| 1. |
- Laukkanen, P, et al.
(författare)
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Local variation in Bi crystal sites of epitaxial GaAsBi studied by photoelectron spectroscopy and first-principles calculations
- 2017
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 396, s. 688-694
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial Bi-containing III–V crystals (III-V1-xBix) have attracted increasing interest due to their potential in infrared applications. Atomic-scale characterization and engineering of bulk-like III-V1-xBix properties (e.g., Bi incorporation and defect formation) are challenging but relevant to develop applications. Toward that target, we report here that the traditional surface-science measurement of photoelectron spectroscopy (PES) is a potential, non-destructive method to be combined in the studies of bulk-like properties, when surface effects are properly removed. We have investigated epitaxial GaAs1-xBix films, capped by epitaxial AlAs layers, with high-resolution photoelectron spectroscopy. The Bi5d core-level spectra of GaAs1-xBix together with ab-initio calculations give direct evidence of variation of Bi bonding environment in the lattice sites. The result agrees with photoluminescence (PL) measurement which shows that the studied GaAs1-xBix films include local areas with higher Bi content, which contribute to PL but do not readily appear in x-ray diffraction (XRD). The measured and calculated Bi core-level shifts show also that Ga vacancies and Bi clusters are dominant defects.
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| 2. |
- Guina, M., et al.
(författare)
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Molecular Beam Epitaxy of Dilute Nitride Optoelectronic Devices
- 2018
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Ingår i: Molecular Beam Epitaxy: from Research to Mass Production. - 9780128121368 ; , s. 73-94
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Molecular beam epitaxy of dilute nitride materials has progressed a long way toward claiming its unique place as a technology that enables the development of new types of optoelectronics devices. This chapter starts by reviewing the particularities related to epitaxial incorporation of nitrogen into III–V materials using plasma-assisted molecular beam epitaxy. We then focus on describing the interplay between the growth parameters and nitrogen incorporation processes in dilute nitride arsenides (III-N-As). Emphasis is put on nitrogen-related growth kinetics that are accompanied by various bonding configurations and formation of several types of defects. Then we review the basics of MBE for dilute nitride antimonides (III-N-Sb) and dilute nitride phosphides (III-N-P). Finally, we review the growth optimization and properties of several classes of dilute nitride heterostructures for optoelectronics. These include uncooled long-wavelength laser diodes, ultrafast nonlinear devices, high power lasers enabling yellow-orange emission by frequency doubling, and high-efficiency multijunction solar cells, for which dilute nitride MBE technology is rapidly evolving and provides development opportunities.
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| 3. |
- Hakkarainen, Teemu, et al.
(författare)
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Te incorporation and activation as n-type dopant in self-catalyzed GaAs nanowires
- 2019
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Ingår i: Physical Review Materials. - 2475-9953. ; 3:8
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Tidskriftsartikel (refereegranskat)abstract
- Dopant atoms can be incorporated into nanowires either via the vapor-liquid-solid mechanism through the catalyst droplet or by the vapor-solid growth on the sidewalls. Si is a typical n-type dopant for GaAs, but in nanowires it often suffers from a strongly amphoteric nature in the vapor-liquid-solid process. This issue can be avoided by using Te, which is a promising but less common alternative for n-type doping of GaAs nanowires. Here, we present a detailed investigation of Te-doped self-catalyzed GaAs nanowires. We use several complementary experimental techniques, such as atom probe tomography, off-axis electron holography, micro-Raman spectroscopy, and single-nanowire transport characterization, to assess the Te concentration, the free-electron concentration, and the built-in potential in Te-doped GaAs nanowires. By combing the experimental results with a theoretical model, we show that Te atoms are mainly incorporated by the vapor-liquid-solid process through the Ga droplet, which leads to both axial and radial dopant gradients due to Te diffusion inside the nanowires and competition between axial elongation and radial growth of nanowires. Furthermore, by comparing the free-electron concentration from Raman spectroscopy and the Te-atom concentrations from atom probe tomography, we show that the activation of Te donor atoms is 100% at a doping level of 4×1018cm-3, which is a significant result in terms of future device applications.
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