- Email: [email protected]
Evidence of coupling between InAs self-assembled quantum dots in thin GaAs buffer layer
ARTICLE IN PRESS
Physica E 26 (2005) 276–280 www.elsevier.com/locate/physe
Evidence of coupling between InAs self-assembled quantum dots in thin GaAs buffer layer E.T. Choa,b, H.D. Leea, D.W. Leeb, J.I. Leeb,, S.I. Jungc, J.J. Yoonc, J.Y. Leemc, I.K. Hand,1 a Department of Electronics, Chungnam National University, Daejeon 305-764, Republic of Korea Nanosurface Group, Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea c School of Nano Engineering Institute for Nanotechnology Applications, Inje University, Kimhae 621-749, Republic of Korea d Nano Devices Research Center, Korea Institute of Science & Technology, Seoul 130-650, Republic of Korea b
Available online 21 November 2004
Abstract We have studied the optical properties of two layers of InAs self-assembled quantum dots (QDs). The QDs were separated by a GaAs barrier with thickness varied from 2.5 to 10 nm. All samples exhibited double peaks from lowtemperature photoluminescence spectra. The energy difference between two peaks shows that the origin of the double peaks is different for each sample. In case of the thin barrier thickness, the double peaks are due to the coupling of the ground states of lower and upper dots. In the thick barrier case, the double peaks originate from the ground and excited states because the barrier is thick enough to separate the double QDs. r 2004 Elsevier B.V. All rights reserved. PACS: 78.67.Hc; 81.07.Ta; 78.55.Cr Keywords: Quantum dots; Coupling; Photoluminescence; InAs; Bias voltage
1. Introduction The self-assembled quantum dot (QD) system is a unique low-dimensional electron system. The formation of dots is obtained in situ, by automatic Corresponding author. Fax: +82-42-868-5047.
E-mail addresses: [email protected] (J.I. Lee), [email protected] (I.K. Han). 1 Also correspond to
strain relaxation of the wetting layer and defect-free confinement of the electrons can be achieved. During the last decade, much attention has been devoted to the study of structural, optical, and electronic properties of self-assembled QDs. In particular, there has been many interesting studies of the transport through self-assembled QDs [1]. Recently, the coupled QD system is recognized as an important ingredient in the development of
1386-9477/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2004.08.063
ARTICLE IN PRESS E.T. Cho et al. / Physica E 26 (2005) 276–280
AE0
QD3
60
60
50
50
40
40
30
30
20
2
4
6
8
10
20
∆E1 = E1 - E 0 (m eV )
The self-assembled QDs were grown by molecular beam epitaxy with spontaneous island formation in the initial stages of the Stranski– Krastanow growth mode during the epitaxy of highly strained InAs on GaAs layers. The InAs dots were deposited at 480 1C after growth interruptions by GaAs layers grown at 560 1C. The two layers of QDs are separated by a GaAs spacer of varied thickness. It is 10 (QD1), 5 (QD2) and, 2.5 (QD3) nm. A 50 nm isolating GaAs layer terminated the QD structure. Finally, 100 nm n-type GaAs capping layer were grown for the bias-dependent PL (BDPL). Samples used in BDPL are evaporated 6 nm Au on capping layer and 40 nm Au under substrate. The PL measurements were carried out by using a standard phase lock-in technique. The 514.5 nm line of an Ar-ion laser was used as an excitation source. The luminescence signal was dispersed by an 1 m monochromator and detected with a liquid nitrogen cooled Ge-detector. The samples were mounted on the cold finger of a closed-cycle helium cryostat for temperature-dependent PL (TDPL) measurements at temperatures varying from 16 to 240 K, and BDPL measurements with bias varying from 3.8 V to 3.4 V.
