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AlGaN multi-quantum-well structure by metalorganic vapor phase epitaxy
Journal of Crystal Growth 221 (2000) 378}381
Growth of BGaN/AlGaN multi-quantum-well structure by metalorganic vapor phase epitaxy Makoto Kurimoto*, Takayoshi Takano, Jun Yamamoto, Yoshiyuki Ishihara, Masato Horie, Mieko Tsubamoto, Hideo Kawanishi Department of Electronic Engineering, Kohgakuin University, 2665-1 Nakano-machi, Hachiohji-shi, Tokyo 192-0015, Japan
Abstract We report on the epitaxial growth and the resulting optical characteristics of B Ga N/Al Ga N multi quantum wells (MQW) grown by metalorganic vapor-phase epitaxy (MOVPE). The room-temperature photoluminescence (PL) of B Ga N/Al Ga N MQWs was observed at 360.4 nm. The calculated PL energy shift from GaN/6H-SiC was 50 meV. The PL peak energy shift resulted from a quantized energy shift (10 meV), the e!ect of boron composition (16 meV), and the e!ect of a smaller tensile residual strain along the a-axis (the e!ect of the smaller compressive residual strain along the c-axis of &0.17%) (24 meV). The emission intensity from the B Ga N/ Al Ga N MQW structure at room temperature was three-fold higher than that of the B Ga N grown directly on a 6H-SiC substrate because of the tensile strain along the a-axis in the B Ga N/Al Ga N MQW structure. 2000 Elsevier Science B.V. All rights reserved. PACS: 78.55.Ee; 78.66; 81.15.Kk Keywords: BGaN; Boron; BGaN/AlGaN MQW; PL; MOVPE; 6H-SiC
1. Introduction The BGaN ternary and related BAlGaN quaternary were proposed as possible lattice-matched systems to (0 0 0 1) 6H-SiC substrates [1]. We previously reported the growth and low-temperature photoluminescence (PL) emission of the BGaN ternary grown on a 6H-SiC substrate and also proposed its applicability to light-emitting devices operating in the UV spectral region [2, 3]. In this paper, we report the growth of B * Corresponding author. Tel.: #81-426-22-9291 (ext. 3442); fax: #81-426-25-8982. E-mail address: [email protected] (M. Kurimoto).
Ga N/Al Ga N MQWs by metal organic vapor phase epitaxy (MOVPE) and discuss their optical properties. We also discuss the e!ect of the smaller tensile residual strain along the a-axis.
2. Experimental procedure The MQW structures were grown on an AlN layer (0.5 lm) on (0 0 0 1) 6H-SiC by low-pressure MOVPE. Low-pressure MOVPE using a horizontal reactor and a #ow channel was adopted in this study [4]. Triethylboron (TEB), trimethylgallium (TMGa), trimethylaluminum (TMAl), ammonia (NH ) and monosilane (SiH ) were used as source
0022-0248/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 7 1 7 - X
M. Kurimoto et al. / Journal of Crystal Growth 221 (2000) 378}381
materials for boron, gallium, aluminum, nitrogen and silicon, respectively. The source materials were introduced into the reactor through the #ow channel with a hydrogen and nitrogen carrier gas. Layers of B Ga N and Al Ga N were used as well and barrier layers. The thicknesses of the well and barrier layers were 100 As each. The number of pairs was 25. A (GaN/AlN) bu!er layer grown using the alternating source feeding (ASF) technique [5}7] was adopted to decrease the residual tensile strain along the a-axis in the bottom layer on which the BGaN ternary was grown. The schematic diagram and the growth time sequence of the B Ga N/Al Ga N MQW struc ture are summarized in Figs. 1 and 2, respectively.
Fig. 1. Schematic diagram of the BGaN /AlGaN MQW structure.
379
3. Results The X-ray di!raction (XRD) spectrum of the MQW sample is summarized in Fig. 3. The ! 1st, 0th and 1st di!raction satellite peaks from the MQW structure are located at 2h"34.5793, 34.9343 and 35.2663 for K , respeca tively. The di!raction peak from (0 0 0 6) 6H-SiC was located at 2h"35.7273 for K . The cycle of a the MQW was estimated to be approximately 260 As (from!1st and 0th) and 280 As (from 0th and 1st). The result probably suggests that the MQW structures were fabricated with a smooth interface using 2D growth, because both cycles were generally equal. However, these cycles were not equivalent in terms of the sum of the well and barrier thicknesses of the MQW structures. Perhaps the discrepancy was caused by an increase in the initial growth rate. The room-temperature photoluminescence (PL) spectra from the MQWs structure are shown in Fig. 4. Here, the 325 nm line of a He}Cd laser was used as an excitation source. The PL peak of the B Ga N/Al Ga N MQW was observed at 360.4 nm (3.440 eV). The shift in the PL peak energy from GaN/6H-SiC was 50 meV. The emission intensity from the B Ga N/ Al Ga N MQWs structure at room temper ature was three-fold higher than that of the B Ga N grown directly on the 6H-SiC substrate. Furthermore, the peak energy of the PL spectrum from the MQW layer shifted
Fig. 2. Growth time sequence.
