| 1. |
- Hashemi, Seyed Ehsan, 1986, et al.
(författare)
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Effect of compositional interlayers on the vertical electrical conductivity of Si-doped AlN/GaN distributed Bragg reflectors grown on SiC''
- 2017
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Ingår i: Applied Physics Express. - 1882-0786 .- 1882-0778. ; 10:5, s. 055501-
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the effect of strain-compensating interlayers on the vertical electrical conductivity of Si-doped AlN/GaN distributed Bragg reflectors (DBRs). Samples with 10.5 mirror pairs were grown through plasma-assisted molecular beam epitaxy on SiC. Room-temperature current–voltage characteristics were measured vertically in mesas through 8 of the 10.5 pairs. The sample with no interlayers yields a mean specific series resistance of 0.044 Ω cm2 at low current densities, while three samples with 5/5-Å-thick, 2/2-nm-thick, and graded interlayers have resistivities between 0.16 and 0.34 Ω cm2. Thus, interlayers impair vertical current transport, and they must be designed carefully when developing conductive DBRs.
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| 2. |
- Huang, Dan, et al.
(författare)
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Ideal half-filled intermediate band position in CuGaS 2 generated by Sb-related defect complex: A first-principles study
- 2019
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Ingår i: Applied Physics Express. - : IOP Publishing. - 1882-0786 .- 1882-0778. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- Cu-based chalcopyrite compounds have attracted much attention for photovoltaic application, while some of them (like CuGaS 2 ) have energy gaps greater than the optimal value. An isolated and half-filled intermediate band located at the lower part of its original band gap exhibits in CuGaS 2 with (Sb Ga + Zn Ga ) or (Sb Ga + V Cu ) defect complex, in line with the intrinsic p-type conductivity of the host, revealed from our first-principles calculations. Subsequently, the absorption coefficients of CuGaS 2 can cover the full solar light spectrum efficiently. Based on the defect formation energy calculations, however, these defect complexes are hard to reach a large concentration under equilibrium condition. Nevertheless, non-equilibrium growth methods are suggested to prepare samples inheriting the excellent adsorption coefficients.
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| 3. |
- Wang, P., et al.
(författare)
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Heteroepitaxy growth of GaAsBi on Ge(100) substrate by gas source molecular beam epitaxy
- 2016
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Ingår i: Applied Physics Express. - : IOP Publishing. - 1882-0786 .- 1882-0778. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the growth of GaAsBi single-crystal film on Ge substrate by gas source molecular beam epitaxy. A high-quality GaAsBi epilayer has been obtained. It has been found that the surfactant effect of Bi suppresses the interdiffusion of Ge at the GaAsBi/Ge interface and reduces the misfit dislocation density. The Bi atoms occupy the As sites, as indicated by the appearance of GaBi-like TO(G) and LO(G) phonon modes in Raman spectra. In addition, the redshift of the GaAs-like LO(G) phonon frequency has been observed in the Raman spectra, owing to the Bi-induced biaxial strain and the alloying effect as well.
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| 4. |
- Yue, L., et al.
(författare)
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Novel InGaPBi single crystal grown by molecular beam epitaxy
- 2015
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Ingår i: Applied Physics Express. - : IOP Publishing. - 1882-0786 .- 1882-0778. ; 8:4, s. Art. no. 041201-
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Tidskriftsartikel (refereegranskat)abstract
- InGaPBi crystalline thin films with up to 2.1% bismuth concentration have been grown on GaAs substrates by molecular beam epitaxy. Rutherford backscattering spectrometry confirms that the majority of Bi atoms are located at substitutional lattice sites. The films exhibit good surface, structural, and interface quality, and their strains can be tuned from tensile to compressive by increasing the Bi content. InBi LO and GaBi LO vibrational modes in Raman spectroscopy were observed, and their intensities increased with Bi concentration. A weak photoluminescence signal was observed at 1.78 eV at room temperature for the sample with a Bi content of 0.5%.
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| 5. |
- Jayathilaka, Charith, et al.
(författare)
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Improved efficiency of electrodeposited p-CuO/n-Cu2O heterojunction solar cell
- 2015
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Ingår i: Applied Physics Express. - 1882-0778. ; 8:6
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Tidskriftsartikel (refereegranskat)abstract
- We report electrodeposition of n-type cuprous oxide (Cu2O) films on p-type CuO films electrodeposited on Ti substrates for forming p-CuO/n-Cu2O heterostructures. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis revealed that the films had good structural quality, with substrates being well-covered by the films. The p-CuO/n-Cu2O heterojunctions exhibited good photovoltaic properties and diode characteristics. The surfaces of Cu2O films subject to ammonium sulfide treatment exhibited enhanced photocurrents. Under AM 1.5 illumniation, the obtained sulfur-treated and annealed Ti/p-CuO/n-Cu2O/Au solar cell structure yielded energy conversion efficiency of 0.64%, with V-oc = 220mV and J(sc) = 6.8 mAcm(-2).
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| 6. |
- Le Febvrier, Arnaud, et al.
