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The Effect of Mg Doping on Optical and Structural Properties of GaN
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Mg is the most commonly used p-type dopant for GaN, however the impact of Mg incorporation on structural, morphological and optical properties of GaN is still not fully understood. Another research challenge is to understand and improve the properties of nonpolar GaN as it allows the fabrication of more efficient optoelectronic devices due to the absence of polarization fields.

Thus, the aim of this thesis was to explore the effect of Mg doping on polar c-plane GaN in Paper 1 and nonpolar m-plane GaN in Paper 2. The samples were grown by metal-organic vapor phase epitaxy with varying Mg content on free-standing GaN substrates. The studies were done by transmission electron microscopy (TEM) and low temperature cathodoluminescence (CL) with the aim to correlate the optical and structural data obtained by these techniques.

Polar c-plane GaN:Mg layers exhibit such structural defects as stackingfaults (SF) of a small size (5-10 nm). The basal plane SF (BSF)density was estimated to be ~ 105 − 106 cm−1 increasing with Mgconcentrations. Comparison between as-grown and annealed sampleshas not shown significant difference in structural or optical properties.Characteristic broad emission lines observed in CL in the rangeof 3.29 − 3.41 eV have been attributed to SF-related emissions byanalogy with nonpolar undoped GaN films grown heteroepitaxially.Acceptor bound exciton (ABE) emission and SF-related peaks havedemonstrated metastability. CL mapping performed on the TEMsamples at the energies corresponding to SF-related peaks has confirmedthat the origin of these lines is associated with Mg-doped GaNlayers. In nonpolar m-plane GaN:Mg layers similar BSFs have been observed. In addition more extended BSFs and prismatic SFs wereidentified at the interface with the GaN substrate. For the m-planesamples with Mg concentration of ~ 1019 cm−3 a number of fine CLlines have been detected in the region of 3.3-3.4 eV. Their shape andappearance were unlike the SF-related emissions in the case of c-planeGaN discussed in Paper 1. These peaks are not likely to be associatedwith donor-acceptor pair (DAP) recombination as has been proved byestimation of the separated DAP energies and by CL mapping experiment.A tentative explanation is given to these peaks as being relatedto excitons bound to some low symmetry acceptor defect centers.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 33 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1520
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-75428ISBN: 9789175199504 (print)OAI: oai:DiVA.org:liu-75428DiVA: diva2:506677
Supervisors
Available from: 2012-02-29 Created: 2012-02-29 Last updated: 2017-12-15Bibliographically approved
List of papers
1. Luminescence related to high density of Mg-induced stacking faults in homoepitaxially grown GaN
Open this publication in new window or tab >>Luminescence related to high density of Mg-induced stacking faults in homoepitaxially grown GaN
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2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 7, 075324- p.Article in journal (Refereed) Published
Abstract [en]

The effect of Mg doping on stacking fault (SF) formation in c-plane GaN grown by metal-organic chemical-vapor deposition has been studied for Mg concentration between 2 x 10(18) cm(-3) and 5 x 10(19) cm(-3). Transmission electron microscopy studies demonstrate a direct correlation between the increasing Mg content and the number of small (3-10-nm long) SFs present. The energy dispersive x-ray analysis (EDX) line profile of a SF shows that the Mg-impurity atom resides at a distance approximately 5 nm from the SF. Cathodoluminescence (CL) mapping reveals that the Mg-doped regions radiate at energies corresponding to known SF emission peaks. SF-related peaks in CL spectra show metastability, which may be attributed to transfer processes involving Mg acceptors and nearby associated SFs.

Place, publisher, year, edition, pages
American Physical Society, 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-70330 (URN)10.1103/PhysRevB.84.075324 (DOI)000293830600018 ()
Note
Funding Agencies|Swedish Energy Agency||Swedish Research Council (VR)||Swedish Governmental Agency for Innovation Systems (VINNOVA)||Available from: 2011-09-02 Created: 2011-09-02 Last updated: 2017-12-08
2. Optical and structural studies of homoepitaxially grown m-plane GaN
Open this publication in new window or tab >>Optical and structural studies of homoepitaxially grown m-plane GaN
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2012 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 17, 172108- p.Article in journal (Refereed) Published
Abstract [en]

We report on cathodoluminescence (CL) and transmission electron microscopy (TEM) studies of m-plane Mg-doped GaN layers grown by metal-organic vapor phase epitaxy (MOVPE). The layers contain basal plane and prismatic stacking faults (SFs) with a density of ~106 cm-1. Broad emission peaks commonly ascribed to SF were found to be insignificant in these samples. However, a set of quite strong and sharp lines were detected in the same spectral region 3.36-3.42 eV. The observed peaks are tentatively explained as excitons bound to some point defects by analogy with p-type GaAs, since donor-acceptor pair (DAP) recombination was ruled out by the CL mapping experiments.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2012
Keyword
GaN, m-plane, Mg-doping, stacking faults, cathodoluminescence
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-75427 (URN)10.1063/1.4706258 (DOI)000303340300039 ()
Note
funding agencies|Swedish Energy Agency||Swedish Research Council (VR) Linnaeus Environment LiLi-NFM at Linkoping||Carl Trygger Foundation||Swedish Governmental Agency for Innovation Systems (VINNOVA)||National Science Foundation, Division of Materials Research||Available from: 2012-02-29 Created: 2012-02-29 Last updated: 2017-12-07Bibliographically approved

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