sizes down to 50 nm
- 2002
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In: Journal of Vacuum Science and Technology B. - : American Vacuum Society. - 1520-8567. ; 20:2, s. 580-589
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Journal article (peer-reviewed)abstract
- A processing scheme for the fabrication of embedded W-GaAs contacts has been established and the resulting contact characteristics have been evaluated. The main advantage of these contacts is that they are stable during high-temperature epitaxial overgrowth. The fabrication scheme is based on a liftoff process with electron beam evaporation of tungsten and subsequent epitaxial overgrowth using metalorganic vapor phase epitaxy. Various methods were used to characterize the buried contacts. First, the structural properties of GaAs surrounding embedded W features, with widths down to 50 nm, were characterized by high-resolution transmission electron microscopy. Measurements of the conductivity in individual, buried wires were performed in order to study the influence of the overgrowth process on the properties of the tungsten. We also evaluated the current-voltage characteristics for macroscopic contacts, which revealed a clear dependence on processing parameters. Optimized processing conditions could thus be established under which limited contact degradation occurred during overgrowth. Finally, we used the overgrowth technique to perform a detailed investigation of the electrical and optical properties of floating-potential embedded nano-Schottky contacts by space-charge spectroscopy.
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| 2. |
- Wernersson, Lars-Erik, et al.
(author)
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Metalorganic vapor phase epitaxy-grown GaP/GaAs/GaP and GaAsP/GaAs/GaAsP n-type resonant tunnelling diodes
- 2002
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:10, s. 1841-1843
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Journal article (peer-reviewed)abstract
- We have studied GaP/GaAs/GaP and GaAsxP1-x/GaAs/GaAsxP1-x double-barrier resonant tunnelling diodes grown by metalorganic vapor phase epitaxy. We find that GaP tensile strained barriers in GaP/GaAs/GaP diodes may be grown with a barrier thickness below the critical thickness of about 12 monolayers. However, a corrugation of the strained barrier is observed by transmission electron microscopy. This variation may explain the low peak-to-valley ratio of the diodes (about 2). In contrast, GaAsxP1-x/GaAs/GaAsxP1-x resonant tunnelling diodes have been grown with a homogeneous thickness of the barriers, consequently showing a substantially improved electrical performance compared to the GaP diodes with peak-to-valley ratios >5.
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| 3. |
- Wernersson, Lars-Erik, et al.
(author)
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Thin layers of GaInP, GaP and GaAsP in metalorganic vapour phase epitaxy-grown resonant tunnelling diodes
- 2002
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In: Applied Surface Science. - 1873-5584. ; 190:1, s. 252-257
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Journal article (peer-reviewed)abstract
- We have studied the epitaxial growth and electrical performance of Al-free, GaAs-based, resonant tunnelling diodes (RTDs) including thin barriers of GaInP, GO, or GaAsxP1-x. n-Type tunnelling diodes have been fabricated and the symmetry in the current-voltage (I-V) characteristics, as well as the peak-to-valley ratios, are found to be sensitive probes for the inter-face quality in the heterostructures. For GaInP RTDs, we show that the introduction of Gap intermediate layers is crucial for the realisation. of a useful tunnelling current. RTDs including thin barriers (less than about 10 monolayers (ML)) of Gap are realised, but the strong mismatch between the materials limit the useful thickness. Finally, RTDs with GaAslambdaP1-x alloys are fabricated showing the best peak-to-valley ratio of the diodes (about 5), as well as a symmetric I-V characteristics. The electrical data are further compared to studies by transmission electron microscopy (TEM) in the various material systems.
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| 4. |
- Berg, Alexander, et al.
(author)
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Growth and characterization of wurtzite GaP nanowires with control over axial and radial growth by use of HCl in-situ etching
- 2014
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 386, s. 47-51
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Journal article (peer-reviewed)abstract
- We report on the synthesis of non-tapered wurtzite (WZ) GaP nanowires by use of in-situ etching and the structural and optical characterization thereof. HCl was evaluated as an in-situ etchant in order to impede the onset of radial growth since the WZ crystal phase in GaP nanowires preferentially grows at relatively high growth temperatures around 600 degrees C, at which strong radial growth typically occurs. Transmission electron microscopy measurements confirmed non-tapered WZ GaP nanowires after growth. Photoluminescence characterization revealed defect related red emission, possibly related to transitions within the bandgap. Raman measurements show that the phonon energies in WZ GaP are very close in energy to the phonon energies in zinc blende GaP. (C) 2013 Elsevier B.V. All rights reserved.
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| 5. |
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| 6. |
- Bi, Zhaoxia, et al.
