- Email: [email protected]
Luminescence properties of Er,O-codoped GaP grown by organometallic vapor phase epitaxy
Materials Science and Engineering B81 (2001) 153– 156 www.elsevier.com/locate/mseb
Luminescence properties of Er,O-codoped GaP grown by organometallic vapor phase epitaxy Yasufumi Fujiwara *, Tatsuhiko Koide, Yoshikazu Takeda Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Uni6ersity, Furo-cho, Chikusa-ku, Nagoya 464 -8603, Japan
Abstract We have grown Er,O-codoped GaP by organometallic vapor phase epitaxy (OMVPE) and investigated the growth conditions dependence of photoluminescence (PL) spectra due to intra-4f shell transitions of Er ions. The codoping of Er and O is performed by using an O-containing Er source, Er(DPM)3, either with or without an additional O2 flow. Several new emission lines appear by the addition of O2 into the growth ambient. Some of them are quite similar to emission lines due to an Er-2O center in Er,O-codoped GaAs. This suggests that a similar atom configuration with two O atoms is successfully formed around Er ions in GaP. The dependence of the Er-2O emission lines on growth temperature indicates the existence of a threshold growth temperature, above, which other emission lines appear. The temperature dependence of the intensity of the Er-2O emission lines reveals that thermal quenching in GaP from 23 to 300 K is smaller by about two orders in magnitude than in GaAs. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Erbium; Oxygen; GaP; Codoping; OMVPE; Atom configuration
1. Introduction Er atoms doped in III – V semiconductors and silicon exhibit sharp and temperature-stable luminescence at around 1.5 mm due to intra-4f shell transitions from the first excited state (4I13/2) to the ground state (4I15/2) of Er3 + [1]. The wavelength of 1.5 mm lies in the minimum loss region of silica fibers. However, it has been found that Er ions doped in semiconductors show various fine structures, depending on doping procedures and conditions. This indicates that various kinds of Er centers with different atom configurations are formed simultaneously in a semiconductor because the fine structures of photoluminescence (PL) spectra reflect atom configurations around Er ions. Selective formation of highly efficient Er centers for luminescence has been strongly desired for applications of Er-related luminescence to light-emitting devices. Er-doped GaP is an important material because thermal quenching of the Er-related luminescence is much * Corresponding author. Tel.: +81-52-7893368; fax: + 81-527893239. E-mail address: [email protected] (Y. Fujiwara).
smaller than in GaAs and InP [2]. We observed successfully radiant Er-related luminescence dominated by numerous extremely sharp emission lines in Er-doped GaP grown by organometallic vapor phase epitaxy (OMVPE) [3–5]. The intensity of the emission lines exhibited apparent dependence on the growth temperature, the Er concentration and the reactor pressure, indicating coexistence of various Er centers in the samples. Preliminary extended x-ray absorption fine structure (EXAFS) analysis revealed clearly substitutional incorporation of the majority of Er atoms into Ga sites in the GaP lattice, independent of the growth temperature and the Er concentration. These results indicated that Er centers responsible for the sharp emission lines involve similar substitutional Er atoms, and have different microscopic structures with native defects or impurities around the Er atoms. Oxygen has been recognized to influence strongly Er-related luminescence in semiconductors. Takahei et al. reported that the introduction of O2 into the OMVPE growth ambient produces a sharp, simple PL spectrum of Er ions in Er-doped GaAs [6]. The PL spectrum was dominated by seven emission lines under host-excited conditions at a low temperature. The Er
0921-5107/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 1 0 7 ( 0 0 ) 0 0 7 0 8 - X
154
Y. Fujiwara et al. / Materials Science and Engineering B81 (2001) 153–156
center has been identified as an Er atom located at the Ga sublattice with two adjacent O atoms (hereafter referred as Er-2O). We investigated the dependence of the PL spectra on growth temperature and found a threshold growth temperature above which the formation of the Er-2O center is greatly suppressed [7]. In this paper, we report luminescence properties of Er ions codoped with O in GaP by OMVPE using an O-containing Er source either with or without an additional O2 flow.
