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Synthesis of GaN phase by ion implantation
Applied Surface Science 253 (2007) 5317–5319 www.elsevier.com/locate/apsusc
Synthesis of GaN phase by ion implantation Vikas Baranwal a,*, Richa Krishna a, Fouran Singh b, Ambuj Tripathi b, Avinash C. Pandey a, Dinakar Kanjilal b b
a Department of Physics, University of Allahabad, Allahabad 211002, India Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067, India
Received 8 November 2006; received in revised form 28 November 2006; accepted 1 December 2006 Available online 3 January 2007
Abstract GaN phase is synthesized using systemic implantation of nitrogen ions of multiple energies (290, 130 and 50 keV) into Zn-doped GaAs (1 0 0) at room temperature and subsequent annealing at 850 8C for 30 min in Ar + H2 atmosphere. The implanted doses of nitrogen ions are 5 1016 and 1 1017 ions-cm 2. Glancing angle X-ray diffraction studies show that hexagonal phase of GaN were formed. The photoluminescence studies show the emission from the band edge as well as from point defects. # 2006 Elsevier B.V. All rights reserved. PACS : 61.72.Vv; 78.55.Cr; 81.05.Ea; 61.10.Nz Keywords: GaN; Ion implantation; Photoluminescence; X-ray diffraction
1. Introduction The limitations of Si and GaAs technologies at high temperatures and in radiation environments have given a niche towards the development of wide band gap semiconductors such as GaN, SiC, etc. In the recent years, GaN has been a subject of extensive research due to its importance in high temperature, high power and high frequency devices. Being a direct band gap semiconductor, it finds applications in light emitting devices acting in the full range of visible spectrum. Due to the difficulties of growing GaN in bulk, many researchers have been working on other suitable techniques for its growth. Many techniques such as rf sputtering [1], ion beam assisted deposition [2], molecular beam epitaxy [3], metal organic vapor phase epitaxy [4] have been used to grow GaN thin films on different substrates. In the present study, we have chosen ion implantation technique, which is very controlled and spatial selective. It is also having several other technological merits like electrical and optical selective area doping, electrical isolation, quantum well intermixing, etc. Nitriding by high-dose ion implantation is one of the
* Corresponding author. Tel.: +91 11 26893955; fax: +91 11 26893666. E-mail address: [email protected] (V. Baranwal). 0169-4332/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2006.12.003
approaches to create the GaN layers on the GaP [5] and GaAs [6–8] substrates. The replacement of arsenic(As) by nitrogen(N) is facilitated due to the fact that As is more volatile than Ga and tends to escape from GaAs upon thermal annealing. This technique also allows implanting N atoms into GaAs beyond solid solubility limit. In the present paper, we report the successful synthesis of GaN by high dose N-ion implantation into GaAs wafers at three energies and its post-annealing at high temperature. This work has an advantage over the work reported in reference [6] on achieving the GaN by ion beam route, in which the thickness is limited by sputter process because the energy used by them were 1–2 keV. Glancing angle X-ray diffraction (GAXRD) studies confirmed formation of the desired phase of GaN. Photoluminescence (PL) spectroscopic analysis is carried out to reconfirm the emission of luminescence from the GaN. 2. Experimental Nitrogen (N) ions are implanted into Zn-doped GaAs (1 0 0) using electron cyclotron resonance (ECR) ion source on a high voltage deck [9] at Inter-University Accelerator Centre (IUAC), New Delhi. Nitrogen ions of three different energies (290, 130 and 50 keV) are implanted at room temperature in each sample. Three different energies are used in order to create uniform
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implantation profile of N ions into GaAs in a thicker region. Two different doses of nitrogen ions were implanted into GaAs. The doses were 5 1016, 1 1017 ions-cm 2, respectively for 50 keV nitrogen ions. The doses were normalized for 130 and 290 keV nitrogen ion implantation. The normalized dose for 5 1016 was 8.2 1016 (130 keV) and 1.67 1017 (290 keV), and that for 1 1017 was 1.64 1017 (130 keV) and 3.34 1017 ions-cm 2 (290 keV). A detailed simulation of depth profile of nitrogen implantation at three energies are carried out (Fig. 1) to have nearly uniform concentration of nitrogen upto 700 nm depth. A Fortran program is used for sorting the data from the depth profile of three different energies obtained from the Transport of Ions in Matter (TRIM2003) program. The same program is also used for appending the three implantation regions. The beam current was kept at about 15 mA during implantation. Prior to the implantation, the GaAs wafer is cut into approximately 10 mm 10 mm size. These samples are then chemically cleaned using standard cleaning technique and passivated with 2% HF solution. After implantation, the samples are annealed at 850 8C for 30 min in a tubular furnace under flowing Ar + H2 (96:4) atmosphere. The samples are capped with SiO2 film of thickness 50 nm, grown by e-beam evaporation technique before annealing. The SiO2 film is deposited for the controlled evaporation of As from the GaAs surface during the thermal annealing [5]. The residual oxygen present in the furnace causes the formation of Ga2O3 or As2O3 during the annealing, since As starts evaporating from the surface of GaAs at the temperature above 6008 C. After annealing the SiO2 layer is removed using 20% HF as an etchant. XRD pattern of the as-implanted as well as annealed samples are taken with Cu Ka lines using Bruker AXS D8 advance diffractometer at IUAC, New Delhi. Photoluminescence studies are carried out using Perkin-Elmer LS55 spectrophotometer at IIT-Kharagpur. Xe lamp is used as the source of light. First, we have done PL excitation to get the wavelength for the maximum emission from the sample, which is nearly 308 nm. We have used 308 nm wavelength as an excitation wavelength for getting the emission from the sample.
