A photoluminescence study of plasma reactive ion etching-induced damage in GaN

Z. Mouffak; A. Bensaoula; L. Trombetta

doi:10.1088/1674-4926/35/11/113003

J. Semicond. > 2014, Volume 35 > Issue 11 > 113003

SEMICONDUCTOR MATERIALS

A photoluminescence study of plasma reactive ion etching-induced damage in GaN

Z. Mouffak^1,, A. Bensaoula² and L. Trombetta³

+ Author Affiliations

Corresponding author: Z. Mouffak, Email:zmouffak@csufresno.edu

DOI: 10.1088/1674-4926/35/11/113003

Abstract: GaN films with reactive ion etching (RIE) induced damage were analyzed using photoluminescence (PL). We observed band-edge as well as donor-acceptor peaks with associated phonon replicas, all in agreement with previous studies. While both the control and damaged samples have their band-edge peak location change with temperature following the Varshni formula, its intensity however decreases with damage while the D-A peak increases considerably. Nitrogen post-etch plasma was shown to improve the band edge peak and decrease the D-A peak. This suggests that the N₂ plasma has helped reduce the number of trapped carriers that were participating in the D-A transition and made the D°X transition more active, which reaffirms the N₂ post-etch plasma treatment as a good technique to heal the GaN surface, most likely by filling the nitrogen vacancies previously created by etch damage.

Key words: GaN, etch damage, photoluminescence, reactive ion etching

References

[1]	Nakamura S, Mukai T, Senoh M. Candela-class high-brightness InGaN/AlGaN double-heterostructure blue-light-emitting diodes. Appl Phys Lett, 1994, 64:1687 doi: 10.1063/1.111832
[2]	Popovici G. Group Ⅲ nitride semiconductor compounds, physics and applications. Gil B, ed. Oxford:Clarendon Press, 1999
[3]	Wu Y F, Keller P B, Kapolnek D, et al. Very high breakdown voltage and large transconductance realized on GaN heterojunction field effect transistors. Appl Phys Lett, 1996, 69:1438 doi: 10.1063/1.117607
[4]	Morkoç H, Strite S, Gao G B, et al. Large-band-gap SiC, Ⅲ-Ⅴ nitride, and Ⅱ-Ⅵ ZnSe-based semiconductor device technologies. J Appl Phys, 1994, 76:1363 doi: 10.1063/1.358463
[5]	Morkoç H. Nitride semiconductors and devices. Springer, Berlin, Heidelberg:Springer Series in Material Science, 1999 doi: 10.1007/978-3-642-58562-3.pdf
[6]	Pearton S J, Vartuli C B, Zolper J C, et al. Ion implantation doping and isolation of GaN. Appl Phys Lett, 1995, 67:1435 doi: 10.1063/1.114518
[7]	Strite S, Morkoç H. GaN, AlN, and InN:a review. J Vac Sci Technol B, 1992, 10:1237 doi: 10.1116/1.585897
[8]	Goldenberg B, Zook J D, Ulmer R J. Ultraviolet and violet light-emitting GaN diodes grown by low-pressure metalorganic chemical vapor deposition. Appl Phys Lett, 1993, 62:381 doi: 10.1063/1.108963
[9]	Mouffak Z, Medelci-Djezzar N, Boney C, et al. Effect of photo-assisted RIE damage on GaN. MRS Internet J Nitride Semicond Res, 2003, 8:7 doi: 10.1557/S1092578300000508
[10]	Mouffak Z, Bensaoula A, Trombetta L. Temperature dependence of the energy gap in semiconductors. J Appl Phys, 2004, 95:727 doi: 10.1063/1.1632552
[11]	Hwang S J, Cho Y H, Song J J, et al. Photoluminescence excitation study of LO-phonon assisted excitonic transitions in GaN. MRS Proceedings, 1997, 482:691 doi: 10.1557/PROC-482-691
[12]	Fischer S, Wetzel C, Haller E E, et al. On p-type doping in GaN-acceptor binding energies. Appl Phys Lett, 1995, 67:1298 doi: 10.1063/1.114403
[13]	Götz W, Johnson N M, Chen C, et al. Activation energies of Si donors in GaN. Appl Phys Lett, 1996, 68:3144 doi: 10.1063/1.115805
[14]	Philippe A. Electro-optical characterization of hexagonal and cubic gallium nitride for blue emitters application. PhD Dissertation, Institut National des Sciences Appliquées (INSA) de Lyon, 1999
[15]	Varshni Y P. Temperature dependence of the energy gap in semiconductors. Physica, 1967, 34:149 doi: 10.1016/0031-8914(67)90062-6
[16]	Monemar B. Fundamental energy gap of GaN from photoluminescence excitation spectra. Phys Rev B, 1974, 10:676 doi: 10.1103/PhysRevB.10.676
[17]	Gil B, Briot O, Aulombard R L. Valence-band physics and the optical properties of GaN epilayers grown onto sapphire with wurtzite symmetry. Phys Rev B, 1995, 52:17028 doi: 10.1103/PhysRevB.52.R17028
[18]	Merz C, Kunzer M, Kaufmann U. Free and bound excitons in thin wurtzite GaN layers on sapphire. Semicond Sci Tech, 1996, 11:712 doi: 10.1088/0268-1242/11/5/010
[19]	Xu S J, Liu W, Li M F. Direct determination of free exciton binding energy from phonon-assisted luminescence spectra in GaN epilayers. Appl Phys Lett, 2002, 81:2959 doi: 10.1063/1.1514391