380
M. Kurimoto et al. / Journal of Crystal Growth 221 (2000) 378}381
4. Discussion
Fig. 3. XRD peaks of BGaN/AlGaN MQWs.
The shift in PL peak energy (50 meV) resulted from the quantized energy shift and the e!ect of the boron composition. The quantized energy shift was estimated to be approximately 10 meV, because that of the GaN/Al Ga N quantum well was approximately 10 meV [8]. On the other hand, the e!ect of boron composition on the energy shift was 16 meV, because the PL peak energy of B Ga N/6H-SiC was 16 meV higher than that of GaN/6H-SiC. We considered that the rest of the shift in PL peak energy (24 meV) was the result of the smaller tensile residual strain along the a-axis. In other words, it was the e!ect of the smaller compressive residual strain along the c-axis of &0.17%. The higher PL intensity from the B Ga N/ Al Ga N MQWs was due to carrier con"ne ment in the B Ga N wells and the improved crystal quality as a result of the smaller tensile residual strain along the a-axis in the B Ga N/Al Ga N MQWs. The BGaN based quantum well is e!ective for the fabrication of a BGaN-based laser diode. The large energy shift in B Ga N/Al Ga N may be due partly to the smaller tensile residual strain along the aaxis than that in BGaN/SiC. However, the reduced e!ective mass of B Ga N may be smaller than that of GaN, and the light e!ective mass a!ects the large quantized energy shift.
5. Conclusion
Fig. 4. PL spectra of BGaN/AlGaN MQW and BGaN/6H-SiC at room temperature.
to a higher energy than that in the B Ga N layer. The full-width at half-maximum (FWHM) of the emission peaks are almost the same at this point.
The PL peak of the B Ga N/Al Ga N MQWs was observed at 360.4 nm (3.440 eV) at room temperature. That of the emission was threefold higher than that of the B Ga N grown directly on a 6H-SiC substrate, because of reducing tensile strain along the a-axis in the B Ga N/ Al Ga N MQW structure. Acknowledgements The authors thank Professor Emeritus Y. Suematsu of the Tokyo Institute of Technology
M. Kurimoto et al. / Journal of Crystal Growth 221 (2000) 378}381
for his encouragement. We would also like to thank Dr. T. Honda of Kohgakuin University for his technical advice and comments on preparing this paper. This work was supported by Grants-In Aid (C11750020 and C11650354) from the Ministry of Education, Science, Sports and Culture, and the High-Tech Research Center in Private Universities. This work was carried out as a part of the `Research for Future Programa (JSPS-RFTF 97P00102 and JSPS-RFTF 96R16201) from the Japan Society for the Promotion of Science.
References [1] M. Haruyama, T. Shirai, H. Kawanishi, Y. Suematsu, Proceedings of the International Symposium on Blue Laser and Light Emitting Diodes, Ohmsha, Tokyo, 1996, p. 106.
381
[2] T. Honda, M. Tsubamoto, Y. Kuga, H. Kawanishi, Mat. Res. Symp. Proc. 482 (1998) 1125. [3] T. Honda, M. Shibata, M. Kurimoto, M. Tsubamoto, J. Yamamoto, H. Kawanishi, Jpn. J. Appl. Phys. 39 (2000) L2389. [4] M. Kurimoto, M. Shibata, J. Yamamoto, M. Tsubamoto, T. Honda, H. Kawanishi, J. Crystal. Growth 189/190 (1998) 189. [5] M. Kurimoto, T. Nakada, Y. Ishihara, M. Shibata, T. Takano, J. Yamamoto, T. Honda, H. Kawanishi, Phys. Stat. Sol. A 176 (1999) 665. [6] Y. Ishihara, J. Yamamoto, M. Kurimoto, T. Takano, T. Honda, H. Kawanishi, Jpn. J. Appl. Phys. 38 (1999) L1296. [7] M. Kurimoto, T. Nakada, Y. Ishihara, M. Shibata, T. Honda, H. Kawanishi, Jpn. J. Appl. Phys. 38 (1999) L551. [8] I. Akasaki, K. Hiramatsu, H. Amano, Memoirs of the Faculty of Engineering, Nagoya University, Vol. 43, 1991, p. 5.