Fig. 1 shows the PL spectra of QD1, QD2 and QD3 at 16 K under high excitation (a few KW/ cm). All samples exhibited double peaks from lowtemperature PL spectra. Since the average size of QDs could be different by means of the different growth time of QDs, the PL peak position of QD2 is shown to be different from that of QD1 and QD3. The energy difference (DE) between the two peaks in QD1 is about 58 meV, while it is below 30 meV, in QD2 and QD3, as shown in the inset of Fig. 1. The intersublevel spacing between ground state and excited state has been reported to be in the range of 50–80 meV [7]. We suppose that two peaks of QD1 originated from the ground state (E0) and excited state (E1) of QDs, respectively. Two peaks of QD2 and QD3 could have a different origin compared to those in QD1, since the energy separation between two peaks is quite low. It might be attributed to the coupling of ground states between upper layer and lower layer. If vertically two dots are closed-in, they do not
∆E0 = S E0- A E (m eV ) 0
2. Experimental details
3. Results and discussion
PL intensity (Arb. units)
solid-state quantum computing [2–3]. Another interesting property of the self-assembled QD is that self-aligned, multilayer dots can be grown [4]. In addition, the vertical multilayer shows more efficient quantum behavior than a single layer, due to the tunnel effect of electrons and holes, never seen with the single layer, by the coupling effect in the multilayer. The thinner the barrier thickness, the stronger the effect [5]. Also the coupling effect between vertically coupled QDs is applicable for many other applications like quantum-dot molecule [6] and so on, due to varying energy levels. In this study, we present the evidence for coupling in vertically coupled InAs QDs by using photoluminescence (PL), and show the change of energy level and optical properties in QDs.
277
Barrier Thickness (nm)
SE0
AE0
QD2 SE0
E0
E1
QD1 1.0
1.1
1.2
1.3
Photon Energy (eV) Fig. 1. Normalized PL spectra of all samples measured at 16 K. The Gaussian components of all samples (dotted) are shown in the same panel. The spectral resolution is always better than 4 meV.The inset is the energy difference between two peaks by GaAs barrier thickness.
ARTICLE IN PRESS E.T. Cho et al. / Physica E 26 (2005) 276–280
1.16 QD1
Photon Energy (eV)
have same energy level, because two electrons do not occupy the same energy level. Energy levels are divided into symmetric (SE0) and asymmetric states (AE0) by energy level splitting. Fafard et al [8]. reported that the coupling between upper dot and lower dot can be controlled by changing the spacer thickness between the QDs. We show now that the occurrence of double peaks in each sample in addition to two different thermally activated carrier transfer process explains the sigmoidal temperature dependence of the higher peak energy (SE0 and E1 in Fig. 1). As shown in Fig. 2(a), for temperatures lower than 70 K the higher peak energies of TDPL for each sample follow the Varshini law [9] with InAs parameters [10]. In comparison with the Varshini law, the E1 peak energy of QD1 rapidly decreases in the temperature range of 120–180 K. These phenomena are explained by the carrier escape [11]. Carrier escape in excited state by thermal energy is more probable than carriers in ground state. That is, the thermally activated carriers from the excited states in small QDs could be recaptured by larger QDs through the wetting layer and the matrix material. Recombination energy between conduction and valence band of excited-state decreases as temperature increases according to Varshini law. For temperatures more than 180 K, the E1 peak energy of QD1 follows the Varshinilaw again. Carrier escape of QD1 by thermal energy take place in the ground states as well as in the excited states. Fig. 2(b) shows that DE of QD1 is decreases from 120 K to 180 K, and then increases from 180 K. It is evident that the carrier escape of ground states in QD1 is beginning at 180 K. In the case of QD2 (QD3), from 90 K (70 K) to 150 K (120 K), the AE0 peak energy is almost constant and deviates from the Varshini law, and then follows the Varshini-law from 150 K (120 K). Usually, as the temperature further increases, the PL peak energy of QDs more rapidly shifts to lower energy as compared to the InAs band gap, which represents a behavior known for QD ensembles [12–15]. However, we cannot explain our results with the same mechanism, because the double peaks in QD2 (QD3) are not clarified as the ground and excited states, but as symmetric and
1.14
QD2
1.12 QD3 1.10
1.08 0
50
(a)
100 150 Temperature (K)
200
250
200
250
QD1
60
50 ∆E (mev) ∆
278
QD3
40
30
QD2 20 0 (b)
50
100 150 Temperature (K)
Fig. 2. Temperature dependences PL spectra of the (a) higher peak energies and (b) difference of two peaks measured from 16 K to 240 K. The continuous lines are calculated according to the Varshni law using the parameters of InAs and are shifted along the energy axis. QD1 (’), QD2 (m), QD3 (K).