Fig. 1. Photoluminescence spectra of the control sample at 10 K. The log scale spectrum is also shown. Yellow luminescence is not very visible in this sample.

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Fig. 2. Identification of different peaks from the photoluminescence spectra of the control sample at 10 K (from Fig. 1). The log scale makes it easy to see the different recombinations.

DownLoad: Full-Size Img PowerPoint

Fig. 3. Photoluminescence spectra at different temperatures of the control part of sample A (n-GaN). We observe a red shift of the band-edge peak with increasing temperatures, due to the decrease of the bandgap with increasing temperature, and a blue shift of the D-A peak due to a thermal filling of some defect level with increasing temperatures.

DownLoad: Full-Size Img PowerPoint

Fig. 4. Photoluminescence spectra at different temperatures of the etched part of sample A. Here there is also a noticeable red shift of the band-edge peak with increasing temperatures, and there is a blue shift of the D-A peak due to a thermal filling of some defect level with increasing temperatures.

DownLoad: Full-Size Img PowerPoint

Fig. 5. Temperature dependence of the band-edge transition in the control part and the damaged part of sample A.

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Fig. 6. Temperature dependence of the donor-acceptor peak energy in the control part and damaged part of the GaN sample.

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Fig. 7. PL spectra at 14 K of a damaged sample (etched at 200 W for 20 s in BCl$_{3}$/Cl$_{2}$/N$_{2})$, a damaged sample (etched the same way) post treated with N$_{2}$ plasma, and a control sample. Damage decreases the intensity of the main peak and increases the D-A peak, which becomes more important. Post-etch N$_{2}$ plasma partially restores the band edge luminescence and decreases the defect density.

