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Electron spin filtering by thin GaNAs/GaAs multiquantum wells
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-7155-7103
Université de Toulouse, LPCNO: INSA, UPS, CNRS, 135 avenue de Rangueil, 31077 Toulouse Cedex, France.
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2010 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 5, 052104- p.Article in journal (Refereed) Published
Abstract [en]

Effectiveness of the recently discovered defect-engineered spin-filtering effect is closely examined in GaNAs/GaAs multiquantum wells (QWs) as a function of QW width. In spite of narrow well widths of 3-9 nm, rather efficient spin filtering is achieved at room temperature. It leads to electron spin polarization larger than 18% and an increase in photoluminescence intensity by 65% in the 9 nm wide QWs. A weaker spin filtering effect is observed in the narrower QWs, mainly due to a reduced sheet concentration of spin-filtering defects (e.g., Ga-i interstitial defects).

Place, publisher, year, edition, pages
2010. Vol. 96, no 5, 052104- p.
Keyword [en]
electron spin polarisation, gallium arsenide, III-V semiconductors, nitrogen compounds, photoluminescence, semiconductor quantum wells
National Category
Engineering and Technology Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-54084DOI: 10.1063/1.3299015ISI: 000274319500045OAI: oai:DiVA.org:liu-54084DiVA: diva2:298245
Available from: 2010-02-22 Created: 2010-02-22 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Spin-dependent recombination in Ga(In)NAs alloys
Open this publication in new window or tab >>Spin-dependent recombination in Ga(In)NAs alloys
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The abilities to control and manipulate electron spin, especially in semiconductors, lead to many interesting proposals for spin-functional devices in future spintronics and quantum information technology. A key requirement for the success of these proposals is that the spin functionality should be operational at room temperature (RT), which remains as a great challenge. Very recently, spin-dependent recombination (SDR) via paramagnetic defects that dominate in carrier recombination, i.e Gai - interstitial defects in Ga(In)NAs alloys, has been shown to turn the material into a highly efficient defectengineered spin filter operating at RT and without requiring an external applied field. This finding has demonstrated the great potential of such a spin filter as an efficient spin source, which is capable of generating up to 90% electron spin polarization at RT.

Essential to realization of this attractive application in spintronics is a fundamental understanding of this alloy system and their related spin filtering defects. Therefore, factors controlling this spin filter must be studied, understood and optimized. In this licentiate thesis, we aim at optimization of the spin filtering effect in Ga(In)NAs alloys and the related quantum structures by studying influence of material fabrication techniques, post growth treatments and material structures. In paper I, we employed the optically detected magnetic resonance (ODMR) technique to study formation of Ga interstitial-related defects in Ga(In)NAs alloys. We showed that these spin-filtering defects are common grown-in defects in these alloys, independent of the employed fabrication techniques and post-growth annealing treatment. The defect formation was suggested to be thermodynamically favorable in the presence of nitrogen, possibly because of local strain compensation. In paper II, we further investigated the role of post-growth hydrogen treatment in the spin filtering effect in GaNAs epilayers and GaNAs/GaAs multiple quantum wells (QWs). From optical orientation studies, we found that the hydrogen treatment has led to nearly complete quenching of the spin filtering effect. Together with a detailed ODMR study and a rate equation analysis, the observed effect of hydrogen was attributed to hydrogen passivation of the spin filtering defects, likely by formation of complexes between the Gai-interstitial defects and hydrogen. This finding also ruled out the possibility of hydrogen as a part of the spin filtering defects in the as-grown materials, though hydrogen is known to be commonly present during the growth process.