2. Experimental A low-pressure growth system with a vertical quartz reactor was employed in this work [8]. TMGa and TBP
were used as source materials for GaP growth. Er was doped using trisdipivaloylmethanatoerbium (Er(C11H19O2)3, Er(DPM)3) as an Er source, which contains six O atoms bonded to one Er atom in one molecule. The Er source was maintained at 40°C and introduced into the reactor by a H2 flow through an Er source cylinder. Ar gas with 50 ppm of O2 was used as an additional O source. The additional O2 content in growth ambient was changed from 0 to 0.4 ppm. The growth temperature was in the range of 550 –620°C. The substrates for the growth were undoped or S-doped (001)-oriented GaP. PL measurements were carried out mainly with the samples directly immersed in liquid He at 4.2 K. The photoexcitation source was a cw mode He-Cd laser with a beam diameter of 1 mm and an incident power of 15 mW. The luminescence of the sample was dispersed using a 0.91-m grating monochromator and detected with a liquid nitrogen-cooled Ge pin photodiode using a chopper and a lock-in amplifier. A spectral resolution of 0.3 nm in wavelength was used in this work.
3. Results and discussion
3.1. Er concentration in layers
Fig. 1. Dependence of Er concentration on the rate of a H2 flow through an Er(DPM)3 cylinder in GaP, compared with that in GaAs.
The in-depth profile and concentration of Er atoms in layers were characterized by secondary ion mass spectroscopy (SIMS) measurements. The in-depth profile of Er exhibited a uniform distribution along the growth direction in all the layers. Er concentration in the layers was calibrated using an Er-implanted GaP sample. Fig. 1 shows the dependence of Er concentration on the rate of a H2 flow through an Er source cylinder, compared with that in Er,O-codoped GaAs. The Er concentration is well controlled with the H2 flow rate in both materials. The concentration was independent of the additional O2 content in growth ambient. Furthermore, it increased slightly with the growth temperature in GaP, though it remained almost constant in Er,O-codoped GaAs [7]. At growth temperatures higher than 580°C, the Er concentration was the same in GaP and GaAs grown under identical doping conditions. As for oxygen concentration, apparent increase of oxygen signal was not clearly observed in the layers doped using Er(DPM)3 with an additional O2 flow as well as in those without the O2 flow.
3.2. Er-source dependence of PL spectra Fig. 2. 4.2 K Er-related PL spectra in GaP doped with Er using Er(DPM)3 with and without an additional O2 flow. The PL spectrum in a sample doped using an O-free Er source is also shown for comparison.
We investigated effects of Er sources on Er-related PL spectra in GaP. Fig. 2 shows the 4.2 K PL spectra in GaP doped with Er using Er(DPM)3 with and without an additional O2 flow, respectively. The PL spectra
Y. Fujiwara et al. / Materials Science and Engineering B81 (2001) 153–156
155
similar to those due to the Er-2O center, suggesting the formation of a similar atom configuration around Er ions in GaP. Peak positions of the emission lines shift to longer wavelength region in GaP, though their peak separations remain almost constant in both materials. The constant peak separation indicates that the replacement of As atoms by P atoms in the Er-2O center hardly influences the crystal-field splitting in the ground state of Er3 + . The origin of the longer-wavelength shift of peak positions is not clear at present. In Yb-doped InP, it was reported that effects of the crystal field on the ground and excited states of Yb3 + are different [9]. Therefore, a similar situation might take place for Er ions doped in semiconductors, resulting in the peak shift by the As/P replacement in the Er-2O center. Fig. 3. Comparison of 77 K Er-related PL spectra in GaP and GaAs doped with Er using Er(DPM)3 with the additional O2 Flow.