Fig. 1. Simulated profile of nitrogen in GaAs for nitrogen implantation at three energies.
Fig. 2. Glancing angle XRD patterns of as-implanted samples.
3. Results and discussion The structural information of as-implanted and annealed samples is obtained using XRD analysis. In the implanted sample, we observed the broadening of the peak around GaAs peak. The broadening of the peak shows amorphization of GaAs after N ion implantation (Fig. 2). After annealing at 850 8C for 30 min recrystallization takes place and the hexagonal phase of GaN (Fig. 3) is observed. GaAs peaks after the annealing confirm that annealing results in recrystallization. In the present work [1 0 0], [1 0 1], [1 0 2] and [1 1 0] crystal planes of hexagonal GaN were observed in the annealed samples. The peaks are matched with JCPDS database. It is clear from Fig. 3 that the intensity of GaN peaks are comparable to those of GaAs, which indicates the importance of multiple energy implantation to increase the thickness of the layer. The relative intensity of GaN is dose dependent. The intensity of GaN is increased with the increasing dose of nitrogen. A few signals of Ga2O3 are also present in all the annealed samples, which have been attributed to the presence of residual oxygen during annealing in the tubular furnace. For the two set of samples PL measurement is done using Xe lamp as the light source. The excitation wavelength was 308 nm. We observed a broad band PL spectrum from 360 to
Fig. 3. Glancing angle XRD pattern of nitrogen ion implanted GaAs and annealed at 850 8C for 30 min.
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energies (290 keV, 130 keV, 50 keV) at high doses (5 1016 1 1017 ions-cm 2) into GaAs substrate at room temperature followed by furnace annealing at 850 8C for 30 min in Ar + H2 flow. Band edge emission of GaN as well as blue band photoluminescence are observed which are attributed to the formation of GaN phase by ion implantation and subsequent annealing. Acknowledgements One of the authors (V.B.) is grateful to UGC for financial assistance through UFUP project for carrying out this work. We are thankful to Low Energy Ion Beam Facility group of IUAC for providing good quality scanned beam during implantation. We are also thankful to Mr. Akhilesh Mishra for Photoluminescence measurement at IITKharagpur.
Fig. 4. Photoluminescence spectrum of nitrogen ion implanted GaAs annealed at 850 8C under flowing Ar + H2 for 30 min taken at room temperature.