In Paper III, we examined the effectiveness of the spin filtering effect in the GaNAs/GaAs QWs as a function of QW width. Even with rather narrow QW widths of 3-9 nm, the spin filtering effect was shown to be efficient. It was further revealed that the spin filtering effect is more efficient in the wider QWs. From studies of transient behavior of photoluminescence and ODMR, it was concluded that this was mainly due to an increase in the sheet concentration of the spin filtering defects.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 34 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1533
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-77153 (URN)LIU-TEK-LIC-2012:18 (Local ID)978-91-7519-875-0 (ISBN)LIU-TEK-LIC-2012:18 (Archive number)LIU-TEK-LIC-2012:18 (OAI)
Presentation
2012-05-30, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2012-05-07 Created: 2012-05-07 Last updated: 2017-03-27Bibliographically approved
2. Room-temperature defect-engineered spin functionalities in Ga(In)NAs alloys
Open this publication in new window or tab >>Room-temperature defect-engineered spin functionalities in Ga(In)NAs alloys
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Semiconductor spintronics is one of the most interesting research fields that exploits both charge and spin properties for future photonics and electronic devices. Among many challenges of using spin in semiconductors, efficient generation of electron spin polarization at room temperature (RT) remains difficult. Recently, a new approach using defect-mediated spin filtering effect, employing -interstitial defects in Ga(In)NAs alloys, has been shown to turn the material into an efficient spin-polarized source capable of generating >40% conduction electron spin polarization at RT without an application of external fields. In order to fully explore the defectengineered spin functionalities, a better understanding and control of the spin filtering effects is required. This thesis work thus aims to advance our understanding, in terms of both physical and material insights, of the recently discovered spin filtering defects in Ga(In)NAs alloys. We have focused on the important issues of optimization and applications of the spin filtering effects.

To improve spin filtering efficiency, important material and defect parameters must be addressed. Therefore, in Papers I–III formation of the  defects in Ga(In)NAs alloys has been examined under different growth and post-growth treatment conditions, as well as in different structures. We found that the  defects were the dominant and important nonradiative recombination centers in Ga(In)NAs epilayers and GaNAs/GaAs multiple quantum wells, independent of growth conditions and post-growth annealing. However, by varying growth and post-growth conditions, up to four configurations of the  defects, exhibiting different hyperfine  interaction (HFI) strengths between defect electron and nuclear (e-n) spins, have been found. This difference was attributed to different interstitial sites and/or complexes of  . Further studiesfocused on the effect of post-growth hydrogen (H) irradiation on the spin filtering effect. Beside the roles of H passivation of N resulting in bandgap reopening of the alloys, H treatment was shown to lead to complete quenching of the spin filtering effect, accompanied by strong suppression in the concentrations of the  defects. We concluded that the observed effect was due to the passivation of the  defects by H, most probably due to the formation of H- complexes.

Optimizing spin filtering efficiency also requires detailed knowledge of spin interactions at the defect centers. This issue was addressed in Papers IV and V. From both experimental and theoretical studies, we were able to conclude that the HFI between e-n spins at the  defects led to e-n spin mixing, which degraded spin filtering efficiency at zero field.  Moreover, we have identified the microscopic origin of electron spin relaxation (T1) at the defect centers, that is, hyperfine-induced e-n spin cross-relaxation. Our finding thus provided a guideline to improve spin filtering efficiency by selectively incorporating the  defects with weak HFI by optimizing growth and post-growth treatment conditions, or by searching for new spin filtering defect centers containing zero nuclear spin.

The implementation of the defect-engineered spin filtering effect has been addressed in Papers VI–VIII. First, we experimentally demonstrated for the first time at RT an efficient electron spin amplifier employing the  defects in Ga(In)NAs alloys, capable of amplifying a weak spin signal up to 27 times with a high cut-off frequency of 1 GHz. We further showed that the defectmediated spin amplification effect could turn the GaNAs alloy into an efficient RT optical spin detector. This enabled us to reliably conduct in-depth spin injection studies across a semiconductor heterointerface at RT. We found a strong reduction of electron spin polarization after optical spin injection from a GaAs layer into an adjacent GaNAs layer. This observation was attributed to severe spin loss across the heterointerface due to structural inversion asymmetry and probably also interfacial point defects.

Finally, we went beyond the generation of strongly polarized electron spins. In Paper IX we focused on an interesting aspect of using strongly polarized electron spins to induce strong nuclear spin polarization at RT, relevant to solid-state quantum computation using a defect nuclear spin of long spin memory as a quantum bit (qubit). By combining the spin filtering effect and the HFI, we obtained a sizeable nuclear spin polarization of ~15% at RT that could be sensed by conduction electrons. This demonstrated the feasibility of controlling defect nuclear spins via conduction electrons even at RT, the first case ever being demonstrated in a semiconductor.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 49 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1607
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-107621 (URN)10.3384/diss.diva-107621 (DOI)978-91-7519-293-2 (ISBN)
Public defence
2014-08-22, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-06-17 Created: 2014-06-17 Last updated: 2017-03-27Bibliographically approved

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Puttisong, YuttapoomWang, XingjunBuyanova, IrinaChen, Weimin

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