Fig. 4. Growth temperature dependence of 4.2 K Er-related PL spectra in Er,O-codoped GaP.
in a sample doped with Er using an O-free Er source (tris(methylcyclopentadienyl)erbium, Er(MeCp)3) is also shown for comparison. In the figure, letters from ‘a’ to ‘m’ are identical with those in Ref. [5]. Without the additional O2 flow, the PL spectra are basically independent of the Er sources. With the O2 flow, on the other hand, a drastic change occurs in the PL spectra. Several new emission lines (shown by single- and double-arrowheads) are observed with disappearance of some emission lines (closed circles). This result indicates a change in atom configurations around Er ions, induced by the addition of O2 into the ambient. Fig. 3 shows comparison of 77 K Er-related PL spectra in GaP and GaAs doped with Er using Er(DPM)3 with the additional O2 flow. The spectrum in GaAs is dominated by emission lines due to the Er-2O center. Some (shown by single-arrowheads in Fig. 2) of the new emission lines observed in GaP are quite
3.3. Growth conditions dependence of PL spectra The dependence of Er-related PL spectra on growth conditions was investigated systematically in samples doped using Er(DPM)3 with the additional O2 flow. The spectrum was almost independent of the Er concentration upto 3× 1018 cm − 3 and the O2 content in the growth ambient upto 0.4 ppm. However, it was greatly influenced by the growth temperature. The growth temperature dependence of the 4.2 K PL spectra is shown in Fig. 4. In growth of the samples, the H2 flow rate through the Er source and O2 content in the ambient were fixed at 125 sccm and 0.2 ppm, respectively. The PL intensity decreases with decreasing growth temperature. This behavior is in contrast with in GaAs and InP [10]. The decrease in PL intensity is due to degradation of crystal quality because the optimum growth temperature of undoped GaP is approximately 650°C for our growth system. The PL spectrum changes drastically between 580 and 600°C, suggesting that there is a threshold growth temperature. It should be noticed that the threshold growth temperature is well coincident with that in Er,O-codoped GaAs [7]. In samples grown at temperatures higher than 600°C, other new emission lines are clearly observed. This result indicates that other atom configurations around Er ions are preferentially formed above the threshold growth temperature. EXAFS analysis on the samples is now in progress to clarify the atom configurations around Er ions.
3.4. Thermal-quenching properties Thermal-quenching properties of the Er-related luminescence were investigated in Er,O-codoped GaP. Fig. 5 shows the dependence of PL spectra on measurement temperature. With increasing temperature, as mentioned above, the PL spectrum is dominated by emission lines from an Er center with an atom configuration similar to the Er-2O center in Er,O-codoped
156
Y. Fujiwara et al. / Materials Science and Engineering B81 (2001) 153–156
Fig. 5. Temperature dependence of Er-related PL spectra in Er,Ocodoped GaP. .
several new emission lines. Some of them are quite similar to emission lines due to an Er-2O center reported earlier in Er,O-codoped GaAs, indicating that a similar atom configuration with two O atoms is successfully formed around Er ions in GaP. Peak positions of the emission lines shift to longer wavelength region in GaP, though their peak separations remain almost constant in both materials. The constant peak separation suggests that the replacement of As atoms by P atoms in the Er-2O center hardly influences the crystal-field splitting in the ground state of Er3 + . The dependence of the emission lines on growth temperature reveals that there is a threshold growth temperature between 580 and 600°C. The threshold growth temperature is well coincident with that for the Er-2O emission lines in GaAs. Thermal quenching of the Er-2O lines in GaP from 23 to 300 K is smaller by about two orders in magnitude than in GaAs. This means that the Er-2O center in GaP is more useful for light-emitting devices operating at room temperature.
Acknowledgements The authors would like to thank Tri Chemical Laboratory Inc. for the Er source. The work was supported in part by Grant-in-Aids for Scientific Research of Priority Areas, Spin Controlled Semiconductor Nanostructures no. 11125209, for Scientific Research (B)(2) no. 11450119, and for Exploration Research no. 10875070 from the Ministry of Education, Science, Sports and Culture. Fig. 6. Temperature dependence of the intensity of the main emission line in Er,O-codoped GaP. The result in Er,O-codoped GaAs is also shown for comparison.
GaAs. In Fig. 6, the temperature dependence of the intensity of the main emission line (1538.5 nm) is shown together with the result for Er,O-codoped GaAs. The thermal quenching in GaP from 23 to 300 K is well coincident with that reported in Er-doped GaP without intentional O codoping [11], which is smaller by about two orders in magnitude than in GaAs. This suggests that the Er-2O center in GaP is more useful for lightemitting devices operating at room temperature.