asymmetric states at temperature below 90 K (70 K). When the excited states in QD2 (QD3) start occupying carriers in the high temperature region of 90–150 K (70 to 120 K), the asymmetric state emission is mixed with the excited state. Finally, the excited state emission is greatist at the high energy peak above 150 K (120 K). In Fig. 2 (b), E of QD2 and QD3 rapidly increases in the temperature range of 70–150 K. It is evident that the double peaks are due to the symmetric and asymmetric state emissions at low temperature,
ARTICLE IN PRESS E.T. Cho et al. / Physica E 26 (2005) 276–280
indicating the coupling between lower and upper dots in QD2 and QD3 splits the ground states into two. Fig. 3 shows the bias voltage evolution for the energy spacing between double peaks in QD1, QD2, and QD3, measured with respect to its value at T ¼ 16 K in more detail. DE of each sample is constant until a bias of 2.0 V, which is the built-in Schottky barrier height [16]. There are two distinct features observable in this plot over a bias of 2.0 V. As the bias increases over 2.0 V, DE of QD2 and QD3 increases, while that of QD1 remains nearly unchanged. Because the wave function overlap between lower and upper dots is not significant in QD1 with a distance of 10 nm between them the recombination process of the ground and excited states in lower dots (upper dots) occurrs only in the same dots. The ground and excited state energies in lower dots (upper dots) are varied by changing the bias voltage, so DE of QD1 is not varied. On the other hand, the wave function of lower and upper dots in QD2 and QD3 overlaps each other. It means that because the ground state of upper dots exists in lower energy level than that of lower dots, DE in QD2 and QD3 increases as voltage increase above 2.0 V [17]. The zero-bias energy splitting in QD2 and QD3 does not 70
279
originate from the coupling effects between lower and upper dots, but due to the size difference in relaxation of lattice mismatch between upper and lower layers, we could observe that DE increases after approaching zero, when a negative bias voltage is applied. As shown in Fig. 3, however, we could not observe a decrease of DE in QD2 and QD3. As a result, it is elucidated that the double peaks in QD2 and QD3 are identified as the symmetric and asymmetric states by means of coupling between lower and upper dots.
4. Conclusions We have studied the optical properties of two layers of InAs self-assembled QDs. The QDs were separated by a GaAs barrier with thickness varied from 2.5 to 10 nm. The double peaks in QD1 originate from the ground states and excited states because the barrier is thick enough to separate the double QDs. The double peaks in QD2 and QD3 are due to the coupling of the ground states of lower and upper dots. By using BD PL, the double peaks in QD2 and QD3 are elucidated to not originate from the bimodal size distribution of lower and upper dots but by a relaxation of lattice mismatch between the InAs QDs and GaAs barrier.
QD1
60
∆E (meV)
Reference 50
40
QD3 30
QD2
20 -4
-3
-2
-1
0
1
2
3
4
Bias Voltage (V) Fig. 3. Bias dependences PL spectra of the difference of two peaks measured at 16 K. QD1 (’), QD2 (m), QD3 (K)
[1] M.H. Son, J.H. Oh, D.Y. Jeong, D. Ahn, M.S. Jun, S.W. Hwang, J.E. Oh, L.W. Engel, Appl. Phys. Lett. 82 (2003) 1230. [2] M.S. Sherwin, A. Imamoglu, T. Montroy, Phys. Rev. A 60 (1999) 3508. [3] C.H. Bennet, D.P. DiVincenzo, Nature 404 (2000) 247. [4] G.S. Solomon, J.A. Trezza, A.F. Marshall, J.S. Harris Jr., Phys. Rev. Lett. 76 (1996) 952. [5] M. Colocci, A. Vinattieri, L. Lippi, F. Bogani, M. RosaClot S. Taddei, A. Bosacchi, S. Franchi, P. Frigeri, Appl. Phys. Lett. 74 (1999) 564. [6] W. Sheng, J.-P. Leburton, Appl. Phys. Lett. 81 (2002) 4449. [7] N.C. van der Vaart, A.T. Johnson, L.P. Kouwenhoven, D.J. Maas, W. de Jong, M.P. de Ruyter van Steveninck, A. van der Enden, C.J.P.M. Harmans, C.T. Foxon, Phys. B 189 (1993) 99.
