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Photoluminescence study of Er-doped AlN
JOURNAL OF
LUMINESCENCE ELSEVIER
Journal
of Luminescence
72-74 (1997) 284-286
Photoluminescence
study of Er-doped AlN
X. Wua, U. H6mmerich”,*, J.D. MacKenzieb, C.R. Abernathyb, S.J. Peartonb, R.G. Wilson”, R.N. SchwartzC, J.M. Zavadad “Research Center for Optical Physics, Department of Physics, Hampton University, Hampton, VA 23668, USA ‘Department of Material Science and Engineering, University of Florida, Gainsville, FL 3261 I, USA ‘Hughes Research Laboratories, Malibu, CA 90265. USA ‘US Army Research Ofice. Research Triangle Park, NC 27709. USA
Abstract
We present a photoluminescence (PL) study of Er-doped AlN epilayer on sapphire substrate. The AlN : Er film was grown by metalorganic molecular beam epitaxy and an Er concentration of 2-5 x 10” Er/cm3 was obtained. Following the excitation of an argon ion laser at 488 nm, we observed a strong 1.54 pm Er3+ luminescence, which is quenched by only a factor of two between 15 K and room temperature. The photoluminescence excitation (PLE) spectrum, as well as PL lifetime measurement suggest that at 488 nm, Er3+ is excited through a photo-carrier mediated process. In contrast, exciting AlN : Er at - 525 nm seems to result in the direct excitation of an intra-4f transition of Er3+. Keywords:
Er; AlN; Photoluminescence
1. Introduction and experiments Erbium-doped wide band-gap semiconductors are of considerable technological interest as possible systems for developing near-infrared LEDs and laser diodes for optical communications. Previous studies have shown that the temperature quenching in Er 3 + luminescence from Er-doped semiconductors is strongly dependent on the energy gap of the host materials [l]. Consequently, wide band-gap III-nitrides may be excellent hosts for Er-doped electroluminescence devices. The first study of Er in the nitrides was conducted by Wilson et al. [2]. 1.54 pm Er3+ PL from the transition 4113,2 + 4115,2 of Er3+ was observed in *Corresponding author. Fax: (804)727-5955; e-mail: [email protected]. 0022-2313/97/$17.00 $2 1997 Elsevier Science B.V. All rights reserved PII SOO22-23 13(97)000 1O-O
GaN and AlN. In this work, PL of Er-doped AlN is studied. PLE spectrum, as well as PL lifetime measurements suggest that the Er3+ in AlN can be excited through either a carrier-mediated process or direct optical pumping into its intra-4f energy levels. The AlN : Er film used in this study was grown by metalorganic molecular beam epitaxy (MOMBE) at the University of Florida. Er was incorporated in the AlN during epitaxial growth and a concentration of 2-5 x lo9 Er/cm3 was obtained. The sample was optically excited at 488 nm using an argon ion laser and the Er3 ’ PL was dispersed with a 1 m monochromator and detected with a cooled Ge detector. For PLE measurements, an optical parametric oscillator pumped by a Qswitched Nd : YAG laser was used for the excitation source. Transients of the Er3+ PL decay were Er-implanted
X Wu et al. / Journal of Luminescence
285
72-74 (1997) 284-286
taken with a cooled Ge detector with a response time of 1 us and signal was recorded on a digital oscilloscope.
2. Results and discussion Fig. 1 shows Er 3+ PL spectra obtained from 488 nm excitation at temperatures of 15 and 300 K. The characteristic Er3+ emission band at 1.54 urn features a bandwidth of 44 cm- ’ (FWHM) at 15 K. The relatively large bandwidth, compared with those in other systems, e.g. Er : crystalline Si, 8 cm-’ [3] suggests that the Er3+ ions occupy a range of sites and the PL spectrum is inhomogeneously broadened. At 300 K the integrated Er3+ PL intensity is reduced by a factor of two. Fig. 2(a) shows PLE spectrum consisting of a broadband peaking at -475 nm and a sharp feature located at 525 nm. The 525 nm peak is tentatively identified as the intra-4f 4115,2 -+ ‘Hli,z transition of Er3+ and the broad excitation band is indicative of photocarrier-mediated processes. This PLE measurement reveals that Er3+ ions in AlN can be excited through either direct optical pumping of Er3+ levels or carriermediated processes. As these two types of excitation may selectively excite two different subsets of Er3+ ions, different Er3+ PL decay patterns are expected for the two excitation schemes. Fig. 2(b)
1
F
I
I
500
550
600
650
Wavelength (nm)
IE-3 ‘I 0.0
I 0.5
I 1.0
Time (ms) Fig. 2. (a) PLE spectrum decay curves of Er-doped tion at 525 and 536 nm.