4. Conclusion Er,O-codoped GaP has been grown by OMVPE using Er(DPM)3 either with or without an additional O2 flow, and the dependence of Er-related PL spectra on growth conditions has been investigated systematically. The addition of O2 to the growth ambient produces
References [1] For example, Mater. Res. Soc. Symp. Proc., vol. 422, 1996. [2] X.Z. Wang, B.W. Wessels, Appl. Phys. Lett. 64 (1994) 1537. [3] Y. Fujiwara, Y. Ito, Y. Nonogaki, N. Matsubara, K. Fujita, Y. Takeda, Mater. Sci. Forum 196 & 201 (1995) 621. [4] Y. Fujiwara, T. Ito, H. Ofuchi, J. Tsuchiya, A. Tanigawa, M. Tabuchi, Y. Takeda, In: M. Melloch, M. A. Reed (Eds.), Inst. Phys. Conf. Ser. No. 156, Inst. Phys. Pub., Bristol, 1998, pp. 199– 202. [5] Y. Fujiwara, A.P. Curtis, G.E. Stillman, N. Matsubara, Y. Takeda, J. Appl. Phys. 83 (1998) 4902. [6] K. Takahei, A. Taguchi, J. Appl. Phys. 74 (1994) 1979. [7] Y. Fujiwara, T. Kawamoto, T. Koide, Y. Takeda, Physica B 273– 274 (1999) 770. [8] Y. Fujiwara, S. Furuta, K. Makita, Y. Ito, Y. Nonogaki, Y. Takeda, J. Cryst. Growth 146 (1995) 544. [9] H. Ennen, G. Pomrenke, A. Axmann, J. Appl. Phys. 57 (1985) 2182. [10] Y. Fujiwara, N. Matsubara, J. Tsuchiya, T. Ito, Y. Takeda, Jpn. J. Appl. Phys. 36 (1997) 2587. [11] Y. Fujiwara, T. Ito, M. Ichida, T. Kawamoto, O. Watanabe, I. Yamakawa, A. Nakamura, Y. Takeda, Jpn. J. Appl. Phys. 38 (1999) 1008.
Luminescence properties of Er,O-codoped GaP grown by organometallic vapor phase epitaxy Yasufumi Fujiwara *, Tatsuhiko Koide, Yoshikazu Takeda Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Uni6ersity, Furo-cho, Chikusa-ku, Nagoya 464 -8603, Japan
Abstract We have grown Er,O-codoped GaP by organometallic vapor phase epitaxy (OMVPE) and investigated the growth conditions dependence of photoluminescence (PL) spectra due to intra-4f shell transitions of Er ions. The codoping of Er and O is performed by using an O-containing Er source, Er(DPM)3, either with or without an additional O2 flow. Several new emission lines appear by the addition of O2 into the growth ambient. Some of them are quite similar to emission lines due to an Er-2O center in Er,O-codoped GaAs. This suggests that a similar atom configuration with two O atoms is successfully formed around Er ions in GaP. The dependence of the Er-2O emission lines on growth temperature indicates the existence of a threshold growth temperature, above, which other emission lines appear. The temperature dependence of the intensity of the Er-2O emission lines reveals that thermal quenching in GaP from 23 to 300 K is smaller by about two orders in magnitude than in GaAs. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Erbium; Oxygen; GaP; Codoping; OMVPE; Atom configuration
1. Introduction Er atoms doped in III – V semiconductors and silicon exhibit sharp and temperature-stable luminescence at around 1.5 mm due to intra-4f shell transitions from the first excited state (4I13/2) to the ground state (4I15/2) of Er3 + [1]. The wavelength of 1.5 mm lies in the minimum loss region of silica fibers. However, it has been found that Er ions doped in semiconductors show various fine structures, depending on doping procedures and conditions. This indicates that various kinds of Er centers with different atom configurations are formed simultaneously in a semiconductor because the fine structures of photoluminescence (PL) spectra reflect atom configurations around Er ions. Selective formation of highly efficient Er centers for luminescence has been strongly desired for applications of Er-related luminescence to light-emitting devices. Er-doped GaP is an important material because thermal quenching of the Er-related luminescence is much * Corresponding author. Tel.: +81-52-7893368; fax: + 81-527893239. E-mail address: [email protected] (Y. Fujiwara).
