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GaAs quantum dots with an intense and narrow photoluminescence peak at 1.3μm
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Physica E 17 (2003) 127 – 128 www.elsevier.com/locate/physe
InAsN/GaAs quantum dots with an intense and narrow photoluminescence peak at 1:3 m Y.D. Janga , J.S. Yima , U.H. Leea , D. Leea;∗ , J.W. Jangb , K.H. Parkb , W.G. Jeongb , J.H. Leec , D.K. Ohc a Department
of Physics, Chungnam National University, Daejeon 305-764, South Korea of Materials Engineering, Sungkyunkwan University, Suwon, South Korea c Electronics and Telecommunications Research Institute, Daejeon 305-350, South Korea b Department
Abstract A strong and narrow photoluminescence (PL) signal with a full-width at half-maximum of 34 meV emitting at 1:3 m at room temperature has been obtained from InAsN quantum dots (QD) on GaAs. The PL yield of the 1:3 m peak at room temperature remains at 8% of the value at 10 K and the carrier lifetime at 10 K is measured to be 600 ps. We believe these values indicate that the grown InAsN QDs are of high crystal quality. ? 2002 Elsevier Science B.V. All rights reserved. PACS: 78.67.Hc; 78.55.Cr; 73.21.La Keywords: Quantum dot; Laser diode; Nitrogen
Recently, much eAort has been given for the realization of eCcient laser diodes emitting at 1:3 m on GaAs substrate. One candidate for the active medium is InGaNAs quantum wells [1] and another one is In(Ga)As quantum dots (QDs) [2,3]. Although 1:3 m lasing on GaAs substrate has already been reported, it is still not easy to grow eCcient active media. In this work, we present optical characteristics of InAsN QDs grown on GaAs substrate, which emit a narrow photoluminescence (PL) signal at 1:3 m. The incorporation of nitrogen in InAs lowers the energy gap and at the same time decreases the lattice constant [4]. This characteristic is an important advantage over an InGaAs QD system in which the energy gap ∗ Corresponding author. Tel.: +82-42-821-6274; fax: +82-42822-8011. E-mail address: [email protected] (D. Lee).
increases and so the size of QDs should be very large to achieve the 1:3 m emission. Five periods of InAsN/GaAs QDs were grown by metal-organic chemical vapor deposition. The QDs were grown at 540◦ C and the QDs layers were separated by 20 nm thick GaAs spacers. The AsH3 =III ratio was 75 and the dimethylhydrazine=AsH3 ratios of 2.7–5.7 were used to grow the QDs. The details of the QD growth will be presented elsewhere. Fig. 1 shows PL spectra at 300 K taken from the QD sample with the incorporation of nitrogen (QDN) and the QD sample without nitrogen (QD1). In contrast to the rather broad emission band at 1:2 m from QD1, the PL spectrum from QDN shows a strong and narrow PL peak with a full-width at halfmaximum (FWHM) of 34 meV at 1:30 m, and 1 a relatively weak ( 10 ×) broad peak at 1:2 m. At 10 K, the PL spectrum from QDN shows a narrow
1386-9477/03/$ - see front matter ? 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S1386-9477(02)00744-0
128
Y.D. Jang et al. / Physica E 17 (2003) 127 – 128
QD1 QDN 300 K
500
0 900
1xe7 PL Intensity (arb. units)
PL Intensity (Normalized)
1000
QDN
1xe6 1xe5 10 K 300 K
4
1xe
1000 1100 1200 1300 1400 Wavelength (nm)
0
500
1000 1500 Delay Time (ps)
2000
Fig. 1. Room temperature PL spectra from QD1 without nitrogen and QDN with nitrogen.
Fig. 2. PL decay curves taken at 10 and 300 K, from QDN.
