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InP double heterostructures grown by MOCVD
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Physica E 17 (2003) 229 – 231 www.elsevier.com/locate/physe
Optical study of direct interface in InP/InAlAs/InP double heterostructures grown by MOCVD J. Hellaraa , F. Hassena , H. Maaref a;∗ , V. Souliereb , Y. Monteilb a Laboratoire
de Physique des Semiconducteurs et des Composants Electroniques (LA-MA-06), Facult!e des Sciences de Monastir, Departement de Physique, Avenue de l’Environnement, 5000 Monastir, Tunisia b LMI-Universit! e Claude Bernard de Lyon-I, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France
Abstract A photoluminescence (PL) study of direct interface (InAlAs/InP) properties in InP/InAlAs heterostructures grown by metal–organic chemical vapor deposition on (1 0 0) InP substrate has been carried out. At low temperature, a broad PL band (FWHM = 120 meV) has been observed around 1 eV which is attributed to direct interface recombination. This PL line was strongly blue shifted (100 meV over three decades) when increasing the excitation density, and no saturation of the associated PL intensity was observed. This is the characteristic of type II or mixed type I–II transition. ? 2002 Published by Elsevier Science B.V. PACS: 78.20; 73.20; 78.66 Keywords: Optical properties; Interface; Photoluminescence; MOCVD
1. Introduction InAlAs/InP lattice-matched heterostructure is very attractive due to its type II band alignment which results in spatially indirect interband transitions across the interface [1–3]. Numerous studies have been published [1,4–6] claiming the observation of these type II transition in InAlAs/InP heterostructures in the 0.95 –1:3 m range, which becomes a promising candidate for the light source for optical ?ber communication. In this paper, we present the optical properties of an InP/InAlAs heterostructure grown on (1 0 0) InP substrates by low-pressure metal–organic chemical vapor deposition (MOCVD). Photoluminescence (PL)
∗
Corresponding author. Fax: +216-3-462-873. E-mail address: [email protected] (H. Maaref).
spectroscopy has been performed to study the properties of the direct interface InAlAs/InP. At low temperatures, the PL spectrum exhibits a broad PL band at 1 eV. This latter was found to be injection dependent which is a ?ngerprint of the type II transition. 2. Experiment The experiments are performed on a double heterostructure InP/InAlAs/InP labeled R2241. These samples have been grown at V=III = 50 by (MOCVD) on (1 0 0) InP substrates. A single heterostructure InAlAs/InP labeled R2330 was also used for comparison. Trimethylindium (TMIn), trimethylaluminium (TMAl), and arsine (AsH3 ) were the source materials. The InAlAs epilayer with a thickness of 300 nm is grown with a buFer layer of 150 nm. The InP cap
1386-9477/03/$ - see front matter ? 2002 Published by Elsevier Science B.V. doi:10.1016/S1386-9477(02)00770-1
230
J. Hellara et al. / Physica E 17 (2003) 229 – 231
(a) without cap layer
R2330 V/III=50
direct interface
PL intensity (a. u)
InP
(b) with cap layer
R2241 V/III=50
inverted interface
direct interface
SL
InP InAlAs 1.38 eV
(x5)
0.8
0.9
1.0
1
1.2
1.3
1.4
1.5
1.6
1.7
Energy (eV) Fig. 1. Low-temperature PL spectra of: (a) a single heterostructure InAlAs/InP(1 0 0) and (b) a double heterostructure InP/InAlAs/InP(1 0 0).
layer is typically 10 nm, the growth temperature is 600◦ C and the growth rate is about 0:17 nm=s.