smaller than in GaAs and InP [2]. We observed successfully radiant Er-related luminescence dominated by numerous extremely sharp emission lines in Er-doped GaP grown by organometallic vapor phase epitaxy (OMVPE) [3–5]. The intensity of the emission lines exhibited apparent dependence on the growth temperature, the Er concentration and the reactor pressure, indicating coexistence of various Er centers in the samples. Preliminary extended x-ray absorption fine structure (EXAFS) analysis revealed clearly substitutional incorporation of the majority of Er atoms into Ga sites in the GaP lattice, independent of the growth temperature and the Er concentration. These results indicated that Er centers responsible for the sharp emission lines involve similar substitutional Er atoms, and have different microscopic structures with native defects or impurities around the Er atoms. Oxygen has been recognized to influence strongly Er-related luminescence in semiconductors. Takahei et al. reported that the introduction of O2 into the OMVPE growth ambient produces a sharp, simple PL spectrum of Er ions in Er-doped GaAs [6]. The PL spectrum was dominated by seven emission lines under host-excited conditions at a low temperature. The Er
0921-5107/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 1 0 7 ( 0 0 ) 0 0 7 0 8 - X
154
Y. Fujiwara et al. / Materials Science and Engineering B81 (2001) 153–156
center has been identified as an Er atom located at the Ga sublattice with two adjacent O atoms (hereafter referred as Er-2O). We investigated the dependence of the PL spectra on growth temperature and found a threshold growth temperature above which the formation of the Er-2O center is greatly suppressed [7]. In this paper, we report luminescence properties of Er ions codoped with O in GaP by OMVPE using an O-containing Er source either with or without an additional O2 flow.
2. Experimental A low-pressure growth system with a vertical quartz reactor was employed in this work [8]. TMGa and TBP
were used as source materials for GaP growth. Er was doped using trisdipivaloylmethanatoerbium (Er(C11H19O2)3, Er(DPM)3) as an Er source, which contains six O atoms bonded to one Er atom in one molecule. The Er source was maintained at 40°C and introduced into the reactor by a H2 flow through an Er source cylinder. Ar gas with 50 ppm of O2 was used as an additional O source. The additional O2 content in growth ambient was changed from 0 to 0.4 ppm. The growth temperature was in the range of 550 –620°C. The substrates for the growth were undoped or S-doped (001)-oriented GaP. PL measurements were carried out mainly with the samples directly immersed in liquid He at 4.2 K. The photoexcitation source was a cw mode He-Cd laser with a beam diameter of 1 mm and an incident power of 15 mW. The luminescence of the sample was dispersed using a 0.91-m grating monochromator and detected with a liquid nitrogen-cooled Ge pin photodiode using a chopper and a lock-in amplifier. A spectral resolution of 0.3 nm in wavelength was used in this work.
3. Results and discussion
3.1. Er concentration in layers
Fig. 1. Dependence of Er concentration on the rate of a H2 flow through an Er(DPM)3 cylinder in GaP, compared with that in GaAs.
The in-depth profile and concentration of Er atoms in layers were characterized by secondary ion mass spectroscopy (SIMS) measurements. The in-depth profile of Er exhibited a uniform distribution along the growth direction in all the layers. Er concentration in the layers was calibrated using an Er-implanted GaP sample. Fig. 1 shows the dependence of Er concentration on the rate of a H2 flow through an Er source cylinder, compared with that in Er,O-codoped GaAs. The Er concentration is well controlled with the H2 flow rate in both materials. The concentration was independent of the additional O2 content in growth ambient. Furthermore, it increased slightly with the growth temperature in GaP, though it remained almost constant in Er,O-codoped GaAs [7]. At growth temperatures higher than 580°C, the Er concentration was the same in GaP and GaAs grown under identical doping conditions. As for oxygen concentration, apparent increase of oxygen signal was not clearly observed in the layers doped using Er(DPM)3 with an additional O2 flow as well as in those without the O2 flow.
