| 1. |
- Chen, X, et al.
(författare)
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Shallow-terrace-like interface in dilute-bismuth GaSb/AlGaSb single quantum wells evidenced by photoluminescence
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:15, s. 153505-153507
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Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence (PL) measurements are performed on one GaSb/AlGaSb single-quantum-well (SQW) sample and two dilute-bismuth (Bi) GaSb/AlGaSb SQW samples grown at 360 and 380 °C, at low temperatures and under magnetic fields. Bimodal PL features are identified in the dilute-Bi samples, and to be accompanied by abnormal PL blueshift in the sample grown at 360 °C. The bimodal PL features are found to be from similar origins of band-to-band transition by magneto-PL evolution. Analysis indicates that the phenomenon can be well interpreted by the joint effect of interfacial large-lateral-scale islands and Al/Ga interdiffusion due to Bi incorporation. The interdiffusion introduces about 1-monolayer shrinkage to the effective quantum-well thickness, which is similar to the interfacial islands height, and the both together result in an unusual shallow-terrace-like interface between GaSbBi and AlGaSb. A phenomenological model is established, the Bi content of isoelectronic incorporation and the exciton reduced effective mass are estimated for the GaSbBi sample grown at 380 °C, and a value of about 21 meV/% is suggested for the bandgap bowing rate of GaSbBi. An effective routine is suggested for determining the Bi content and the depth of the shallow-terraces at interface in dilute-Bi SQW structures.
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| 2. |
- Fu, Yifeng, 1984, et al.
(författare)
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Templated Growth of Covalently Bonded Three-Dimensional Carbon Nanotube Networks Originated from Graphene
- 2012
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 24:12, s. 1576-1581
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Tidskriftsartikel (refereegranskat)abstract
- A template-assisted method that enables the growth of covalently bonded three-dimensional carbon nanotubes (CNTs) originating from graphene at a large scale is demonstrated. Atomic force microscopy-based mechanical tests show that the covalently bonded CNT structure can effectively distribute external loading throughout the network to improve the mechanical strength of the material.
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| 3. |
- Fülöp, Attila, 1988, et al.
(författare)
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Phase transition of bismuth telluride thin films grown by MBE
- 2014
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Ingår i: Applied Physics Express. - 1882-0786 .- 1882-0778. ; 7:4, s. Art. no. 045503-
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Tidskriftsartikel (refereegranskat)abstract
- A previously unreported phase transition between Bi2Te3 and Bi4Te3 in bismuth telluride grown by molecular beam epitaxy is recorded via XRD, AFM, and SIMS observations. This transition is found to be related to the Te/Bi beam equivalent pressure (BEP) ratio. BEP ratios below 17 favor the formation of Bi4Te3 while Bi2Te3 is formed at higher ratios. Transport measurements reveal that Bi2Te3 has higher electron mobility than Bi4Te3.
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| 4. |
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| 5. |
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| 6. |
- Gu, Yi, et al.
(författare)
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Optical properties of InGaAsBi/GaAs strained quantum wells studied by temperature-dependent photoluminescence
- 2013
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Ingår i: Chinese Physics B. - : IOP Publishing. - 1674-1056. ; 22:3, s. 037802-
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Tidskriftsartikel (refereegranskat)abstract
- The effect of bismuth on the optical properties of InGaAsBi/GaAs quantum well structures is investigated using the temperature-dependent photoluminescence from 12 K to 450 K. The incorporation of bismuth in the InGaAsBi quantum well is confirmed and found to result in a red shift of photoluminescence wavelength of 27.3 meV at 300 K. The photoluminescence intensity is significantly enhanced by about 50 times at 12 K with respect to that of the InGaAs quantum well due to the surfactant effect of bismuth. The temperature-dependent integrated photoluminescence intensities of the two samples reveal different behaviors related to various non-radiative recombination processes. The incorporation of bismuth also induces alloy non-uniformity in the quantum well, leading to an increased photoluminescence linewidth.
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| 7. |
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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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