PL peak with a FWHM of 35 meV at 1:21 m and a weaker 1:07 m broad peak ( 13 ×). The shape of the spectrum does not change with excitation power. Since the shape and relative intensity are almost the same at diAerent carrier densities, we expect that there is almost no carrier relaxation from the 1:07 m band to the 1:21 m band and almost no extrinsic localization centers. The narrow PL peak has the same PL shape and shows a typical energy shift due to the band-gap shift, with a temperature change between 10 and 300 K. However, the peak shift of the broad peak with temperature is quite large, similar to the one reported before [5]. The PL yield (wavelength integrated PL intensity) of the 1:3 m peak remains high at 300 K, at 8% of the value at 10 K, but that of the 1:2 m peak drops to 2%. The relatively high PL yield of 1:3 m PL peak may be due to the small numbers of defect centers and the less thermal activation since the energy level is relatively deep from a wetting layer or GaAs barrier. Time-resolved PL, shown in Fig. 2, is measured by a streak camera and picosecond pulses from a Ti:sapphire laser. At 10 K, the carrier lifetime at the narrow peak is around 600 ps at low excitation and lifetime change within the FWHM is not noticeable. At 300 K, the carrier decay is not fast, but comparable to the 10 K value. This implies that carrier escape from QDs due to the thermal activation or capture into defects is not signiMcant in this band. The mechanism for the narrowing of PL spectrum at 1:3 m is not clear at this moment and should be
further studied. However, the narrow FWHM and strong PL indicate that high-quality structures with a uniform size distribution and a small number of defects have been grown. The addition of nitrogen into InAs seems to improve material quality compared to the conventional QDs, since it does not require a very large dot size to achieve 1:3 m emission. As a result, the present InAsN QDs on GaAs substrate emitting at 1:3 m could be suitable for 1:3 m laser diode. In summary, InAsN/GaAs QDs emit a strong and narrow PL peak at 1:3 m. The QD system is typically easier to grow and shows better optical characteristics than other 1:3 m emitting systems on GaAs substrate. This work is supported by Korea Science and Engineering Foundation (Grant No. R01-2000-00037) and Ministry of Information and Communications (Grant No. 02MB2410) in part. References [1] K.D. Choquette, J.F. Klem, A.J. Fischer, O. Blum, A.A Allerman, I.J. Fritz, S.R. Kurtz, W.G. Breiland, R. Sieg, K.M. Geib, J.W. Scott, R.L. Naone, Electron. Lett. 36 (2000) 1388. [2] D.L. HuAaker, L.A. Graham, D.G. Deppe, Appl. Phys. Lett. 72 (1998) 214. [3] J.A. Lott, N.N. Ledentsov, V.M. Ustinov, N.A. Maleev, A.E. Zhukov, A.R. Kovsh, M.V. Maximov, B.V. Volovik, Zh.I. Alferov, D. Bimberg, Electron. Lett. 36 (2000) 1384. [4] J.S. Harris Jr., J. Korean Phys. Soc. 39 (2001) s306. [5] U.H. Lee, D. Lee, H.G. Lee, S.K. Noh, J.Y. Leem, H.J. Lee, Appl. Phys. Lett. 74 (1999) 1597.
Physica E 17 (2003) 127 – 128 www.elsevier.com/locate/physe
InAsN/GaAs quantum dots with an intense and narrow photoluminescence peak at 1:3 m Y.D. Janga , J.S. Yima , U.H. Leea , D. Leea;∗ , J.W. Jangb , K.H. Parkb , W.G. Jeongb , J.H. Leec , D.K. Ohc a Department
of Physics, Chungnam National University, Daejeon 305-764, South Korea of Materials Engineering, Sungkyunkwan University, Suwon, South Korea c Electronics and Telecommunications Research Institute, Daejeon 305-350, South Korea b Department
Abstract A strong and narrow photoluminescence (PL) signal with a full-width at half-maximum of 34 meV emitting at 1:3 m at room temperature has been obtained from InAsN quantum dots (QD) on GaAs. The PL yield of the 1:3 m peak at room temperature remains at 8% of the value at 10 K and the carrier lifetime at 10 K is measured to be 600 ps. We believe these values indicate that the grown InAsN QDs are of high crystal quality. ? 2002 Elsevier Science B.V. All rights reserved. PACS: 78.67.Hc; 78.55.Cr; 73.21.La Keywords: Quantum dot; Laser diode; Nitrogen
Recently, much eAort has been given for the realization of eCcient laser diodes emitting at 1:3 m on GaAs substrate. One candidate for the active medium is InGaNAs quantum wells [1] and another one is In(Ga)As quantum dots (QDs) [2,3]. Although 1:3 m lasing on GaAs substrate has already been reported, it is still not easy to grow eCcient active media. In this work, we present optical characteristics of InAsN QDs grown on GaAs substrate, which emit a narrow photoluminescence (PL) signal at 1:3 m. The incorporation of nitrogen in InAs lowers the energy gap and at the same time decreases the lattice constant [4]. This characteristic is an important advantage over an InGaAs QD system in which the energy gap ∗ Corresponding author. Tel.: +82-42-821-6274; fax: +82-42822-8011. E-mail address: [email protected] (D. Lee).