3. Results and discussions In Fig. 1a the full PL spectrum of single heterostructure (InAlAs/InP) recorded at 10 K is shown. Two PL bands are observed. The intense one located at 0:95 eV is attributed to direct interface (InAlAs/InP). The second one situated at 1:42 eV is associated to the InP bulk material. In a double heterostructure sample, the PL spectrum (Fig. 1b) shows three additional peaks compared to that of a simple heterostructure. In our previous work, we have associated the peak located at 1:56 eV to the luminescence band of a natural superlattice (SL) induced by the presence of composition modulation in InAlAs epitaxial layer [7]. We have also demonstrated that this composition modulation is very sensitive to growth condition in particular to the V/III ratio and to the substrate orientation [7,8]. The peak located at 1:51 eV is attributed to InAlAs band gap. The PL peaks located at 1.42 and 1:38 eV are, respectively, the exciton peak and the electron
to acceptor (ebc –A0Zn ) recombination of the InP substrate [9,10]. Two other transitions appear at lower energies than that of InP bulk. The ?rst transition located at 1:25 eV, since it has never been observed in a single heterostructure (InAlAs/InP), is coupled to the inverted interface (InP/InAlAs). As previously mentioned [8], the latter was found to be injection and polarization dependent, the occurrence of spatially indirect transitions (type II) at InP/InAlAs interface was con?rmed by the optical data. A lowest PL band located at 1 eV which is observed in the reference sample (Fig. 1a) is attributed to the direct interface. This recombination is observed at lower energies, suggesting that a thin InAs quantum well (QW) is formed at the InAlAs/InP interface [2]. Simulation indicates that the presence of InAs extra layer is suitable to explain the 1 eV PL band. We note that the diFerent energy observed between the two samples correspond to the diFerence in the InAs layer thickness, resulting from the As–P exchange [11]. This process also aFects the optical and electrical properties of the InAlAs-based devices such as semiconductor lasers or transistors. In order to study the characteristics and the origin of this radiative transition, we have determined
J. Hellara et al. / Physica E 17 (2003) 229 – 231
231
1.06
Energy (eV)
1.02 1.00 100
0.98 0.96 0.94
Integrated PL intensity (a. u)
1000 1.04
0.92 10 0.1
1
10
Power (W/cm2) Fig. 2. Excitation density dependence of the energy (left scale) and of the integrated PL intensity (right scale) of the direct interface transition.
the dependence of the direct interface peak energy and peak intensity on the laser excitation power (Fig. 2). A strong blue shift is observed (100 meV over three decades). We attribute this latter to the type II transition in the InAlAs/InP interface. Most of the previous studies [12–14] did not mention any injection-dependent energy for direct InAlAs/InP heterostructures. The study of some groups [4,6,11] is the only exception, but the measured blue shift is very low. Furthermore, the integrated PL intensity of the 1 eV PL emission was found to be exponentially dependant on the density of excitation over three decades. No saturation took place in the range measured. This indicates that this PL transition is not attributed to any impurity or defects related but is an excitonic recombination. 4. Conclusion The direct interface (InAlAs/InP) has been characterized by PL. A broad PL emission observed at 1 eV is attributed to direct interface recombination. The latter is strongly blue shifted (100 meV over three decades) when the excitation intensity increased. This is characteristic of type II or mixed type I–II transition.
References [1] D. Vignaud, X. Wallart, F. Mollot, B. Sermage, J. Appl. Phys. 84 (1998) 2138. [2] V. Duez, O. VanbNesien, D. Lippens, D. Vignaud, X. Wallart, F. Mollot, J. Appl. Phys. 85 (1999) 2202. [3] E. Laugagne-Delpon, P. Voisin, J.P. Vieren, M. Voos, J.P. AndrNe, J.N. Patillon, Semicond. Sci. Technol. 7 (1992) 524. [4] D. Vignaud, X. Wallart, F. Mollot, J. Appl. Phys. 76 (1994) 2324. [5] L. Aina, M. Mattingly, L. Stecker, Appl. Phys. Lett. 53 (1988) 1620. [6] L.C. PoOcas, J.L. Duarte, I.F. Dias, E. Laureto, S.A. LourenOco, D.O.T. Flho, E.A. Meneses, I. Mazzaro, J.C. Harmand, J. Appl. Phys. 91 (2002) 8999. [7] K. Borgi, M. Hjiri, F. Hassen, H. Maaref, V. Souliere, Y. Monteil, Microelectron. Eng. 51–52 (2000) 299. [8] J. Hellara, K. Borgi, H. Maaref, V. Souliere, Y. Monteil, Mater. Sci. Eng. C 21 (2002) 231. [9] N. Pan, J. Carter, J. Elliott, H. Hendriks, S. Brierley, K.C. Hsieh, Appl. Phys. Lett. 63 (1993) 3029. [10] S.M. Olsthoorn, F.A.J.M. Driessen, J. Giling, J. Appl. Phys. 73 (1993) 7804. [11] J. BQohrer, A. Krost, R. Heitz, F. HeinrichsdorF, L. Eckey, D. Bimberg, H. Cerva, Appl. Phys. Lett. 68 (1996) 1072. [12] M. Kondow, S. Mingawa, Y. Inoue, T. Nishino, Y. Hamakawa, Appl. Phys. Lett. 54 (1989) 1760. [13] T. Yamamoto, M. Kasu, S. Noda, A. Sasok, J. Appl. Phys. 68 (1990) 5318. [14] W. Seidel, P. Voisin, J.P. AndrNe, F. Borgani, Solid State Electron. 40 (1996) 729.