Growth of BGaN/AlGaN multi-quantum-well structure by metalorganic vapor phase epitaxy Makoto Kurimoto*, Takayoshi Takano, Jun Yamamoto, Yoshiyuki Ishihara, Masato Horie, Mieko Tsubamoto, Hideo Kawanishi Department of Electronic Engineering, Kohgakuin University, 2665-1 Nakano-machi, Hachiohji-shi, Tokyo 192-0015, Japan
Abstract We report on the epitaxial growth and the resulting optical characteristics of B Ga N/Al Ga N multi quantum wells (MQW) grown by metalorganic vapor-phase epitaxy (MOVPE). The room-temperature photoluminescence (PL) of B Ga N/Al Ga N MQWs was observed at 360.4 nm. The calculated PL energy shift from GaN/6H-SiC was 50 meV. The PL peak energy shift resulted from a quantized energy shift (10 meV), the e!ect of boron composition (16 meV), and the e!ect of a smaller tensile residual strain along the a-axis (the e!ect of the smaller compressive residual strain along the c-axis of &0.17%) (24 meV). The emission intensity from the B Ga N/ Al Ga N MQW structure at room temperature was three-fold higher than that of the B Ga N grown directly on a 6H-SiC substrate because of the tensile strain along the a-axis in the B Ga N/Al Ga N MQW structure. 2000 Elsevier Science B.V. All rights reserved. PACS: 78.55.Ee; 78.66; 81.15.Kk Keywords: BGaN; Boron; BGaN/AlGaN MQW; PL; MOVPE; 6H-SiC
1. Introduction The BGaN ternary and related BAlGaN quaternary were proposed as possible lattice-matched systems to (0 0 0 1) 6H-SiC substrates [1]. We previously reported the growth and low-temperature photoluminescence (PL) emission of the BGaN ternary grown on a 6H-SiC substrate and also proposed its applicability to light-emitting devices operating in the UV spectral region [2, 3]. In this paper, we report the growth of B * Corresponding author. Tel.: #81-426-22-9291 (ext. 3442); fax: #81-426-25-8982. E-mail address: [email protected] (M. Kurimoto).
Ga N/Al Ga N MQWs by metal organic vapor phase epitaxy (MOVPE) and discuss their optical properties. We also discuss the e!ect of the smaller tensile residual strain along the a-axis.
2. Experimental procedure The MQW structures were grown on an AlN layer (0.5 lm) on (0 0 0 1) 6H-SiC by low-pressure MOVPE. Low-pressure MOVPE using a horizontal reactor and a #ow channel was adopted in this study [4]. Triethylboron (TEB), trimethylgallium (TMGa), trimethylaluminum (TMAl), ammonia (NH ) and monosilane (SiH ) were used as source
0022-0248/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 7 1 7 - X
M. Kurimoto et al. / Journal of Crystal Growth 221 (2000) 378}381
materials for boron, gallium, aluminum, nitrogen and silicon, respectively. The source materials were introduced into the reactor through the #ow channel with a hydrogen and nitrogen carrier gas. Layers of B Ga N and Al Ga N were used as well and barrier layers. The thicknesses of the well and barrier layers were 100 As each. The number of pairs was 25. A (GaN/AlN) bu!er layer grown using the alternating source feeding (ASF) technique [5}7] was adopted to decrease the residual tensile strain along the a-axis in the bottom layer on which the BGaN ternary was grown. The schematic diagram and the growth time sequence of the B Ga N/Al Ga N MQW struc ture are summarized in Figs. 1 and 2, respectively.
Fig. 1. Schematic diagram of the BGaN /AlGaN MQW structure.
379
3. Results The X-ray di!raction (XRD) spectrum of the MQW sample is summarized in Fig. 3. The ! 1st, 0th and 1st di!raction satellite peaks from the MQW structure are located at 2h"34.5793, 34.9343 and 35.2663 for K , respeca tively. The di!raction peak from (0 0 0 6) 6H-SiC was located at 2h"35.7273 for K . The cycle of a the MQW was estimated to be approximately 260 As (from!1st and 0th) and 280 As (from 0th and 1st). The result probably suggests that the MQW structures were fabricated with a smooth interface using 2D growth, because both cycles were generally equal. However, these cycles were not equivalent in terms of the sum of the well and barrier thicknesses of the MQW structures. Perhaps the discrepancy was caused by an increase in the initial growth rate. The room-temperature photoluminescence (PL) spectra from the MQWs structure are shown in Fig. 4. Here, the 325 nm line of a He}Cd laser was used as an excitation source. The PL peak of the B Ga N/Al Ga N MQW was observed at 360.4 nm (3.440 eV). The shift in the PL peak energy from GaN/6H-SiC was 50 meV. The emission intensity from the B Ga N/ Al Ga N MQWs structure at room temper ature was three-fold higher than that of the B Ga N grown directly on the 6H-SiC substrate. Furthermore, the peak energy of the PL spectrum from the MQW layer shifted
Fig. 2. Growth time sequence.