ARTICLE IN PRESS 280
E.T. Cho et al. / Physica E 26 (2005) 276–280
[8] S. Fafard, M. Spanner, J.P. McCaffrey, Z.R. Wasilewski, Appl. Phys. Lett. 76 (2000) 2268. [9] Y.P. Varshni, Physica 34 (1967) 149. [10] Landolt–Bo¨rnstein, in: O. Madelung (Ed.), Numerical Data and Functional Relationships in Science and Technology, New Series, III/17a, Springer, Berlin, 1982, p. 297. [11] L. Brusaferri, S. Sanguinetti, E. Grilli, M. Guzzi, A. Bignazzi, F. Bogani, L. Carraresi, M. Colocci, A. Bosacchi, P. Frigeri, S. Franchi, Appl. Phys. Lett. 69 (1996) 3354. [12] Z. Ma, K. Pierz, P. Hinze, Appl. Phys. Lett. 79 (2001) 2564.
[13] U.H. Lee, D. Lee, H.G. Lee, S.K. Noh, J.Y. Leem, H.J. Lee, Appl. Phys. Lett. 74 (1999) 1597. [14] D.I. Lubyshev, P.P. Gonza´lez-Borrero, E. Marega Jr., E. Petitprez, N. La Scala Jr., P. Basmaji, Appl. Phys. Lett. 68 (1996) 205. [15] A. Polimeni, A. Patane`, M. Henini, L. Eaves, P.C. Main, Phys. Rev. B 59 (1999) 5064. [16] W.V. Schoenfeld, T. Lundstrom, P.M. Petroff, D. Gershoni, Appl. Phys. Lett. 74 (1999) 2194. [17] H. Htoon, J.W. Keto, O. Baklenov, A.L. Holmes Jr., C.K. Shin, Appl. Phys. Lett. 76 (2000) 700.
Physica E 26 (2005) 276–280 www.elsevier.com/locate/physe
Evidence of coupling between InAs self-assembled quantum dots in thin GaAs buffer layer E.T. Choa,b, H.D. Leea, D.W. Leeb, J.I. Leeb,, S.I. Jungc, J.J. Yoonc, J.Y. Leemc, I.K. Hand,1 a Department of Electronics, Chungnam National University, Daejeon 305-764, Republic of Korea Nanosurface Group, Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea c School of Nano Engineering Institute for Nanotechnology Applications, Inje University, Kimhae 621-749, Republic of Korea d Nano Devices Research Center, Korea Institute of Science & Technology, Seoul 130-650, Republic of Korea b
Available online 21 November 2004
Abstract We have studied the optical properties of two layers of InAs self-assembled quantum dots (QDs). The QDs were separated by a GaAs barrier with thickness varied from 2.5 to 10 nm. All samples exhibited double peaks from lowtemperature photoluminescence spectra. The energy difference between two peaks shows that the origin of the double peaks is different for each sample. In case of the thin barrier thickness, the double peaks are due to the coupling of the ground states of lower and upper dots. In the thick barrier case, the double peaks originate from the ground and excited states because the barrier is thick enough to separate the double QDs. r 2004 Elsevier B.V. All rights reserved. PACS: 78.67.Hc; 81.07.Ta; 78.55.Cr Keywords: Quantum dots; Coupling; Photoluminescence; InAs; Bias voltage
1. Introduction The self-assembled quantum dot (QD) system is a unique low-dimensional electron system. The formation of dots is obtained in situ, by automatic Corresponding author. Fax: +82-42-868-5047.