375 nm, which is due to the band edge emission (Fig. 4) of GaN [10]. The broad band emission may be attributed to the implantation-induced disorder in the system. The intensity and broadening of the peak is increased with the dose. In Fig. 4 a blue band of GaN around 425 nm is observed, which extends from 411 to 429 nm. This blue band may be attributed to the point defects of GaN remains even after the annealing, which may be relatively homogeneously distributed [11]. Using TRIM calculation the order of defects is coming out to be around 1020 ions-cm 2. It is well established that in low energy ion implantation collision cascade is the prominent way of losing energy, which introduce the point defects into the system. These point defects can introduce the deep levels in the energy band. The 2.9 eV band results from the transitions involving deep level defects [12–14]. 4. Conclusion In this work hexagonal phase of GaN is synthesized successfully using nitrogen ion implantation of multiple
References [1] T. Miyazaki, K. Takada, S. Adachi, K. Ohtsuka, J. Appl. Phys. 97 (2005) 93156. [2] Y. Kang, D.C. Ingram, J. Appl. Phys. 93 (2003) 3954. [3] B. Cui, P.I. Cohen, A.M. Dabiran, J. Appl. Phys. 97 (2005) 104313. [4] P. Kozodoy, S. Keller, S.P. DenBaars, U.K. Mishra, J. Cryst. Growth 195 (1998) 265. [5] K. Kuriyama, H. Kondo, N. Hayashi, M. Ogura, M. Hasegava, N. Kobayashi, Y. Takahashi, S. Wantanabe, Appl. Phys. Lett. 79 (2001) 2546. [6] L.A. Dlouise, J. Vac. Sci. Technol. A11 (1993) 609. [7] X.W. Lin, M. Behar, R. Maltez, W. Swider, Z. Liliental Weber, J. Washburn, Appl. Phys. Lett. 67 (1995) 2699. [8] B. Boudart, J.C. Pesant, J.C. Jaeger de, P.A. Dhamelincourt, J. Raman Spectrosc. 31 (2000) 615. [9] D. Kanjilal, T. Madhu, G. Rodrigues, U.K. Rao, C.P. Safvan, A. Roy, Ind. J. Pure and Appl. Phys. 39 (2001) 25. [10] J. Petals, S. Logothetidis, S. Boultadakis, M. Alouani, J.S. Willis, Phys. Rev. B 52 (1995) 8082. [11] A. Cremades, J. Piqueras, C. Xavier, T. Monteiro, E. Pereira, B.K. Meyer, D.M. Hofman, S. Fischer, Mater. Sci. Eng. B42 (1996) 230. [12] M. Toth, K. Fleisher, M.R. Philips, Phy. Rev. B 59 (1999) 1575. [13] S.J. Xu, G. Li, S.J. Chua, X.C. Wang, W. Wang, Appl. Phys. Lett. 72 (1998) 2451. [14] M.A. Reshchikov, F. Shahedipour, R.Y. Korotkov, B.W. Wessels, M.P. Ulmer, J. Appl. Phys. 87 (2000) 3351.
Synthesis of GaN phase by ion implantation Vikas Baranwal a,*, Richa Krishna a, Fouran Singh b, Ambuj Tripathi b, Avinash C. Pandey a, Dinakar Kanjilal b b
a Department of Physics, University of Allahabad, Allahabad 211002, India Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067, India
Received 8 November 2006; received in revised form 28 November 2006; accepted 1 December 2006 Available online 3 January 2007
Abstract GaN phase is synthesized using systemic implantation of nitrogen ions of multiple energies (290, 130 and 50 keV) into Zn-doped GaAs (1 0 0) at room temperature and subsequent annealing at 850 8C for 30 min in Ar + H2 atmosphere. The implanted doses of nitrogen ions are 5 1016 and 1 1017 ions-cm 2. Glancing angle X-ray diffraction studies show that hexagonal phase of GaN were formed. The photoluminescence studies show the emission from the band edge as well as from point defects. # 2006 Elsevier B.V. All rights reserved. PACS : 61.72.Vv; 78.55.Cr; 81.05.Ea; 61.10.Nz Keywords: GaN; Ion implantation; Photoluminescence; X-ray diffraction
1. Introduction The limitations of Si and GaAs technologies at high temperatures and in radiation environments have given a niche towards the development of wide band gap semiconductors such as GaN, SiC, etc. In the recent years, GaN has been a subject of extensive research due to its importance in high temperature, high power and high frequency devices. Being a direct band gap semiconductor, it finds applications in light emitting devices acting in the full range of visible spectrum. Due to the difficulties of growing GaN in bulk, many researchers have been working on other suitable techniques for its growth. Many techniques such as rf sputtering [1], ion beam assisted deposition [2], molecular beam epitaxy [3], metal organic vapor phase epitaxy [4] have been used to grow GaN thin films on different substrates. In the present study, we have chosen ion implantation technique, which is very controlled and spatial selective. It is also having several other technological merits like electrical and optical selective area doping, electrical isolation, quantum well intermixing, etc. Nitriding by high-dose ion implantation is one of the
* Corresponding author. Tel.: +91 11 26893955; fax: +91 11 26893666. E-mail address: [email protected] (V. Baranwal). 0169-4332/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2006.12.003
