Dislocation luminescence in GaN single crystals under nanoindentation
© Huang et al.; licensee Springer. 2014
Received: 24 August 2014
Accepted: 4 November 2014
Published: 1 December 2014
This work presents an experimental study on the dislocation luminescence in GaN by nanoindentation, cathodoluminescence, and Raman. The dislocation luminescence peaking at 3.12 eV exhibits a series of special properties in the cathodoluminescence measurements, and it completely disappears after annealing at 500°C. Raman spectroscopy shows evidence for existence of vacancies in the indented region. A comprehensive investigation encompassing cathodoluminescence, Raman, and annealing experiments allow the assignment of dislocation luminescence to conduction-band-acceptor transition involving Ga vacancies. The nanoscale plasticity of GaN can be better understood by considering the dislocation luminescence mechanism.
GaN-related III-nitride materials have gained an unprecedented attention due to their wide-ranging applications such as short-wavelength optoelectronic devices , high-electron-mobility transistor , and semiconductor lasers . However, due to the lack of large-sized bulk materials, the majority of GaN-related alloys or structures are grown heteroepitaxially on foreign substrates such as sapphire or SiC. Consequently, those alloys or structures usually contain a high density of dislocations which can have detrimental effects on the performance of devices. In spite of the considerable progress made in the last decade in GaN, an in-depth understanding of the properties of dislocation is needed due to their paramount importance in the growth of most conventional semiconductor materials and in the manufacture of semiconductor devices. However, the optical and electronic properties of as-grown dislocations may be greatly affected by the unintentionally introduced impurities and defects during the growth process. Thus, it is interesting to clarify intrinsic optical properties of dislocations both in basic research and technological applications.
Nanoindentation is an ideal technique for studying the fundamental behaviors and properties of dislocations in a crystal by introducing dislocations into a small volume that is initially defect-free. Consequently, nanoindentation experiments and simulations can be used to demonstrate mechanisms governing dislocation nucleation in a broad range of fields and applications [4, 5]. Especially, there has also been a considerable effort to determine the properties of plastic deformation in GaN epilayers and GaN bulk crystals using indentation techniques [6–14]. Local strain fields of the indentation have been studied by a micro-Raman spectroscopy [11, 13], and the formation of contact-induced dislocations has been investigated via cathodoluminescence (CL) spectroscopy [6–9, 11] and transmission electron microscopy (TEM) [6–8, 10, 12]. However, most of these earlier studies mainly focused on the microstructure of the indentation-induced dislocations in GaN; the fundamental dislocation luminescence mechanism of GaN is not understood fully. This work presents a comprehensive study encompassing nanoindentation, CL, and Raman techniques aimed at revealing the origin of the dislocation luminescence in GaN.
A 1.5-mm-thick freestanding GaN layer with an area size of about 20 mm × 20 mm was selected for the indentation tests. The thick GaN layer grown by hydride vapor phase epitaxy on the c-plane of sapphire substrate was self-separated during cooling down from the growth temperature. The dislocation density of the GaN freestanding layer was about 5 × 105 cm−2 as estimated by the etch pit density. The background carrier concentration was about 1 × 1016 cm−3 from the analysis of the Hall data.
Nanoindentation tests were performed on the GaN (0001) surface using a nanoindentation system (Nano Indenter G200, Agilent Technologies, Inc., Santa Clara, CA, USA). A Berkovich indenter tip with a radius of curvature of 50 nm was employed for indentation experiments. The strain rate was set at 0.05 s−1 during nanoindentation tests. Scanning electron microscopy (Quanta 400 FEG, FEI, Hillsboro, OR, USA) - cathodoluminescence (MonoCL3+, Gatan, Inc., Pleasanton, CA, USA) system was used to characterize the indentation. The Raman spectra measured by a LabRAM HR 800 spectrometer (LabRAM HR 800 spectrometer, HORIBA Scientific, Edison, NJ, USA) were excited with the 633.28-nm He-Ne laser allowing for a lateral resolution of better than 1 μm.
Results and discussion
In fact, the dislocations are widely thought to be a non-radiative center in wurtzite GaN; they are not likely to manifest themselves by luminescence, unless point defects are trapped at them . Therefore, the most probable origin of VL is due to point defects.