Physica E 17 (2003) 229 – 231 www.elsevier.com/locate/physe
Optical study of direct interface in InP/InAlAs/InP double heterostructures grown by MOCVD J. Hellaraa , F. Hassena , H. Maaref a;∗ , V. Souliereb , Y. Monteilb a Laboratoire
de Physique des Semiconducteurs et des Composants Electroniques (LA-MA-06), Facult!e des Sciences de Monastir, Departement de Physique, Avenue de l’Environnement, 5000 Monastir, Tunisia b LMI-Universit! e Claude Bernard de Lyon-I, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France
Abstract A photoluminescence (PL) study of direct interface (InAlAs/InP) properties in InP/InAlAs heterostructures grown by metal–organic chemical vapor deposition on (1 0 0) InP substrate has been carried out. At low temperature, a broad PL band (FWHM = 120 meV) has been observed around 1 eV which is attributed to direct interface recombination. This PL line was strongly blue shifted (100 meV over three decades) when increasing the excitation density, and no saturation of the associated PL intensity was observed. This is the characteristic of type II or mixed type I–II transition. ? 2002 Published by Elsevier Science B.V. PACS: 78.20; 73.20; 78.66 Keywords: Optical properties; Interface; Photoluminescence; MOCVD
1. Introduction InAlAs/InP lattice-matched heterostructure is very attractive due to its type II band alignment which results in spatially indirect interband transitions across the interface [1–3]. Numerous studies have been published [1,4–6] claiming the observation of these type II transition in InAlAs/InP heterostructures in the 0.95 –1:3 m range, which becomes a promising candidate for the light source for optical ?ber communication. In this paper, we present the optical properties of an InP/InAlAs heterostructure grown on (1 0 0) InP substrates by low-pressure metal–organic chemical vapor deposition (MOCVD). Photoluminescence (PL)
∗
Corresponding author. Fax: +216-3-462-873. E-mail address: [email protected] (H. Maaref).
spectroscopy has been performed to study the properties of the direct interface InAlAs/InP. At low temperatures, the PL spectrum exhibits a broad PL band at 1 eV. This latter was found to be injection dependent which is a ?ngerprint of the type II transition. 2. Experiment The experiments are performed on a double heterostructure InP/InAlAs/InP labeled R2241. These samples have been grown at V=III = 50 by (MOCVD) on (1 0 0) InP substrates. A single heterostructure InAlAs/InP labeled R2330 was also used for comparison. Trimethylindium (TMIn), trimethylaluminium (TMAl), and arsine (AsH3 ) were the source materials. The InAlAs epilayer with a thickness of 300 nm is grown with a buFer layer of 150 nm. The InP cap
1386-9477/03/$ - see front matter ? 2002 Published by Elsevier Science B.V. doi:10.1016/S1386-9477(02)00770-1
230
J. Hellara et al. / Physica E 17 (2003) 229 – 231
(a) without cap layer
R2330 V/III=50
direct interface
PL intensity (a. u)
InP
(b) with cap layer
R2241 V/III=50
inverted interface
direct interface
SL
InP InAlAs 1.38 eV
(x5)
0.8
0.9
1.0
1
1.2
1.3
1.4
1.5
1.6
1.7
Energy (eV) Fig. 1. Low-temperature PL spectra of: (a) a single heterostructure InAlAs/InP(1 0 0) and (b) a double heterostructure InP/InAlAs/InP(1 0 0).
layer is typically 10 nm, the growth temperature is 600◦ C and the growth rate is about 0:17 nm=s.