380
M. Kurimoto et al. / Journal of Crystal Growth 221 (2000) 378}381
4. Discussion
Fig. 3. XRD peaks of BGaN/AlGaN MQWs.
The shift in PL peak energy (50 meV) resulted from the quantized energy shift and the e!ect of the boron composition. The quantized energy shift was estimated to be approximately 10 meV, because that of the GaN/Al Ga N quantum well was approximately 10 meV [8]. On the other hand, the e!ect of boron composition on the energy shift was 16 meV, because the PL peak energy of B Ga N/6H-SiC was 16 meV higher than that of GaN/6H-SiC. We considered that the rest of the shift in PL peak energy (24 meV) was the result of the smaller tensile residual strain along the a-axis. In other words, it was the e!ect of the smaller compressive residual strain along the c-axis of &0.17%. The higher PL intensity from the B Ga N/ Al Ga N MQWs was due to carrier con"ne ment in the B Ga N wells and the improved crystal quality as a result of the smaller tensile residual strain along the a-axis in the B Ga N/Al Ga N MQWs. The BGaN based quantum well is e!ective for the fabrication of a BGaN-based laser diode. The large energy shift in B Ga N/Al Ga N may be due partly to the smaller tensile residual strain along the aaxis than that in BGaN/SiC. However, the reduced e!ective mass of B Ga N may be smaller than that of GaN, and the light e!ective mass a!ects the large quantized energy shift.
5. Conclusion
Fig. 4. PL spectra of BGaN/AlGaN MQW and BGaN/6H-SiC at room temperature.
to a higher energy than that in the B Ga N layer. The full-width at half-maximum (FWHM) of the emission peaks are almost the same at this point.
The PL peak of the B Ga N/Al Ga N MQWs was observed at 360.4 nm (3.440 eV) at room temperature. That of the emission was threefold higher than that of the B Ga N grown directly on a 6H-SiC substrate, because of reducing tensile strain along the a-axis in the B Ga N/ Al Ga N MQW structure. Acknowledgements The authors thank Professor Emeritus Y. Suematsu of the Tokyo Institute of Technology
M. Kurimoto et al. / Journal of Crystal Growth 221 (2000) 378}381
for his encouragement. We would also like to thank Dr. T. Honda of Kohgakuin University for his technical advice and comments on preparing this paper. This work was supported by Grants-In Aid (C11750020 and C11650354) from the Ministry of Education, Science, Sports and Culture, and the High-Tech Research Center in Private Universities. This work was carried out as a part of the `Research for Future Programa (JSPS-RFTF 97P00102 and JSPS-RFTF 96R16201) from the Japan Society for the Promotion of Science.
References [1] M. Haruyama, T. Shirai, H. Kawanishi, Y. Suematsu, Proceedings of the International Symposium on Blue Laser and Light Emitting Diodes, Ohmsha, Tokyo, 1996, p. 106.
381
[2] T. Honda, M. Tsubamoto, Y. Kuga, H. Kawanishi, Mat. Res. Symp. Proc. 482 (1998) 1125. [3] T. Honda, M. Shibata, M. Kurimoto, M. Tsubamoto, J. Yamamoto, H. Kawanishi, Jpn. J. Appl. Phys. 39 (2000) L2389. [4] M. Kurimoto, M. Shibata, J. Yamamoto, M. Tsubamoto, T. Honda, H. Kawanishi, J. Crystal. Growth 189/190 (1998) 189. [5] M. Kurimoto, T. Nakada, Y. Ishihara, M. Shibata, T. Takano, J. Yamamoto, T. Honda, H. Kawanishi, Phys. Stat. Sol. A 176 (1999) 665. [6] Y. Ishihara, J. Yamamoto, M. Kurimoto, T. Takano, T. Honda, H. Kawanishi, Jpn. J. Appl. Phys. 38 (1999) L1296. [7] M. Kurimoto, T. Nakada, Y. Ishihara, M. Shibata, T. Honda, H. Kawanishi, Jpn. J. Appl. Phys. 38 (1999) L551. [8] I. Akasaki, K. Hiramatsu, H. Amano, Memoirs of the Faculty of Engineering, Nagoya University, Vol. 43, 1991, p. 5.