of Er-doped AlN at 15 K and (b) PL AIN at 15 K following pulsed excita-
displays the transients of PL excited at 525 nm (the transition 411s,2--) ‘Hiliz) and 536 nm. Both decays are non-exponential with a long-lived component of -0.8 ms. The PL via a direct optical excitation at 525 nm contains less short-lived components in its decay than that excited through carrier-mediated processes, suggesting the existence of some long-lived Er3 + sites which can only be excited through a direct optical excitation into their 4f levels, Work is in progress to understand the details of the optical excitation mechanism of Er3+ in AlN : Er.
3. Summary _...._.......-.... 1450
1500
I
I
I
1550
1600
1650
Wavelength (nm) Fig. 1. PL spectra
from Er-doped
AIN at 15 and 300 K
The PL properties of AlN : Er prepared by MOMBE have been studied. The integrated PL from Er3+ at 1.54 urn was quenched by only a factor of two between 15 K and room temperature.
286
X Wu et al. /Journal
ofLuminescence
The Er3+ PL at 1.54 urn can be excited either through carrier-mediated processes or direct optical excitation into 4f levels of Er3+.
72-74 (1997) 284-286
of Florida has been partially supported by AROASSERT Grant DAAH04-95-1-0196. References
Acknowledgements The authors from Hampton University acknowledge the financial support by NASA Grant NAGW-2929 and Army Research Office Grant DAAH04-96-1-0089. The work at the University
[l] P.N. Favennec, H.L. Haridon, M. Salvi, D. Moutonnet and Y. Le Guillou, Electron. Lett. 25 (1989) 718. [2] R.G. Wilson, R.N. Schwartz, C.R. Abernathy, S.J. Pearton, N. Newman, M. Rubin, T. Fu and J.M. Zavada, Appl. Phys. Lett. 65 (1994) 992. [3] S. Coffa, F. Priolo, G. Franz& V. Bellani, A. Carnera and C. Spinella, Phys. Rev. B 48 (1993) 11 782.
LUMINESCENCE ELSEVIER
Journal
of Luminescence
72-74 (1997) 284-286
Photoluminescence
study of Er-doped AlN
X. Wua, U. H6mmerich”,*, J.D. MacKenzieb, C.R. Abernathyb, S.J. Peartonb, R.G. Wilson”, R.N. SchwartzC, J.M. Zavadad “Research Center for Optical Physics, Department of Physics, Hampton University, Hampton, VA 23668, USA ‘Department of Material Science and Engineering, University of Florida, Gainsville, FL 3261 I, USA ‘Hughes Research Laboratories, Malibu, CA 90265. USA ‘US Army Research Ofice. Research Triangle Park, NC 27709. USA
Abstract
We present a photoluminescence (PL) study of Er-doped AlN epilayer on sapphire substrate. The AlN : Er film was grown by metalorganic molecular beam epitaxy and an Er concentration of 2-5 x 10” Er/cm3 was obtained. Following the excitation of an argon ion laser at 488 nm, we observed a strong 1.54 pm Er3+ luminescence, which is quenched by only a factor of two between 15 K and room temperature. The photoluminescence excitation (PLE) spectrum, as well as PL lifetime measurement suggest that at 488 nm, Er3+ is excited through a photo-carrier mediated process. In contrast, exciting AlN : Er at - 525 nm seems to result in the direct excitation of an intra-4f transition of Er3+. Keywords:
Er; AlN; Photoluminescence
1. Introduction and experiments Erbium-doped wide band-gap semiconductors are of considerable technological interest as possible systems for developing near-infrared LEDs and laser diodes for optical communications. Previous studies have shown that the temperature quenching in Er 3 + luminescence from Er-doped semiconductors is strongly dependent on the energy gap of the host materials [l]. Consequently, wide band-gap III-nitrides may be excellent hosts for Er-doped electroluminescence devices. The first study of Er in the nitrides was conducted by Wilson et al. [2]. 1.54 pm Er3+ PL from the transition 4113,2 + 4115,2 of Er3+ was observed in *Corresponding author. Fax: (804)727-5955; e-mail: [email protected]. 0022-2313/97/$17.00 $2 1997 Elsevier Science B.V. All rights reserved PII SOO22-23 13(97)000 1O-O
GaN and AlN. In this work, PL of Er-doped AlN is studied. PLE spectrum, as well as PL lifetime measurements suggest that the Er3+ in AlN can be excited through either a carrier-mediated process or direct optical pumping into its intra-4f energy levels. The AlN : Er film used in this study was grown by metalorganic molecular beam epitaxy (MOMBE) at the University of Florida. Er was incorporated in the AlN during epitaxial growth and a concentration of 2-5 x lo9 Er/cm3 was obtained. The sample was optically excited at 488 nm using an argon ion laser and the Er3 ’ PL was dispersed with a 1 m monochromator and detected with a cooled Ge detector. For PLE measurements, an optical parametric oscillator pumped by a Qswitched Nd : YAG laser was used for the excitation source. Transients of the Er3+ PL decay were Er-implanted
X Wu et al. / Journal of Luminescence
285
72-74 (1997) 284-286
taken with a cooled Ge detector with a response time of 1 us and signal was recorded on a digital oscilloscope.