approaches to create the GaN layers on the GaP [5] and GaAs [6–8] substrates. The replacement of arsenic(As) by nitrogen(N) is facilitated due to the fact that As is more volatile than Ga and tends to escape from GaAs upon thermal annealing. This technique also allows implanting N atoms into GaAs beyond solid solubility limit. In the present paper, we report the successful synthesis of GaN by high dose N-ion implantation into GaAs wafers at three energies and its post-annealing at high temperature. This work has an advantage over the work reported in reference [6] on achieving the GaN by ion beam route, in which the thickness is limited by sputter process because the energy used by them were 1–2 keV. Glancing angle X-ray diffraction (GAXRD) studies confirmed formation of the desired phase of GaN. Photoluminescence (PL) spectroscopic analysis is carried out to reconfirm the emission of luminescence from the GaN. 2. Experimental Nitrogen (N) ions are implanted into Zn-doped GaAs (1 0 0) using electron cyclotron resonance (ECR) ion source on a high voltage deck [9] at Inter-University Accelerator Centre (IUAC), New Delhi. Nitrogen ions of three different energies (290, 130 and 50 keV) are implanted at room temperature in each sample. Three different energies are used in order to create uniform
5318
V. Baranwal et al. / Applied Surface Science 253 (2007) 5317–5319
implantation profile of N ions into GaAs in a thicker region. Two different doses of nitrogen ions were implanted into GaAs. The doses were 5 1016, 1 1017 ions-cm 2, respectively for 50 keV nitrogen ions. The doses were normalized for 130 and 290 keV nitrogen ion implantation. The normalized dose for 5 1016 was 8.2 1016 (130 keV) and 1.67 1017 (290 keV), and that for 1 1017 was 1.64 1017 (130 keV) and 3.34 1017 ions-cm 2 (290 keV). A detailed simulation of depth profile of nitrogen implantation at three energies are carried out (Fig. 1) to have nearly uniform concentration of nitrogen upto 700 nm depth. A Fortran program is used for sorting the data from the depth profile of three different energies obtained from the Transport of Ions in Matter (TRIM2003) program. The same program is also used for appending the three implantation regions. The beam current was kept at about 15 mA during implantation. Prior to the implantation, the GaAs wafer is cut into approximately 10 mm 10 mm size. These samples are then chemically cleaned using standard cleaning technique and passivated with 2% HF solution. After implantation, the samples are annealed at 850 8C for 30 min in a tubular furnace under flowing Ar + H2 (96:4) atmosphere. The samples are capped with SiO2 film of thickness 50 nm, grown by e-beam evaporation technique before annealing. The SiO2 film is deposited for the controlled evaporation of As from the GaAs surface during the thermal annealing [5]. The residual oxygen present in the furnace causes the formation of Ga2O3 or As2O3 during the annealing, since As starts evaporating from the surface of GaAs at the temperature above 6008 C. After annealing the SiO2 layer is removed using 20% HF as an etchant. XRD pattern of the as-implanted as well as annealed samples are taken with Cu Ka lines using Bruker AXS D8 advance diffractometer at IUAC, New Delhi. Photoluminescence studies are carried out using Perkin-Elmer LS55 spectrophotometer at IIT-Kharagpur. Xe lamp is used as the source of light. First, we have done PL excitation to get the wavelength for the maximum emission from the sample, which is nearly 308 nm. We have used 308 nm wavelength as an excitation wavelength for getting the emission from the sample.
Fig. 1. Simulated profile of nitrogen in GaAs for nitrogen implantation at three energies.
Fig. 2. Glancing angle XRD patterns of as-implanted samples.
3. Results and discussion The structural information of as-implanted and annealed samples is obtained using XRD analysis. In the implanted sample, we observed the broadening of the peak around GaAs peak. The broadening of the peak shows amorphization of GaAs after N ion implantation (Fig. 2). After annealing at 850 8C for 30 min recrystallization takes place and the hexagonal phase of GaN (Fig. 3) is observed. GaAs peaks after the annealing confirm that annealing results in recrystallization. In the present work [1 0 0], [1 0 1], [1 0 2] and [1 1 0] crystal planes of hexagonal GaN were observed in the annealed samples. The peaks are matched with JCPDS database. It is clear from Fig. 3 that the intensity of GaN peaks are comparable to those of GaAs, which indicates the importance of multiple energy implantation to increase the thickness of the layer. The relative intensity of GaN is dose dependent. The intensity of GaN is increased with the increasing dose of nitrogen. A few signals of Ga2O3 are also present in all the annealed samples, which have been attributed to the presence of residual oxygen during annealing in the tubular furnace. For the two set of samples PL measurement is done using Xe lamp as the light source. The excitation wavelength was 308 nm. We observed a broad band PL spectrum from 360 to
Fig. 3. Glancing angle XRD pattern of nitrogen ion implanted GaAs and annealed at 850 8C for 30 min.