From the above discussion, one can glean the obvious that the VL is related to a native point defect introduced by the indentation. Among all the native point defects in GaN, VGa appears to be the best candidate, since the transition energy from the conduction band to the 0/− transition level of VGa is estimated at about 3.15 eV , which is very close to the photon energy of VL. In addition, VGa was found to anneal out in long-range migration processes at 500 to 600 K [28, 29], which is consistent with the vanishing of VL in indented GaN after annealing at 500°C. The assignment of the VL peak to VGa is also supported by the Raman spectra, since the Raman spectra have found evidence for the existence of Ga vacancies in the indented region. Therefore, the most plausible cause for the VL is the VGa.
In conclusion, the VL band peaking at about 3.12 eV from the region near the dislocations is characterized and identified. A comprehensive study encompassing CL measurements, annealing experiments, and Raman analysis allow the assignment of VL band to e-A transitions involving VGa. A formation mechanism of vacancies by the motion of jogged dislocations is proposed to explain the dislocation luminescence in GaN single crystals under nanoindentation. The nanoscale plasticity of GaN can be better understood by considering that not only the dislocation mechanisms but also the nucleation of point defects are involved in the deformation.
Huang is currently a Postdoctoral Associate in the Center of Characterization and Analysis, SINANO, CAS. K. Xu, J. F. Wang, J. C. Zhang, and G. Q. Ren are professors in the Center of Characterization and Analysis, SINANO, CAS. Y. M. Fan is a PhD student in the Center of Characterization and Analysis, SINANO, CAS.
This work was supported by the National Natural Science Foundation of China (Grant Nos. 61306001, 61274127, 11327804, 61325022), the National Basic Research Program of China (973 Program No. 2012CB619305), the National High Technology Research and Development Program of China (863 Program) (Grant No. 2014AA032605), STS-Network Plan, CAS (KFJ-EW-STS-043), the Natural Science Foundation of Jiang Su (Grant Nos. BK2012630), and the Su Zhou International Technology Cooperation Program (Grant Nos. SH201225).
- Dadgar A, Hums C, Diez A, Blasing J, Krost A: Growth of blue GaN LED structures on 150-mm Si(111). J Crystal Growth 2006, 297: 279–282. doi:10.1016/j.jcrysgro.2006.09.032 doi:10.1016/j.jcrysgro.2006.09.032 10.1016/j.jcrysgro.2006.09.032View ArticleGoogle Scholar
- Wu YF, Saxler A, Moore M, Smith RP, Sheppard S, Chavarkar PM, Wisleder T, Mishra UK, Parikh P: 30-W/mm GaN HEMTs by field plate optimization. IEEE Electron Device Lett 2004, 25: 117. doi:10.1109/LED.2003.822667 doi:10.1109/LED.2003.822667 10.1109/LED.2003.822667View ArticleGoogle Scholar
- Nakamura S, Senoh M, Nagahama S, Iwasa N, Yamada T, Matsushita T, Kiyoku H, Sugimoto Y: InGaN-based multi-quantum-well-structure laser diodes. Jpn J Appl Phys 1996, 35: L74-L76. doi:10.1143/jjap.35.l74 doi:10.1143/jjap.35.l74 10.1143/JJAP.35.L74View ArticleGoogle Scholar
- Schall P, Cohen I, Weitz DA, Spaepen F: Visualizing dislocation nucleation by indenting colloidal crystals. Nature 2006, 440: 319–323. doi:10.1038/nature04557 doi:10.1038/nature04557 10.1038/nature04557View ArticleGoogle Scholar
