| 11. |
- Han, Y., et al.
(författare)
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Critical Thickness and Radius for Axial Heterostructure Nanowires Using Finite Element Method
- 2009
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 9:5, s. 1921-1925
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Tidskriftsartikel (refereegranskat)abstract
- Finite-element methods are used to simulate a heterostructured nanowire grown on a compliant mesa substrate. The critical thickness is calculated based on the overall energy balance approach. The strain field created by the first pair of misfit dislocations, which offsets the initial coherent strain field, is simulated. The local residual strain is used to calculate the total residual strain energy. The three-dimensional model shows that there exists a radius-dependent critical thickness below which no misfit dislocations could be generated. Moreover, this critical thickness becomes infinity for a radius less than some critical values. The simulated results are in good agreement with the experimental data. The critical radius from this work is smaller than that obtained from previous models that omit the interaction between the initial coherent strain field and the dislocation-induced strain field.
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| 12. |
- Pan, W. W., et al.
(författare)
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Raman scattering studies of dilute InP1-xBix alloys reveal unusually strong oscillator strength for Bi-induced modes
- 2015
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 30:9
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Tidskriftsartikel (refereegranskat)abstract
- Room-temperature Raman scattering studies of new InP1-xBix alloys grown by molecular beam epitaxy are reported. Two new Bi-induced vibrations observed at 149 and 171 cm-1 are assigned to InBi-like TO and LO phonon modes, respectively, and exhibit an unusually strong intensity for the dilute regime. Two additional modes at 311 and 337 cm-1 are resolved as well with unknown origins. The Raman intensities of the InBi-like TO and LO bands, as well as the new mode at 337 cm-1, exhibit strong and linear dependence on the Bi concentration for the composition range studied, 0.003 ≤ x ≤ 0.023. This correlation may serve as a fast and convenient means of characterizing bismuth composition not only in the ternary alloy InP1-xBix but also in the quaternaries such as In1-yGayP1-xBix and In1-yAlyP1-xBix.
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| 13. |
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| 14. |
- Segercrantz, N., et al.
(författare)
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Defect studies in MBE grown GaSb1-x Bi x layers
- 2014
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Ingår i: AIP Conference Proceedings. - : AIP Publishing LLC. - 1551-7616 .- 0094-243X. ; 1583, s. 174-177
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Konferensbidrag (refereegranskat)abstract
- Positron annihilation spectroscopy in Doppler broadening mode is used to study epitaxial layers of GaSb 1-x Bi x on undoped GaSb. The samples were grown by Molecular Beam Epitaxy at different temperatures and with different Bi/Sb beam equivalent pressure ratios resulting in Bi concentrations of 0-0.7 %. The results show a relationship between the growth parameters and Doppler broadening parameters. Incorporating Bi into GaSb decreases the vacancy concentration in the epitaxial layers compared to the sample with no Bi in the epitaxial layer.
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| 15. |
- Segercrantz, N, et al.
(författare)
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Defect studies in MBE grown GaSbBi layers
- 2013
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Ingår i: 27th International Conference on Defects in Semiconductors 2013, Bologna, Italy, 2013.
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Konferensbidrag (refereegranskat)
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| 16. |
- Segercrantz, Natalie, et al.
(författare)
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Defect studies in MBE grown GaSbBi layers
- 2013
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Ingår i: The 17th European Molecular Beam Epitaxy Workshop (EuroMBE), March 10th-13th, 2013, Levi, Finland.
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Konferensbidrag (refereegranskat)abstract
- Gallium antimonide is an interesting material both from a material and a device point of view. Thedirect, narrow band gap and high electron mobility makes the compound semiconductor a suitablecandidate for high speed electronics and optoelectric devices. It can also be used as a substratematerial for other ternary or quaternary III–V compounds whose band gaps cover a wide spectralrange from 0.8 to 4.3 ?m. [1]Incorporating Bi into GaSb has shown to have several advantages compared to, for example, GaNSb.Not only is the band gap reduced [2], but the width of the gap depends very weakly on temperature [3]and the electron mobility is higher than that of GaNSb [4]. The spin-orbit splitting is also larger thanthe actual band gap which could be used for suppressing Auger-recombinations [5].Using positron annihilation spectroscopy (PAS) in Doppler broadening mode, we have studiedsamples of GaSbBi epitaxial layers on GaSb substrates. The PAS technique is based on the interactionbetween positrons and electrons in solids and can be used for e.g. vacancy defect characterization inthin layers. The studied samples were MBE-grown and the main varied growth parameter wastemperature, which lead to different Bi concentrations. The Bi concentrations were 0 - 0.7 %, theepitaxial layer thickness was 200 nm. The substrate was Te-doped (n-type) GaSb.From the measured results, differences between the samples grown under different conditions can beclearly observed. A short diffusion length for the positrons is observed in all of the epitaxial layers,which indicates an increase in positron trapping defects in the layers, compared to the substrate.Furthermore, the Doppler broadening annihilation parameters in the epitaxial layers also seem todepend on the growth temperature and hence, also on the Bi concentration. In order to be able todistinguish the influence of the Bi concentration from the influence of vacancy defects on the Dopplerbroadening parameters, more accurate measurements need to be conducted. We hope to achieve abetter understanding of the positron trapping defect in the epitaxial layers by using coincidenceDoppler broadening.