2. Results and discussion Fig. 1 shows Er 3+ PL spectra obtained from 488 nm excitation at temperatures of 15 and 300 K. The characteristic Er3+ emission band at 1.54 urn features a bandwidth of 44 cm- ’ (FWHM) at 15 K. The relatively large bandwidth, compared with those in other systems, e.g. Er : crystalline Si, 8 cm-’ [3] suggests that the Er3+ ions occupy a range of sites and the PL spectrum is inhomogeneously broadened. At 300 K the integrated Er3+ PL intensity is reduced by a factor of two. Fig. 2(a) shows PLE spectrum consisting of a broadband peaking at -475 nm and a sharp feature located at 525 nm. The 525 nm peak is tentatively identified as the intra-4f 4115,2 -+ ‘Hli,z transition of Er3+ and the broad excitation band is indicative of photocarrier-mediated processes. This PLE measurement reveals that Er3+ ions in AlN can be excited through either direct optical pumping of Er3+ levels or carriermediated processes. As these two types of excitation may selectively excite two different subsets of Er3+ ions, different Er3+ PL decay patterns are expected for the two excitation schemes. Fig. 2(b)
1
F
I
I
500
550
600
650
Wavelength (nm)
IE-3 ‘I 0.0
I 0.5
I 1.0
Time (ms) Fig. 2. (a) PLE spectrum decay curves of Er-doped tion at 525 and 536 nm.
of Er-doped AlN at 15 K and (b) PL AIN at 15 K following pulsed excita-
displays the transients of PL excited at 525 nm (the transition 411s,2--) ‘Hiliz) and 536 nm. Both decays are non-exponential with a long-lived component of -0.8 ms. The PL via a direct optical excitation at 525 nm contains less short-lived components in its decay than that excited through carrier-mediated processes, suggesting the existence of some long-lived Er3 + sites which can only be excited through a direct optical excitation into their 4f levels, Work is in progress to understand the details of the optical excitation mechanism of Er3+ in AlN : Er.
3. Summary _...._.......-.... 1450
1500
I
I
I
1550
1600
1650
Wavelength (nm) Fig. 1. PL spectra
from Er-doped
AIN at 15 and 300 K
The PL properties of AlN : Er prepared by MOMBE have been studied. The integrated PL from Er3+ at 1.54 urn was quenched by only a factor of two between 15 K and room temperature.
286
X Wu et al. /Journal
ofLuminescence
The Er3+ PL at 1.54 urn can be excited either through carrier-mediated processes or direct optical excitation into 4f levels of Er3+.
72-74 (1997) 284-286
of Florida has been partially supported by AROASSERT Grant DAAH04-95-1-0196. References
Acknowledgements The authors from Hampton University acknowledge the financial support by NASA Grant NAGW-2929 and Army Research Office Grant DAAH04-96-1-0089. The work at the University
[l] P.N. Favennec, H.L. Haridon, M. Salvi, D. Moutonnet and Y. Le Guillou, Electron. Lett. 25 (1989) 718. [2] R.G. Wilson, R.N. Schwartz, C.R. Abernathy, S.J. Pearton, N. Newman, M. Rubin, T. Fu and J.M. Zavada, Appl. Phys. Lett. 65 (1994) 992. [3] S. Coffa, F. Priolo, G. Franz& V. Bellani, A. Carnera and C. Spinella, Phys. Rev. B 48 (1993) 11 782.