E-mail addresses: [email protected] (J.I. Lee), [email protected] (I.K. Han). 1 Also correspond to
strain relaxation of the wetting layer and defect-free confinement of the electrons can be achieved. During the last decade, much attention has been devoted to the study of structural, optical, and electronic properties of self-assembled QDs. In particular, there has been many interesting studies of the transport through self-assembled QDs [1]. Recently, the coupled QD system is recognized as an important ingredient in the development of
1386-9477/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2004.08.063
ARTICLE IN PRESS E.T. Cho et al. / Physica E 26 (2005) 276–280
AE0
QD3
60
60
50
50
40
40
30
30
20
2
4
6
8
10
20
∆E1 = E1 - E 0 (m eV )
The self-assembled QDs were grown by molecular beam epitaxy with spontaneous island formation in the initial stages of the Stranski– Krastanow growth mode during the epitaxy of highly strained InAs on GaAs layers. The InAs dots were deposited at 480 1C after growth interruptions by GaAs layers grown at 560 1C. The two layers of QDs are separated by a GaAs spacer of varied thickness. It is 10 (QD1), 5 (QD2) and, 2.5 (QD3) nm. A 50 nm isolating GaAs layer terminated the QD structure. Finally, 100 nm n-type GaAs capping layer were grown for the bias-dependent PL (BDPL). Samples used in BDPL are evaporated 6 nm Au on capping layer and 40 nm Au under substrate. The PL measurements were carried out by using a standard phase lock-in technique. The 514.5 nm line of an Ar-ion laser was used as an excitation source. The luminescence signal was dispersed by an 1 m monochromator and detected with a liquid nitrogen cooled Ge-detector. The samples were mounted on the cold finger of a closed-cycle helium cryostat for temperature-dependent PL (TDPL) measurements at temperatures varying from 16 to 240 K, and BDPL measurements with bias varying from 3.8 V to 3.4 V.
Fig. 1 shows the PL spectra of QD1, QD2 and QD3 at 16 K under high excitation (a few KW/ cm). All samples exhibited double peaks from lowtemperature PL spectra. Since the average size of QDs could be different by means of the different growth time of QDs, the PL peak position of QD2 is shown to be different from that of QD1 and QD3. The energy difference (DE) between the two peaks in QD1 is about 58 meV, while it is below 30 meV, in QD2 and QD3, as shown in the inset of Fig. 1. The intersublevel spacing between ground state and excited state has been reported to be in the range of 50–80 meV [7]. We suppose that two peaks of QD1 originated from the ground state (E0) and excited state (E1) of QDs, respectively. Two peaks of QD2 and QD3 could have a different origin compared to those in QD1, since the energy separation between two peaks is quite low. It might be attributed to the coupling of ground states between upper layer and lower layer. If vertically two dots are closed-in, they do not
∆E0 = S E0- A E (m eV ) 0
2. Experimental details
3. Results and discussion
PL intensity (Arb. units)
solid-state quantum computing [2–3]. Another interesting property of the self-assembled QD is that self-aligned, multilayer dots can be grown [4]. In addition, the vertical multilayer shows more efficient quantum behavior than a single layer, due to the tunnel effect of electrons and holes, never seen with the single layer, by the coupling effect in the multilayer. The thinner the barrier thickness, the stronger the effect [5]. Also the coupling effect between vertically coupled QDs is applicable for many other applications like quantum-dot molecule [6] and so on, due to varying energy levels. In this study, we present the evidence for coupling in vertically coupled InAs QDs by using photoluminescence (PL), and show the change of energy level and optical properties in QDs.
277
Barrier Thickness (nm)
SE0
AE0
QD2 SE0
E0
E1
QD1 1.0
1.1
1.2
1.3
Photon Energy (eV) Fig. 1. Normalized PL spectra of all samples measured at 16 K. The Gaussian components of all samples (dotted) are shown in the same panel. The spectral resolution is always better than 4 meV.The inset is the energy difference between two peaks by GaAs barrier thickness.