DownLoad: Full-Size Img PowerPoint

[1]	Nakamura S, Mukai T, Senoh M. Candela-class high-brightness InGaN/AlGaN double-heterostructure blue-light-emitting diodes. Appl Phys Lett, 1994, 64:1687 doi: 10.1063/1.111832
[2]	Popovici G. Group Ⅲ nitride semiconductor compounds, physics and applications. Gil B, ed. Oxford:Clarendon Press, 1999
[3]	Wu Y F, Keller P B, Kapolnek D, et al. Very high breakdown voltage and large transconductance realized on GaN heterojunction field effect transistors. Appl Phys Lett, 1996, 69:1438 doi: 10.1063/1.117607
[4]	Morkoç H, Strite S, Gao G B, et al. Large-band-gap SiC, Ⅲ-Ⅴ nitride, and Ⅱ-Ⅵ ZnSe-based semiconductor device technologies. J Appl Phys, 1994, 76:1363 doi: 10.1063/1.358463
[5]	Morkoç H. Nitride semiconductors and devices. Springer, Berlin, Heidelberg:Springer Series in Material Science, 1999 doi: 10.1007/978-3-642-58562-3.pdf
[6]	Pearton S J, Vartuli C B, Zolper J C, et al. Ion implantation doping and isolation of GaN. Appl Phys Lett, 1995, 67:1435 doi: 10.1063/1.114518
[7]	Strite S, Morkoç H. GaN, AlN, and InN:a review. J Vac Sci Technol B, 1992, 10:1237 doi: 10.1116/1.585897
[8]	Goldenberg B, Zook J D, Ulmer R J. Ultraviolet and violet light-emitting GaN diodes grown by low-pressure metalorganic chemical vapor deposition. Appl Phys Lett, 1993, 62:381 doi: 10.1063/1.108963
[9]	Mouffak Z, Medelci-Djezzar N, Boney C, et al. Effect of photo-assisted RIE damage on GaN. MRS Internet J Nitride Semicond Res, 2003, 8:7 doi: 10.1557/S1092578300000508
[10]	Mouffak Z, Bensaoula A, Trombetta L. Temperature dependence of the energy gap in semiconductors. J Appl Phys, 2004, 95:727 doi: 10.1063/1.1632552
[11]	Hwang S J, Cho Y H, Song J J, et al. Photoluminescence excitation study of LO-phonon assisted excitonic transitions in GaN. MRS Proceedings, 1997, 482:691 doi: 10.1557/PROC-482-691
[12]	Fischer S, Wetzel C, Haller E E, et al. On p-type doping in GaN-acceptor binding energies. Appl Phys Lett, 1995, 67:1298 doi: 10.1063/1.114403
[13]	Götz W, Johnson N M, Chen C, et al. Activation energies of Si donors in GaN. Appl Phys Lett, 1996, 68:3144 doi: 10.1063/1.115805
[14]	Philippe A. Electro-optical characterization of hexagonal and cubic gallium nitride for blue emitters application. PhD Dissertation, Institut National des Sciences Appliquées (INSA) de Lyon, 1999
[15]	Varshni Y P. Temperature dependence of the energy gap in semiconductors. Physica, 1967, 34:149 doi: 10.1016/0031-8914(67)90062-6
[16]	Monemar B. Fundamental energy gap of GaN from photoluminescence excitation spectra. Phys Rev B, 1974, 10:676 doi: 10.1103/PhysRevB.10.676
[17]	Gil B, Briot O, Aulombard R L. Valence-band physics and the optical properties of GaN epilayers grown onto sapphire with wurtzite symmetry. Phys Rev B, 1995, 52:17028 doi: 10.1103/PhysRevB.52.R17028
[18]	Merz C, Kunzer M, Kaufmann U. Free and bound excitons in thin wurtzite GaN layers on sapphire. Semicond Sci Tech, 1996, 11:712 doi: 10.1088/0268-1242/11/5/010
[19]	Xu S J, Liu W, Li M F. Direct determination of free exciton binding energy from phonon-assisted luminescence spectra in GaN epilayers. Appl Phys Lett, 2002, 81:2959 doi: 10.1063/1.1514391

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Received: 26 May 2014 Revised: 10 July 2014 Online: Published: 01 November 2014

GaN films with reactive ion etching (RIE) induced damage were analyzed using photoluminescence (PL). We observed band-edge as well as donor-acceptor peaks with associated phonon replicas, all in agreement with previous studies. While both the control and damaged samples have their band-edge peak location change with temperature following the Varshni formula, its intensity however decreases with damage while the D-A peak increases considerably. Nitrogen post-etch plasma was shown to improve the band edge peak and decrease the D-A peak. This suggests that the N₂ plasma has helped reduce the number of trapped carriers that were participating in the D-A transition and made the D°X transition more active, which reaffirms the N₂ post-etch plasma treatment as a good technique to heal the GaN surface, most likely by filling the nitrogen vacancies previously created by etch damage.

A photoluminescence study of plasma reactive ion etching-induced damage in GaN

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