(author)
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Bottom-up approaches to microLEDs emitting red, green and blue light based on GaN nanowires and relaxed InGaN platelets
- 2023
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In: Chinese Physics B. - : IOP Publishing. - 1674-1056. ; 32
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Journal article (peer-reviewed)abstract
- 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.
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| 7. |
- Bi, Zhaoxia, et al.
(author)
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High In-content InGaN nano-pyramids : Tuning crystal homogeneity by optimized nucleation of GaN seeds
- 2018
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 123:2
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Journal article (peer-reviewed)abstract
- Uniform arrays of submicron hexagonal InGaN pyramids with high morphological and material homogeneity, reaching an indium composition of 20%, are presented in this work. The pyramids were grown by selective area metal-organic vapor phase epitaxy and nucleated from small openings in a SiN mask. The growth selectivity was accurately controlled with diffusion lengths of the gallium and indium species, more than 1 μm on the SiN surface. High material homogeneity of the pyramids was achieved by inserting a precisely formed GaN pyramidal seed prior to InGaN growth, leading to the growth of well-shaped InGaN pyramids delimited by six equivalent 10 1 ̄ 1 facets. Further analysis reveals a variation in the indium composition to be mediated by competing InGaN growth on two types of crystal planes, 10 1 ̄ 1 and (0001). Typically, the InGaN growth on 10 1 ̄ 1 planes is much slower than on the (0001) plane. The formation of the (0001) plane and the growth of InGaN on it were found to be dependent on the morphology of the GaN seeds. We propose growth of InGaN pyramids seeded by 10 1 ̄ 1-faceted GaN pyramids as a mean to avoid InGaN material grown on the otherwise formed (0001) plane, leading to a significant reduction of variations in the indium composition in the InGaN pyramids. The InGaN pyramids in this work can be used as a high-quality template for optoelectronic devices having indium-rich active layers, with a potential of reaching green, yellow, and red emissions for LEDs.
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| 8. |
- Bi, Zhaoxia, et al.
(author)
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InGaN Platelets : Synthesis and Applications toward Green and Red Light-Emitting Diodes
- 2019
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In: Nano Letters. - : American Chemical Society. - 1530-6984 .- 1530-6992. ; 19:5, s. 2832-2839
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Journal article (peer-reviewed)abstract
- In this work, we present a method to synthesize arrays of hexagonal InGaN submicrometer platelets with a top c-plane area having an extension of a few hundred nanometers by selective area metal-organic vapor-phase epitaxy. The InGaN platelets were made by in situ annealing of InGaN pyramids, whereby InGaN from the pyramid apex was thermally etched away, leaving a c-plane surface, while the inclined {101Ì1} planes of the pyramids were intact. The as-formed c-planes, which are rough with islands of a few tens of nanometers, can be flattened with InGaN regrowth, showing single bilayer steps and high-quality optical properties (full width at half-maximum of photoluminescence at room temperature: 107 meV for In 0.09 Ga 0.91 N and 151 meV for In 0.18 Ga 0.82 N). Such platelets offer surfaces having relaxed lattice constants, thus enabling shifting the quantum well emission from blue (as when grown on GaN) to green and red. For single InGaN quantum wells grown on the c-plane of such InGaN platelets, a sharp interface between the quantum well and the barriers was observed. The emission energy from the quantum well, grown under the same conditions, was shifted from 2.17 eV on In 0.09 Ga 0.91 N platelets to 1.95 eV on In 0.18 Ga 0.82 N platelets as a result of a thicker quantum well and a reduced indium pulling effect on In 0.18 Ga 0.82 N platelets. On the basis of this method, prototype light-emitting diodes were demonstrated with green emission on In 0.09 Ga 0.91 N platelets and red emission on In 0.18 Ga 0.82 N platelets.
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| 9. |
- Bi, Zhaoxia, et al.
(author)
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InN quantum dots on GaN nanowires grown by MOVPE
- 2014
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In: physica status solidi (c). - : Wiley. - 1862-6351 .- 1610-1642 .- 1610-1634. ; 11, s. 421-424
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Journal article (peer-reviewed)abstract
- In this work, growth of InN quantum dots (QDs) on GaN nanowires (NWs) by metal-organic vapour phase epitaxy is demonstrated, illustrating the feasibility to combine 0D and 1D structures for nitride semiconductors. Selective area growth was used to generate arrays of c-oriented GaN NWs using Si3N4 as the mask material. In general, InN QDs tend to form at the NW edges between the m-plane side facets, but the QD growth can also be tuned to the side facets by controlling the growth temperature and the growth rate. TEM characterization reveals that I1-type stacking faults are formed in the QDs and originate from the misfit dislocations at the InN/GaN interface. Photoluminescence measurement at 4 K shows that the peak shifts to high energy with reduced dot size. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 10. |
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