ARTICLE IN PRESS E.T. Cho et al. / Physica E 26 (2005) 276–280
1.16 QD1
Photon Energy (eV)
have same energy level, because two electrons do not occupy the same energy level. Energy levels are divided into symmetric (SE0) and asymmetric states (AE0) by energy level splitting. Fafard et al [8]. reported that the coupling between upper dot and lower dot can be controlled by changing the spacer thickness between the QDs. We show now that the occurrence of double peaks in each sample in addition to two different thermally activated carrier transfer process explains the sigmoidal temperature dependence of the higher peak energy (SE0 and E1 in Fig. 1). As shown in Fig. 2(a), for temperatures lower than 70 K the higher peak energies of TDPL for each sample follow the Varshini law [9] with InAs parameters [10]. In comparison with the Varshini law, the E1 peak energy of QD1 rapidly decreases in the temperature range of 120–180 K. These phenomena are explained by the carrier escape [11]. Carrier escape in excited state by thermal energy is more probable than carriers in ground state. That is, the thermally activated carriers from the excited states in small QDs could be recaptured by larger QDs through the wetting layer and the matrix material. Recombination energy between conduction and valence band of excited-state decreases as temperature increases according to Varshini law. For temperatures more than 180 K, the E1 peak energy of QD1 follows the Varshinilaw again. Carrier escape of QD1 by thermal energy take place in the ground states as well as in the excited states. Fig. 2(b) shows that DE of QD1 is decreases from 120 K to 180 K, and then increases from 180 K. It is evident that the carrier escape of ground states in QD1 is beginning at 180 K. In the case of QD2 (QD3), from 90 K (70 K) to 150 K (120 K), the AE0 peak energy is almost constant and deviates from the Varshini law, and then follows the Varshini-law from 150 K (120 K). Usually, as the temperature further increases, the PL peak energy of QDs more rapidly shifts to lower energy as compared to the InAs band gap, which represents a behavior known for QD ensembles [12–15]. However, we cannot explain our results with the same mechanism, because the double peaks in QD2 (QD3) are not clarified as the ground and excited states, but as symmetric and
1.14
QD2
1.12 QD3 1.10
1.08 0
50
(a)
100 150 Temperature (K)
200
250
200
250
QD1
60
50 ∆E (mev) ∆
278
QD3
40
30
QD2 20 0 (b)
50
100 150 Temperature (K)
Fig. 2. Temperature dependences PL spectra of the (a) higher peak energies and (b) difference of two peaks measured from 16 K to 240 K. The continuous lines are calculated according to the Varshni law using the parameters of InAs and are shifted along the energy axis. QD1 (’), QD2 (m), QD3 (K).
asymmetric states at temperature below 90 K (70 K). When the excited states in QD2 (QD3) start occupying carriers in the high temperature region of 90–150 K (70 to 120 K), the asymmetric state emission is mixed with the excited state. Finally, the excited state emission is greatist at the high energy peak above 150 K (120 K). In Fig. 2 (b), E of QD2 and QD3 rapidly increases in the temperature range of 70–150 K. It is evident that the double peaks are due to the symmetric and asymmetric state emissions at low temperature,
ARTICLE IN PRESS E.T. Cho et al. / Physica E 26 (2005) 276–280
indicating the coupling between lower and upper dots in QD2 and QD3 splits the ground states into two. Fig. 3 shows the bias voltage evolution for the energy spacing between double peaks in QD1, QD2, and QD3, measured with respect to its value at T ¼ 16 K in more detail. DE of each sample is constant until a bias of 2.0 V, which is the built-in Schottky barrier height [16]. There are two distinct features observable in this plot over a bias of 2.0 V. As the bias increases over 2.0 V, DE of QD2 and QD3 increases, while that of QD1 remains nearly unchanged. Because the wave function overlap between lower and upper dots is not significant in QD1 with a distance of 10 nm between them the recombination process of the ground and excited states in lower dots (upper dots) occurrs only in the same dots. The ground and excited state energies in lower dots (upper dots) are varied by changing the bias voltage, so DE of QD1 is not varied. On the other hand, the wave function of lower and upper dots in QD2 and QD3 overlaps each other. It means that because the ground state of upper dots exists in lower energy level than that of lower dots, DE in QD2 and QD3 increases as voltage increase above 2.0 V [17]. The zero-bias energy splitting in QD2 and QD3 does not 70
279
originate from the coupling effects between lower and upper dots, but due to the size difference in relaxation of lattice mismatch between upper and lower layers, we could observe that DE increases after approaching zero, when a negative bias voltage is applied. As shown in Fig. 3, however, we could not observe a decrease of DE in QD2 and QD3. As a result, it is elucidated that the double peaks in QD2 and QD3 are identified as the symmetric and asymmetric states by means of coupling between lower and upper dots.