3.2. Er-source dependence of PL spectra Fig. 2. 4.2 K Er-related PL spectra in GaP doped with Er using Er(DPM)3 with and without an additional O2 flow. The PL spectrum in a sample doped using an O-free Er source is also shown for comparison.
We investigated effects of Er sources on Er-related PL spectra in GaP. Fig. 2 shows the 4.2 K PL spectra in GaP doped with Er using Er(DPM)3 with and without an additional O2 flow, respectively. The PL spectra
Y. Fujiwara et al. / Materials Science and Engineering B81 (2001) 153–156
155
similar to those due to the Er-2O center, suggesting the formation of a similar atom configuration around Er ions in GaP. Peak positions of the emission lines shift to longer wavelength region in GaP, though their peak separations remain almost constant in both materials. The constant peak separation indicates that the replacement of As atoms by P atoms in the Er-2O center hardly influences the crystal-field splitting in the ground state of Er3 + . The origin of the longer-wavelength shift of peak positions is not clear at present. In Yb-doped InP, it was reported that effects of the crystal field on the ground and excited states of Yb3 + are different [9]. Therefore, a similar situation might take place for Er ions doped in semiconductors, resulting in the peak shift by the As/P replacement in the Er-2O center. Fig. 3. Comparison of 77 K Er-related PL spectra in GaP and GaAs doped with Er using Er(DPM)3 with the additional O2 Flow.
Fig. 4. Growth temperature dependence of 4.2 K Er-related PL spectra in Er,O-codoped GaP.
in a sample doped with Er using an O-free Er source (tris(methylcyclopentadienyl)erbium, Er(MeCp)3) is also shown for comparison. In the figure, letters from ‘a’ to ‘m’ are identical with those in Ref. [5]. Without the additional O2 flow, the PL spectra are basically independent of the Er sources. With the O2 flow, on the other hand, a drastic change occurs in the PL spectra. Several new emission lines (shown by single- and double-arrowheads) are observed with disappearance of some emission lines (closed circles). This result indicates a change in atom configurations around Er ions, induced by the addition of O2 into the ambient. Fig. 3 shows comparison of 77 K Er-related PL spectra in GaP and GaAs doped with Er using Er(DPM)3 with the additional O2 flow. The spectrum in GaAs is dominated by emission lines due to the Er-2O center. Some (shown by single-arrowheads in Fig. 2) of the new emission lines observed in GaP are quite
3.3. Growth conditions dependence of PL spectra The dependence of Er-related PL spectra on growth conditions was investigated systematically in samples doped using Er(DPM)3 with the additional O2 flow. The spectrum was almost independent of the Er concentration upto 3× 1018 cm − 3 and the O2 content in the growth ambient upto 0.4 ppm. However, it was greatly influenced by the growth temperature. The growth temperature dependence of the 4.2 K PL spectra is shown in Fig. 4. In growth of the samples, the H2 flow rate through the Er source and O2 content in the ambient were fixed at 125 sccm and 0.2 ppm, respectively. The PL intensity decreases with decreasing growth temperature. This behavior is in contrast with in GaAs and InP [10]. The decrease in PL intensity is due to degradation of crystal quality because the optimum growth temperature of undoped GaP is approximately 650°C for our growth system. The PL spectrum changes drastically between 580 and 600°C, suggesting that there is a threshold growth temperature. It should be noticed that the threshold growth temperature is well coincident with that in Er,O-codoped GaAs [7]. In samples grown at temperatures higher than 600°C, other new emission lines are clearly observed. This result indicates that other atom configurations around Er ions are preferentially formed above the threshold growth temperature. EXAFS analysis on the samples is now in progress to clarify the atom configurations around Er ions.