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| 17. |
- Segercrantz, N., et al.
(författare)
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Point defect balance in epitaxial GaSb
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:8, s. art. no. 082113-
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Tidskriftsartikel (refereegranskat)abstract
- Positron annihilation spectroscopy in both conventional and coincidence Doppler broadening mode is used for studying the effect of growth conditions on the point defect balance in GaSb:Bi epitaxial layers grown by molecular beam epitaxy. Positron annihilation characteristics in GaSb are also calculated using density functional theory and compared to experimental results. We conclude that while the main positron trapping defect in bulk samples is the Ga antisite, the Ga vacancy is the most prominent trap in the samples grown by molecular beam epitaxy. The results suggest that the p–type conductivity is caused by different defects in GaSb grown with different methods.
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| 18. |
- Shao, Jun, et al.
(författare)
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Photoluminescence probing of interface evolution with annealing in InGa(N)As/GaAs single quantum wells
- 2015
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 118:16, s. 165305-
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Tidskriftsartikel (refereegranskat)abstract
- The effects of thermal annealing on the interfaces of InGa(N)As/GaAs single quantum wells(SQWs) are investigated by excitation-, temperature-, and magnetic field-dependent photoluminescence(PL). The annealing at 750 °C results in more significant blueshift and narrowing to the PLpeak than that at 600 °C. Each of the PL spectra can be reproduced with two PL components: (i)the low-energy component (LE) keeps energetically unchanged, while the high-energy component(HE) moves up with excitation and shows at higher energy for the In0.375Ga0.625As/GaAs butcrosses over with the LE at a medium excitation power for the In0.375Ga0.625N0.012As0.988/GaAsSQWs. The HE is broader than the corresponding LE, the annealing at 750 °C narrows the LE andHE and shrinks their energetic separation; (ii) the PL components are excitonic, and the InGaNAsshows slightly enhanced excitonic effects relative to the InGaAs SQW; (iii) no typical S-shape evolutionof PL energy with temperature is detectable, and similar blueshift and narrowing are identifiedfor the same annealing. The phenomena are mainly from the interfacial processes. Annealingimproves the intralayer quality, enhances the interfacial In-Ga interdiffusion, and reduces the interfacialfluctuation. The interfacial interdiffusion does not change obviously by the small N contentand hence similar PL-component narrowing and blueshift are observed for the SQWs after a nominallyidentical annealing. Comparison with previous studies is made and the PL measurementsunder different conditions are shown to be effective for probing the interfacial evolution in QWs.
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| 19. |
- Song, Yuxin, 1981, et al.
(författare)
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Dilute Bismides for Mid-IR Applications
- 2013
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Ingår i: Springer Series in Materials Science. - New York, NY : Springer New York. - 2196-2812 .- 0933-033X. - 9781461481218 ; , s. 1-27
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Dilute bismides are a group of emerging materials with unique properties. Incorporation of a small amount of Bi in common III–V host materials results in large band-gap reduction and strong spin-orbit splitting, leading to potential applications in mid-infrared (Mid-IR) optoelectronics. In this chapter, we review recent progresses on epitaxy and characterizations of novel bismides, i.e., GaSb1−x Bi x , InSb1 − x Bi x , InAs1 − x Bi x , and InAsSbBi. Although these dilute bismides have been successfully grown, to obtain high Bi incorporations and retain high crystal quality is still very challenging.
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| 20. |
- Song, Yuxin, 1981, et al.
(författare)
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Dilute bismides for near and mid-infrared applications
- 2013
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Ingår i: 2013 15th International Conference on Transparent Optical Networks (ICTON). - 2162-7339. - 9781479906826 ; , s. 6602735-
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Konferensbidrag (refereegranskat)abstract
- Dilute bismides are a group of emerging materials with unique properties. Incorporation of a small amount of Bi in common III-V host materials results in large band-gap reduction and strong spin-orbit splitting, leading to potential applications in near-infrared (NIR) and mid-infrared (MIR) optoelectronics. Recent progresses on molecular beam epitaxy (MBE) of novel III-Sb-Bi, i.e. GaSbBi and InSbBi thin films from our group are summarised in this paper. Quantum well structures based on GaSbBi and InGaAsBi aiming for the optical communication window were grown and characterized.
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