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energies (290 keV, 130 keV, 50 keV) at high doses (5 1016 1 1017 ions-cm 2) into GaAs substrate at room temperature followed by furnace annealing at 850 8C for 30 min in Ar + H2 flow. Band edge emission of GaN as well as blue band photoluminescence are observed which are attributed to the formation of GaN phase by ion implantation and subsequent annealing. Acknowledgements One of the authors (V.B.) is grateful to UGC for financial assistance through UFUP project for carrying out this work. We are thankful to Low Energy Ion Beam Facility group of IUAC for providing good quality scanned beam during implantation. We are also thankful to Mr. Akhilesh Mishra for Photoluminescence measurement at IITKharagpur.
Fig. 4. Photoluminescence spectrum of nitrogen ion implanted GaAs annealed at 850 8C under flowing Ar + H2 for 30 min taken at room temperature.
375 nm, which is due to the band edge emission (Fig. 4) of GaN [10]. The broad band emission may be attributed to the implantation-induced disorder in the system. The intensity and broadening of the peak is increased with the dose. In Fig. 4 a blue band of GaN around 425 nm is observed, which extends from 411 to 429 nm. This blue band may be attributed to the point defects of GaN remains even after the annealing, which may be relatively homogeneously distributed [11]. Using TRIM calculation the order of defects is coming out to be around 1020 ions-cm 2. It is well established that in low energy ion implantation collision cascade is the prominent way of losing energy, which introduce the point defects into the system. These point defects can introduce the deep levels in the energy band. The 2.9 eV band results from the transitions involving deep level defects [12–14]. 4. Conclusion In this work hexagonal phase of GaN is synthesized successfully using nitrogen ion implantation of multiple
References [1] T. Miyazaki, K. Takada, S. Adachi, K. Ohtsuka, J. Appl. Phys. 97 (2005) 93156. [2] Y. Kang, D.C. Ingram, J. Appl. Phys. 93 (2003) 3954. [3] B. Cui, P.I. Cohen, A.M. Dabiran, J. Appl. Phys. 97 (2005) 104313. [4] P. Kozodoy, S. Keller, S.P. DenBaars, U.K. Mishra, J. Cryst. Growth 195 (1998) 265. [5] K. Kuriyama, H. Kondo, N. Hayashi, M. Ogura, M. Hasegava, N. Kobayashi, Y. Takahashi, S. Wantanabe, Appl. Phys. Lett. 79 (2001) 2546. [6] L.A. Dlouise, J. Vac. Sci. Technol. A11 (1993) 609. [7] X.W. Lin, M. Behar, R. Maltez, W. Swider, Z. Liliental Weber, J. Washburn, Appl. Phys. Lett. 67 (1995) 2699. [8] B. Boudart, J.C. Pesant, J.C. Jaeger de, P.A. Dhamelincourt, J. Raman Spectrosc. 31 (2000) 615. [9] D. Kanjilal, T. Madhu, G. Rodrigues, U.K. Rao, C.P. Safvan, A. Roy, Ind. J. Pure and Appl. Phys. 39 (2001) 25. [10] J. Petals, S. Logothetidis, S. Boultadakis, M. Alouani, J.S. Willis, Phys. Rev. B 52 (1995) 8082. [11] A. Cremades, J. Piqueras, C. Xavier, T. Monteiro, E. Pereira, B.K. Meyer, D.M. Hofman, S. Fischer, Mater. Sci. Eng. B42 (1996) 230. [12] M. Toth, K. Fleisher, M.R. Philips, Phy. Rev. B 59 (1999) 1575. [13] S.J. Xu, G. Li, S.J. Chua, X.C. Wang, W. Wang, Appl. Phys. Lett. 72 (1998) 2451. [14] M.A. Reshchikov, F. Shahedipour, R.Y. Korotkov, B.W. Wessels, M.P. Ulmer, J. Appl. Phys. 87 (2000) 3351.