4. Conclusions We have studied the optical properties of two layers of InAs self-assembled QDs. The QDs were separated by a GaAs barrier with thickness varied from 2.5 to 10 nm. The double peaks in QD1 originate from the ground states and excited states because the barrier is thick enough to separate the double QDs. The double peaks in QD2 and QD3 are due to the coupling of the ground states of lower and upper dots. By using BD PL, the double peaks in QD2 and QD3 are elucidated to not originate from the bimodal size distribution of lower and upper dots but by a relaxation of lattice mismatch between the InAs QDs and GaAs barrier.
QD1
60
∆E (meV)
Reference 50
40
QD3 30
QD2
20 -4
-3
-2
-1
0
1
2
3
4
Bias Voltage (V) Fig. 3. Bias dependences PL spectra of the difference of two peaks measured at 16 K. QD1 (’), QD2 (m), QD3 (K)
[1] M.H. Son, J.H. Oh, D.Y. Jeong, D. Ahn, M.S. Jun, S.W. Hwang, J.E. Oh, L.W. Engel, Appl. Phys. Lett. 82 (2003) 1230. [2] M.S. Sherwin, A. Imamoglu, T. Montroy, Phys. Rev. A 60 (1999) 3508. [3] C.H. Bennet, D.P. DiVincenzo, Nature 404 (2000) 247. [4] G.S. Solomon, J.A. Trezza, A.F. Marshall, J.S. Harris Jr., Phys. Rev. Lett. 76 (1996) 952. [5] M. Colocci, A. Vinattieri, L. Lippi, F. Bogani, M. RosaClot S. Taddei, A. Bosacchi, S. Franchi, P. Frigeri, Appl. Phys. Lett. 74 (1999) 564. [6] W. Sheng, J.-P. Leburton, Appl. Phys. Lett. 81 (2002) 4449. [7] N.C. van der Vaart, A.T. Johnson, L.P. Kouwenhoven, D.J. Maas, W. de Jong, M.P. de Ruyter van Steveninck, A. van der Enden, C.J.P.M. Harmans, C.T. Foxon, Phys. B 189 (1993) 99.
ARTICLE IN PRESS 280
E.T. Cho et al. / Physica E 26 (2005) 276–280
[8] S. Fafard, M. Spanner, J.P. McCaffrey, Z.R. Wasilewski, Appl. Phys. Lett. 76 (2000) 2268. [9] Y.P. Varshni, Physica 34 (1967) 149. [10] Landolt–Bo¨rnstein, in: O. Madelung (Ed.), Numerical Data and Functional Relationships in Science and Technology, New Series, III/17a, Springer, Berlin, 1982, p. 297. [11] L. Brusaferri, S. Sanguinetti, E. Grilli, M. Guzzi, A. Bignazzi, F. Bogani, L. Carraresi, M. Colocci, A. Bosacchi, P. Frigeri, S. Franchi, Appl. Phys. Lett. 69 (1996) 3354. [12] Z. Ma, K. Pierz, P. Hinze, Appl. Phys. Lett. 79 (2001) 2564.
[13] U.H. Lee, D. Lee, H.G. Lee, S.K. Noh, J.Y. Leem, H.J. Lee, Appl. Phys. Lett. 74 (1999) 1597. [14] D.I. Lubyshev, P.P. Gonza´lez-Borrero, E. Marega Jr., E. Petitprez, N. La Scala Jr., P. Basmaji, Appl. Phys. Lett. 68 (1996) 205. [15] A. Polimeni, A. Patane`, M. Henini, L. Eaves, P.C. Main, Phys. Rev. B 59 (1999) 5064. [16] W.V. Schoenfeld, T. Lundstrom, P.M. Petroff, D. Gershoni, Appl. Phys. Lett. 74 (1999) 2194. [17] H. Htoon, J.W. Keto, O. Baklenov, A.L. Holmes Jr., C.K. Shin, Appl. Phys. Lett. 76 (2000) 700.