(författare)
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P-type Al-doped Cr-deficient CrN thin films for thermoelectrics
- 2018
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Ingår i: APPLIED PHYSICS EXPRESS. - : IOP PUBLISHING LTD. - 1882-0778. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- Thermoelectric properties of chromium nitride (CrN)-based films grown on c-plane sapphire by dc reactive magnetron sputtering were investigated. In this work, aluminum doping was introduced in CrN (degenerate n-type semiconductor) by co-deposition. Under the present deposition conditions, over-stoichiometry in nitrogen (CrN1+delta) rock-salt structure is obtained. A p-type conduction is observed with nitrogen-rich CrN combined with aluminum doping. The Cr0.96Al0.04N1.17 film exhibited a high Seebeck coefficient and a sufficient power factor at 300 degrees C. These results are a starting point for designing p-type/n-type thermoelectric materials based on chromium nitride films, which are cheap and routinely grown on the industrial scale. (C) 2018 The Japan Society of Applied Physics
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| 7. |
- Li, Borui, et al.
(författare)
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Acoustic surface transformation realized by acoustic-null materials using bilayer natural materials
- 2017
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Ingår i: APPLIED PHYSICS EXPRESS. - : IOP PUBLISHING LTD. - 1882-0778. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- We propose a general method, known as acoustic surface transformation (AST), to design novel acoustic devices and study the realization of such devices by using naturally available materials in broadband acoustic frequencies. All devices designed by AST only need one anisotropic homogeneous acoustic-null material (ANM). We design the ANM by exploiting natural material-based metal-fluid structures and verify that by numerical simulation. Unlike traditional methods, no complicated mathematical calculations are needed. We only need to design the geometrical shapes of the input and output surfaces of the devices. The proposed method will pave a new road for future acoustic design.
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| 8. |
- Li, Borui, et al.
(författare)
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Investigation of light trapping effect in hyperbolic metamaterial slow-light waveguides
- 2015
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Ingår i: APPLIED PHYSICS EXPRESS. - 1882-0778. ; 8:8
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Tidskriftsartikel (refereegranskat)abstract
- A hyperbolic metamaterial waveguide can reduce the group velocity of light down to zero by tuning a waveguide structure. The light trapping capability of a tapered hyperbolic metamaterial waveguide is comprehensively studied in this work. Although a pulse of light cannot be trapped forever in such a waveguide, the duration that light remains trapped can be flexibly prolonged by adjusting the volume filling ratio of the metamaterial or the material dispersion, in order to achieve a sufficiently long trapping time for practical applications.
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| 9. |
- Li, Borui, et al.
(författare)
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Reducing the dimensions of acoustic devices using anti-acoustic-null media
- 2018
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Ingår i: APPLIED PHYSICS EXPRESS. - : IOP PUBLISHING LTD. - 1882-0778. ; 11:2
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Tidskriftsartikel (refereegranskat)abstract
- An anti-acoustic-null medium (anti-ANM), a special homogeneous medium with anisotropic mass density, is designed by transformation acoustics (TA). Anti-ANM can greatly compress acoustic space along the direction of its main axis, where the size compression ratio is extremely large. This special feature can be utilized to reduce the geometric dimensions of classic acoustic devices. For example, the height of a parabolic acoustic reflector can be greatly reduced. We also design a brass-air structure on the basis of the effective medium theory to materialize the anti-ANM in a broadband frequency range. Numerical simulations verify the performance of the proposed anti-ANM.
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| 10. |
- Murakami, Hisashi, et al.
(författare)
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Homoepitaxial growth of beta-Ga2O3 layers by halide vapor phase epitaxy
- 2015
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Ingår i: Applied Physics Express. - : Japan Society of Applied Physics. - 1882-0778. ; 8:1, s. 015503-
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Tidskriftsartikel (refereegranskat)abstract
- Thick high-purity beta-Ga2O3 layers of high crystalline quality were grown homoepitaxially by halide vapor phase epitaxy (HVPE) using gaseous GaCl and O-2 on (001) beta-Ga2O3 substrates prepared by edge-defined film-fed growth. The surface morphology and structural quality of the grown layer improved with increasing growth temperature. X-ray diffraction omega-rocking curves for the (002) and (400) reflections for the layer grown at 1000 degrees C had small full widths at half maximum. Secondary ion mass spectrometry and electrical characteristics revealed that the growth of high-purity beta-Ga2O3 layers with low effective donor concentration (N-d - N-a less than 10(13) cm(-3)) is possible by HVPE. (C) 2015 The Japan Society of Applied Physics
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| 11. |
- UŽdavinys, Tomas Kristijonas, et al.
(författare)
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Impact of surface morphology on the properties of light emission in InGaN epilayers
- 2018
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Ingår i: Applied Physics Express. - : Japan Society of Applied Physics. - 1882-0778. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- Scanning near-field optical microscopy was used to study the influence of the surface morphology on the properties of light emission and alloy composition in InGaN epitaxial layers grown on GaN substrates. A strong correlation between the maps of the photoluminescence (PL) peak energy and the gradient of the surface morphology was observed. This correlation demonstrates that the In incorporation strongly depends on the geometry of the monolayer step edges that form during growth in the step-flow mode. The spatial distribution of nonradiative recombination centers-evaluated from PL intensity maps-was found to strongly anticorrelate with the local content of In atoms in the InGaN alloy.
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