- Schuh CA, Mason JK, Lund AC: Quantitative insight into dislocation nucleation from high-temperature nanoindentation experiments. Nature Mater 2005, 4: 617–621. doi:10.1038/nmat1429 doi:10.1038/nmat1429 10.1038/nmat1429View ArticleGoogle Scholar
- Huang J, Xu K, Fan YM, Niu MT, Zeng XH, Wang JF, Yang H: Nanoscale anisotropic plastic deformation in single crystal GaN. Nanoscale Res Lett 2012, 7: 150. doi:10.1186/1556–276x-7–150 doi:10.1186/1556-276x-7-150 10.1186/1556-276X-7-150View ArticleGoogle Scholar
- Bradby JE, Kucheyev SO, Williams JS, Jagadish C, Swain MV, Munroe P, Phillips MR: Indentation-induced damage in GaN epilayers. Appl Phys Lett 2002, 80: 383. doi:10.1063/1.1436280 doi:10.1063/1.1436280 10.1063/1.1436280View ArticleGoogle Scholar
- Jahn U, Trampert A, Wagner T, Brandt O, Ploog KH: Indentation of GaN: a study of the optical activity and strain state of extended defects. Phys Status Solidi A 2002, 192: 79. doi:10.1002/1521–396X(200207)192:1<79::AID-PSSA79>.0.CO;2–5 doi:10.1002/1521-396X(200207)192:1<79::AID-PSSA79>.0.CO;2-5 10.1002/1521-396X(200207)192:1<79::AID-PSSA79>3.0.CO;2-5View ArticleGoogle Scholar
- Huang J, Xu K, Gong XJ, Wang JF, Fan YM, Liu JQ, Zeng XH, Ren GQ, Zhou TF, Yang H: Dislocation cross-slip in GaN single crystals under nanoindentation. Appl Phys Lett 2011, 98: 221906. doi:10.1063/1.3593381 doi:10.1063/1.3593381 10.1063/1.3593381View ArticleGoogle Scholar
- Jian SR, Juang JY, Lai YS: Cross-sectional transmission electron microscopy observations of structural damage in Al0.16Ga0.84N thin film under contact loading. J Appl Phys 2008, 103: 033503. doi:10.1063/1.2836939 doi:10.1063/1.2836939 10.1063/1.2836939View ArticleGoogle Scholar
- Wei TB, Hu Q, Duan RF, Wang JX, Zeng YP, Li JM, Yang Y, Liu YL: Mechanical deformation behavior of nonpolar GaN thick films by Berkovich nanoindentation. Nanoscale Res Lett 2009, 4: 753–757. doi:10.1007/s11671–009–9310–1 doi:10.1007/s11671-009-9310-1 10.1007/s11671-009-9310-1View ArticleGoogle Scholar
- Jian S-R: Mechanical deformation induced in Si and GaN under Berkovich nanoindentation. Nanoscale Res Lett 2008, 3: 6–13. doi:10.1007/s11671–007–9106–0 doi:10.1007/s11671-007-9106-0 10.1007/s11671-007-9106-0View ArticleGoogle Scholar
- Puech P, Demangeot F, Frandon J, Pinquier C, Kuball M, Domnich V, Gogotsi Y: GaN nanoindentation: a micro-Raman spectroscopy study of local strain fields. J Appl Phys 2004, 96: 2853–2856. doi:10.1063/1.1775295 doi:10.1063/1.1775295 10.1063/1.1775295View ArticleGoogle Scholar
- Fujikane M, Leszczyski M, Nagao S, Nakayama T, Yamanaka S, Niihara K, Nowak R: Elastic–plastic transition during nanoindentation in bulk GaN crystal. J Alloys Compd 2008, 450: 405–411. doi:10.1016/j.jallcom.2006.10.121 doi:10.1016/j.jallcom.2006.10.121 10.1016/j.jallcom.2006.10.121View ArticleGoogle Scholar
- Shan ZW, Mishra RK, Syed Asif SA, Warren OL, Minor AM: Mechanical annealing and source-limited deformation in submicrometre-diameter Ni crystals. Nature Mater 2008, 7: 115–119. doi:10.1038/nmat2085 doi:10.1038/nmat2085 10.1038/nmat2085View ArticleGoogle Scholar
- Liu R, Bell A, Ponce FA, Chen CQ, Yang JW, Khan MA: Luminescence from stacking faults in gallium nitride. Appl Phys Lett 2005, 86: 021908. doi:10.1063/1.1852085 doi:10.1063/1.1852085 10.1063/1.1852085View ArticleGoogle Scholar
- Albrecht M, Strunk HP, Weyher JL, Grzegory I, Porowski S, Wosinski T: Carrier recombination at single dislocations in GaN measured by cathodoluminescence in a transmission electron microscope. J Appl Phys 2002, 92: 2000–2005. doi:10.1063/1.1490618 doi:10.1063/1.1490618 10.1063/1.1490618View ArticleGoogle Scholar