3.4. Thermal-quenching properties Thermal-quenching properties of the Er-related luminescence were investigated in Er,O-codoped GaP. Fig. 5 shows the dependence of PL spectra on measurement temperature. With increasing temperature, as mentioned above, the PL spectrum is dominated by emission lines from an Er center with an atom configuration similar to the Er-2O center in Er,O-codoped
156
Y. Fujiwara et al. / Materials Science and Engineering B81 (2001) 153–156
Fig. 5. Temperature dependence of Er-related PL spectra in Er,Ocodoped GaP. .
several new emission lines. Some of them are quite similar to emission lines due to an Er-2O center reported earlier in Er,O-codoped GaAs, indicating that a similar atom configuration with two O atoms is successfully formed around Er ions in GaP. Peak positions of the emission lines shift to longer wavelength region in GaP, though their peak separations remain almost constant in both materials. The constant peak separation suggests that the replacement of As atoms by P atoms in the Er-2O center hardly influences the crystal-field splitting in the ground state of Er3 + . The dependence of the emission lines on growth temperature reveals that there is a threshold growth temperature between 580 and 600°C. The threshold growth temperature is well coincident with that for the Er-2O emission lines in GaAs. Thermal quenching of the Er-2O lines in GaP from 23 to 300 K is smaller by about two orders in magnitude than in GaAs. This means that the Er-2O center in GaP is more useful for light-emitting devices operating at room temperature.
Acknowledgements The authors would like to thank Tri Chemical Laboratory Inc. for the Er source. The work was supported in part by Grant-in-Aids for Scientific Research of Priority Areas, Spin Controlled Semiconductor Nanostructures no. 11125209, for Scientific Research (B)(2) no. 11450119, and for Exploration Research no. 10875070 from the Ministry of Education, Science, Sports and Culture. Fig. 6. Temperature dependence of the intensity of the main emission line in Er,O-codoped GaP. The result in Er,O-codoped GaAs is also shown for comparison.
GaAs. In Fig. 6, the temperature dependence of the intensity of the main emission line (1538.5 nm) is shown together with the result for Er,O-codoped GaAs. The thermal quenching in GaP from 23 to 300 K is well coincident with that reported in Er-doped GaP without intentional O codoping [11], which is smaller by about two orders in magnitude than in GaAs. This suggests that the Er-2O center in GaP is more useful for lightemitting devices operating at room temperature.
4. Conclusion Er,O-codoped GaP has been grown by OMVPE using Er(DPM)3 either with or without an additional O2 flow, and the dependence of Er-related PL spectra on growth conditions has been investigated systematically. The addition of O2 to the growth ambient produces
References [1] For example, Mater. Res. Soc. Symp. Proc., vol. 422, 1996. [2] X.Z. Wang, B.W. Wessels, Appl. Phys. Lett. 64 (1994) 1537. [3] Y. Fujiwara, Y. Ito, Y. Nonogaki, N. Matsubara, K. Fujita, Y. Takeda, Mater. Sci. Forum 196 & 201 (1995) 621. [4] Y. Fujiwara, T. Ito, H. Ofuchi, J. Tsuchiya, A. Tanigawa, M. Tabuchi, Y. Takeda, In: M. Melloch, M. A. Reed (Eds.), Inst. Phys. Conf. Ser. No. 156, Inst. Phys. Pub., Bristol, 1998, pp. 199– 202. [5] Y. Fujiwara, A.P. Curtis, G.E. Stillman, N. Matsubara, Y. Takeda, J. Appl. Phys. 83 (1998) 4902. [6] K. Takahei, A. Taguchi, J. Appl. Phys. 74 (1994) 1979. [7] Y. Fujiwara, T. Kawamoto, T. Koide, Y. Takeda, Physica B 273– 274 (1999) 770. [8] Y. Fujiwara, S. Furuta, K. Makita, Y. Ito, Y. Nonogaki, Y. Takeda, J. Cryst. Growth 146 (1995) 544. [9] H. Ennen, G. Pomrenke, A. Axmann, J. Appl. Phys. 57 (1985) 2182. [10] Y. Fujiwara, N. Matsubara, J. Tsuchiya, T. Ito, Y. Takeda, Jpn. J. Appl. Phys. 36 (1997) 2587. [11] Y. Fujiwara, T. Ito, M. Ichida, T. Kawamoto, O. Watanabe, I. Yamakawa, A. Nakamura, Y. Takeda, Jpn. J. Appl. Phys. 38 (1999) 1008.