increases and so the size of QDs should be very large to achieve the 1:3 m emission. Five periods of InAsN/GaAs QDs were grown by metal-organic chemical vapor deposition. The QDs were grown at 540◦ C and the QDs layers were separated by 20 nm thick GaAs spacers. The AsH3 =III ratio was 75 and the dimethylhydrazine=AsH3 ratios of 2.7–5.7 were used to grow the QDs. The details of the QD growth will be presented elsewhere. Fig. 1 shows PL spectra at 300 K taken from the QD sample with the incorporation of nitrogen (QDN) and the QD sample without nitrogen (QD1). In contrast to the rather broad emission band at 1:2 m from QD1, the PL spectrum from QDN shows a strong and narrow PL peak with a full-width at halfmaximum (FWHM) of 34 meV at 1:30 m, and 1 a relatively weak ( 10 ×) broad peak at 1:2 m. At 10 K, the PL spectrum from QDN shows a narrow
1386-9477/03/$ - see front matter ? 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S1386-9477(02)00744-0
128
Y.D. Jang et al. / Physica E 17 (2003) 127 – 128
QD1 QDN 300 K
500
0 900
1xe7 PL Intensity (arb. units)
PL Intensity (Normalized)
1000
QDN
1xe6 1xe5 10 K 300 K
4
1xe
1000 1100 1200 1300 1400 Wavelength (nm)
0
500
1000 1500 Delay Time (ps)
2000
Fig. 1. Room temperature PL spectra from QD1 without nitrogen and QDN with nitrogen.
Fig. 2. PL decay curves taken at 10 and 300 K, from QDN.
PL peak with a FWHM of 35 meV at 1:21 m and a weaker 1:07 m broad peak ( 13 ×). The shape of the spectrum does not change with excitation power. Since the shape and relative intensity are almost the same at diAerent carrier densities, we expect that there is almost no carrier relaxation from the 1:07 m band to the 1:21 m band and almost no extrinsic localization centers. The narrow PL peak has the same PL shape and shows a typical energy shift due to the band-gap shift, with a temperature change between 10 and 300 K. However, the peak shift of the broad peak with temperature is quite large, similar to the one reported before [5]. The PL yield (wavelength integrated PL intensity) of the 1:3 m peak remains high at 300 K, at 8% of the value at 10 K, but that of the 1:2 m peak drops to 2%. The relatively high PL yield of 1:3 m PL peak may be due to the small numbers of defect centers and the less thermal activation since the energy level is relatively deep from a wetting layer or GaAs barrier. Time-resolved PL, shown in Fig. 2, is measured by a streak camera and picosecond pulses from a Ti:sapphire laser. At 10 K, the carrier lifetime at the narrow peak is around 600 ps at low excitation and lifetime change within the FWHM is not noticeable. At 300 K, the carrier decay is not fast, but comparable to the 10 K value. This implies that carrier escape from QDs due to the thermal activation or capture into defects is not signiMcant in this band. The mechanism for the narrowing of PL spectrum at 1:3 m is not clear at this moment and should be
further studied. However, the narrow FWHM and strong PL indicate that high-quality structures with a uniform size distribution and a small number of defects have been grown. The addition of nitrogen into InAs seems to improve material quality compared to the conventional QDs, since it does not require a very large dot size to achieve 1:3 m emission. As a result, the present InAsN QDs on GaAs substrate emitting at 1:3 m could be suitable for 1:3 m laser diode. In summary, InAsN/GaAs QDs emit a strong and narrow PL peak at 1:3 m. The QD system is typically easier to grow and shows better optical characteristics than other 1:3 m emitting systems on GaAs substrate. This work is supported by Korea Science and Engineering Foundation (Grant No. R01-2000-00037) and Ministry of Information and Communications (Grant No. 02MB2410) in part. References [1] K.D. Choquette, J.F. Klem, A.J. Fischer, O. Blum, A.A Allerman, I.J. Fritz, S.R. Kurtz, W.G. Breiland, R. Sieg, K.M. Geib, J.W. Scott, R.L. Naone, Electron. Lett. 36 (2000) 1388. [2] D.L. HuAaker, L.A. Graham, D.G. Deppe, Appl. Phys. Lett. 72 (1998) 214. [3] J.A. Lott, N.N. Ledentsov, V.M. Ustinov, N.A. Maleev, A.E. Zhukov, A.R. Kovsh, M.V. Maximov, B.V. Volovik, Zh.I. Alferov, D. Bimberg, Electron. Lett. 36 (2000) 1384. [4] J.S. Harris Jr., J. Korean Phys. Soc. 39 (2001) s306. [5] U.H. Lee, D. Lee, H.G. Lee, S.K. Noh, J.Y. Leem, H.J. Lee, Appl. Phys. Lett. 74 (1999) 1597.