- Reshchikov MA, Morkoc H: Luminescence properties of defects in GaN. J Appl Phys 2005, 97: 061301. doi:10.1063/1.1868059 doi:10.1063/1.1868059 10.1063/1.1868059View ArticleGoogle Scholar
- Xu SJ, Chua SJ, Wang XC, Wang W: Observation of optically-active metastable defects in undoped GaN epilayers. Appl Phys Lett 1998, 72: 2451–2453. doi:10.1063/1.121379 doi:10.1063/1.121379 10.1063/1.121379View ArticleGoogle Scholar
- Brown SA, Reeves RJ, Haase CS, Cheung R, Kirchner C, Kamp M: Reactive-ion-etched gallium nitride: metastable defects and yellow luminescence. Appl Phys Lett 1999, 75: 3285–3287. doi:10.1063/1.125326 doi:10.1063/1.125326 10.1063/1.125326View ArticleGoogle Scholar
- Lozykowski HJ, Jadwisienczak WM, Brown I: Visible cathodoluminescence of GaN doped with Dy, Er, and Tm. Appl Phys Lett 1999, 74: 1129–1131. doi:10.1063/1.123465 doi:10.1063/1.123465 10.1063/1.123465View ArticleGoogle Scholar
- Harima H: Properties of GaN and related compounds studied by means of Raman scattering. J Phys Condens Matter 2002, 14: R967-R993. doi:10.1088/0953–8984/14/38/201 doi:10.1088/0953-8984/14/38/201 10.1088/0953-8984/14/38/201View ArticleGoogle Scholar
- Dhara S, Das CR, Hsu HC, Raj B, Bhaduri AK, Chen LC, Chen KH, Albert SK, Ray A: Recrystallization of epitaxial GaN under indentation. Appl Phys Lett 2008, 92: 143114. doi:10.1063/1.2907851 doi:10.1063/1.2907851 10.1063/1.2907851View ArticleGoogle Scholar
- Roul B, Rajpalke MK, Bhat TN, Kumar M, Kalghatgi AT, Krupanidhi SB, Kumar N, Sundaresan A: Experimental evidence of Ga-vacancy induced room temperature ferromagnetic behavior in GaN films. Appl Phys Lett 2011, 99: 162512. doi:10.1063/1.3654151 doi:10.1063/1.3654151 10.1063/1.3654151View ArticleGoogle Scholar
- Katsikini M, Papagelis K, Paloura EC, Ves S: Raman study of Mg, Si, O, and N implanted GaN. J Appl Phys 2003, 94: 4389. doi:10.1063/1.1606521 doi:10.1063/1.1606521 10.1063/1.1606521View ArticleGoogle Scholar
- Limmer W, Ritter W, Sauer R, Mensching B, Liu C, Rauschenbach B: Raman scattering in ion-implanted GaN. Appl Phys Lett 1998, 72: 2589. doi:10.1063/1.121426 doi:10.1063/1.121426 10.1063/1.121426View ArticleGoogle Scholar
- Davydov VY, Kitaev YE, Goncharuk IN, Smirnov AN, Graul J, Semchinova O, Uffmann D, Smirnov MB, Mirgorodsky AP, Evarestov RA: Phonon dispersion and Raman scattering in hexagonal GaN and AlN. Phys Rev B 1998, 58: 12899–12907. doi:10.1103/PhysRevB.58.12899 doi:10.1103/PhysRevB.58.12899 10.1103/PhysRevB.58.12899View ArticleGoogle Scholar
- Saarinen K, Suski T, Grzegory I, Look DC: Thermal stability of isolated and complexed Ga vacancies in GaN bulk crystals. Phys Rev B 2001, 64: 233201. doi:10.1103/PhysRevB.64.233201 doi:10.1103/PhysRevB.64.233201View ArticleGoogle Scholar
- Limpijumnong S, Van de Walle CG: Diffusivity of native defects in GaN. Phys Rev B 2004, 69: 035207. doi:10.1103/PhysRevB.69.035207 doi:10.1103/PhysRevB.69.035207View ArticleGoogle Scholar
- Elsner J, Jones R, Heggie MI, Sitch PK, Haugk M, Frauenheim T, Oberg S, Briddon PR: Deep acceptors trapped at threading-edge dislocations in GaN. Phys Rev B 1998, 58: 12571. doi:10.1103/PhysRevB.58.12571 doi:10.1103/PhysRevB.58.12571 10.1103/PhysRevB.58.12571View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.