3. Results and discussions In Fig. 1a the full PL spectrum of single heterostructure (InAlAs/InP) recorded at 10 K is shown. Two PL bands are observed. The intense one located at 0:95 eV is attributed to direct interface (InAlAs/InP). The second one situated at 1:42 eV is associated to the InP bulk material. In a double heterostructure sample, the PL spectrum (Fig. 1b) shows three additional peaks compared to that of a simple heterostructure. In our previous work, we have associated the peak located at 1:56 eV to the luminescence band of a natural superlattice (SL) induced by the presence of composition modulation in InAlAs epitaxial layer [7]. We have also demonstrated that this composition modulation is very sensitive to growth condition in particular to the V/III ratio and to the substrate orientation [7,8]. The peak located at 1:51 eV is attributed to InAlAs band gap. The PL peaks located at 1.42 and 1:38 eV are, respectively, the exciton peak and the electron
to acceptor (ebc –A0Zn ) recombination of the InP substrate [9,10]. Two other transitions appear at lower energies than that of InP bulk. The ?rst transition located at 1:25 eV, since it has never been observed in a single heterostructure (InAlAs/InP), is coupled to the inverted interface (InP/InAlAs). As previously mentioned [8], the latter was found to be injection and polarization dependent, the occurrence of spatially indirect transitions (type II) at InP/InAlAs interface was con?rmed by the optical data. A lowest PL band located at 1 eV which is observed in the reference sample (Fig. 1a) is attributed to the direct interface. This recombination is observed at lower energies, suggesting that a thin InAs quantum well (QW) is formed at the InAlAs/InP interface [2]. Simulation indicates that the presence of InAs extra layer is suitable to explain the 1 eV PL band. We note that the diFerent energy observed between the two samples correspond to the diFerence in the InAs layer thickness, resulting from the As–P exchange [11]. This process also aFects the optical and electrical properties of the InAlAs-based devices such as semiconductor lasers or transistors. In order to study the characteristics and the origin of this radiative transition, we have determined
J. Hellara et al. / Physica E 17 (2003) 229 – 231
231
1.06
Energy (eV)
1.02 1.00 100
0.98 0.96 0.94
Integrated PL intensity (a. u)
1000 1.04
0.92 10 0.1
1
10
Power (W/cm2) Fig. 2. Excitation density dependence of the energy (left scale) and of the integrated PL intensity (right scale) of the direct interface transition.
the dependence of the direct interface peak energy and peak intensity on the laser excitation power (Fig. 2). A strong blue shift is observed (100 meV over three decades). We attribute this latter to the type II transition in the InAlAs/InP interface. Most of the previous studies [12–14] did not mention any injection-dependent energy for direct InAlAs/InP heterostructures. The study of some groups [4,6,11] is the only exception, but the measured blue shift is very low. Furthermore, the integrated PL intensity of the 1 eV PL emission was found to be exponentially dependant on the density of excitation over three decades. No saturation took place in the range measured. This indicates that this PL transition is not attributed to any impurity or defects related but is an excitonic recombination. 4. Conclusion The direct interface (InAlAs/InP) has been characterized by PL. A broad PL emission observed at 1 eV is attributed to direct interface recombination. The latter is strongly blue shifted (100 meV over three decades) when the excitation intensity increased. This is characteristic of type II or mixed type I–II transition.
References [1] D. Vignaud, X. Wallart, F. Mollot, B. Sermage, J. Appl. Phys. 84 (1998) 2138. [2] V. Duez, O. VanbNesien, D. Lippens, D. Vignaud, X. Wallart, F. Mollot, J. Appl. Phys. 85 (1999) 2202. [3] E. Laugagne-Delpon, P. Voisin, J.P. Vieren, M. Voos, J.P. AndrNe, J.N. Patillon, Semicond. Sci. Technol. 7 (1992) 524. [4] D. Vignaud, X. Wallart, F. Mollot, J. Appl. Phys. 76 (1994) 2324. [5] L. Aina, M. Mattingly, L. Stecker, Appl. Phys. Lett. 53 (1988) 1620. [6] L.C. PoOcas, J.L. Duarte, I.F. Dias, E. Laureto, S.A. LourenOco, D.O.T. Flho, E.A. Meneses, I. Mazzaro, J.C. Harmand, J. Appl. Phys. 91 (2002) 8999. [7] K. Borgi, M. Hjiri, F. Hassen, H. Maaref, V. Souliere, Y. Monteil, Microelectron. Eng. 51–52 (2000) 299. [8] J. Hellara, K. Borgi, H. Maaref, V. Souliere, Y. Monteil, Mater. Sci. Eng. C 21 (2002) 231. [9] N. Pan, J. Carter, J. Elliott, H. Hendriks, S. Brierley, K.C. Hsieh, Appl. Phys. Lett. 63 (1993) 3029. [10] S.M. Olsthoorn, F.A.J.M. Driessen, J. Giling, J. Appl. Phys. 73 (1993) 7804. [11] J. BQohrer, A. Krost, R. Heitz, F. HeinrichsdorF, L. Eckey, D. Bimberg, H. Cerva, Appl. Phys. Lett. 68 (1996) 1072. [12] M. Kondow, S. Mingawa, Y. Inoue, T. Nishino, Y. Hamakawa, Appl. Phys. Lett. 54 (1989) 1760. [13] T. Yamamoto, M. Kasu, S. Noda, A. Sasok, J. Appl. Phys. 68 (1990) 5318. [14] W. Seidel, P. Voisin, J.P. AndrNe, F. Borgani, Solid State Electron. 40 (1996) 729.