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Photoluminescence excitation spectroscopy of erbium in epitaxially grown Si:Er structures
Optical Materials 27 (2005) 890–893 www.elsevier.com/locate/optmat
Photoluminescence excitation spectroscopy of erbium in epitaxially grown Si:Er structures A.N. Yablonskiy
a,*
, M.A.J. Klik b, B.A. Andreev a, V.P. Kuznetsov c, Z.F. Krasilnik a, T. Gregorkiewicz b
a
c
Institute for Physics of Microstructures, Russian Academy of Sciences, GSP-105, 603950 Nizhny Novgorod, Russia b Van der Waals-Zeeman Institute, University of Amsterdam, NL-1018 XE Amsterdam, The Netherlands Physical Technical Research Institute, University of Nizhny Novgorod, 23 Gagarin Ave., 603950 Nizhny Novgorod, Russia Available online 18 October 2004
Abstract Excitation of erbium photoluminescence in Si:Er epitaxial structures has been studied within a broad pump wavelength range (kex = 780–1500 nm). In all the investigated structures considerable signal of the 1.5 lm erbium photoluminescence has been observed at pump photon energies well below the silicon band-gap value (kex > 1060 nm) where seemingly no exciton generation occurs. Possible mechanism of erbium ion excitation in silicon without participation of excitons is discussed. 2004 Elsevier B.V. All rights reserved.
1. Introduction Erbium-doped silicon has become a subject of considerable interest because the wavelength of its radiative transition 4I13/2 ! 4I15/2 in the 4f-shell of the Er3+ ion (k = 1.54 lm) lies in the spectral region of maximum transparency and minimum dispersion of quartz optical-fiber communication lines. Application of sublimation molecular-beam epitaxy (SMBE) [1] makes it possible to produce uniformly and selectively doped Si:Er structures with high crystalline quality which exhibit strong erbium photo- and electro-luminescence at 1.54 lm [2]. Excitation of erbium ions in silicon via electronic states of the host is known to be much more efficient than by direct optical pumping of the 4-f electron shell [3,4]. At the same time, it is universally accepted that such an indirect energy transfer is a complex multistage process involving impurity levels in the silicon band gap. *
Corresponding author. Tel.: +7 8312 675037x256; fax: +7 8312 609111. E-mail address: [email protected] (A.N. Yablonskiy). 0925-3467/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2004.08.030
In spite of much investigation, details of this excitation mechanism remain poorly understood. This motivated the present study of the excitation of erbium photoluminescence (PL) for various values of the pump photon energy in SMBE-grown Si:Er structures containing a variety of optically active erbium centers.
2. Experimental Erbium-doped silicon structures were SMBE grown on p-type [1 0 0]-oriented Si substrates with an electrical resistivity q 10–20 X cm with the use of a Si:Er crystal source. The thickness of the studied epitaxial structures varied from 1.8 to 5.5 lm. The growth temperature was varied from 500 to 600 C. Details on the preparation of the Si:Er samples by SMBE method are reported in Refs. [5,6]. According to SIMS measurements, the structures contain 5 · 1018 cm3 of Er atoms, 5 · 1019 cm3 of O atoms, and from 4 · 1018 to 1 · 1019 cm3 of C atoms. A near-IR investigation of erbium PL excitation spectra in the Si:Er/Si structures (kex = 780–1500 nm) was made with an optical parametric oscillator pumped by
A.N. Yablonskiy et al. / Optical Materials 27 (2005) 890–893
0.8
Si band gap p = 1.00 p = 0.55 p = 0.24 p = 0.10 p = 0.03 p = 0.004
0.7
Erbium PL intensity, a.u.
a pulsed Nd:YAG laser (355 nm). The pump pulse duration was 5 ns, the pulse repetition frequency was 20 Hz, and the maximum pulse energy was 7 mJ at a wavelength of 780 nm. Thus, the maximum pulse power was as high as 106 W. The PL signal was measured with a grating spectrometer, a germanium detector, and a digital oscilloscope (TDS 3032 Tektronix). The excitation spectra of the 1.5 lm erbium PL were recorded at 10 K using a closed-cycle cryostat (Oxford Instruments).
891
0.6 0.5 0.4 0.3
p= P / P max, Pmax ~ 10 6 W
0.2 0.1
3. Results and discussion
0.0
Excitation spectra of erbium PL were measured for a series of SMBE grown Si:Er structures in the broad range of excitation wavelengths (kex = 780–1500 nm). For PLE measurements, the spectrometer was set to the maximum of the erbium luminescence signal at k = 1537 nm see Fig. 1. As can be seen, in addition to the band-to-band excitation, considerable signal of Er PL can be observed also upon illumination with photons whose energies are significantly smaller than the band gap of silicon (kex > 1060 nm) (see Fig. 2). Moreover, at high pumping power a rapid increase of the Er PL intensity with excitation wavelength was observed in the range 1000–1050 nm, which corresponds to the edge of light absorption in bulk silicon. Fig. 1 displays PL spectra for the pump photon energies above (kex = 980 nm), near (kex = 1040 nm) and below (kex = 1100 nm) the band gap of Si obtained at the maximum pump power (P = 106 W). The obtained PL spectra are typical for erbium in structures with SiO2-like precipitates. This provides further support to the fact that the PL signal observed for kex > 1060 nm (i.e., for hmex < Eg) originates also from Er3+ ions. In accordance with the generally accepted models, the interband pumping (with photon energy above the sili-
PL intensity, a.u.
λ ex = 1030 nm
0.2
1540
1545
1550
1555
1400
1500
Si band gap
0.6
0.4
Erbium PL Exciton PL
0.2
0.1
1535
1300
0.8
λ ex = 1100 nm
1530
1200
1.0
0.3
0.0 1525
1100
con band gap) is necessary for excitation of erbium PL in silicon. It results in the generation of electron–hole pairs, subsequent formation of excitons, localization of the excitons at the erbium-related centers, and, finally, nonradiative recombination of the bound excitons with energy transfer to the erbium ions [7]. In order to gain more information on the mechanism of sub-band-gap excitation of erbium PL, and, in particular, to establish its relation with excitons, we also measured PLE of the exciton band in the same sample. In this case, the luminescence signal originates mostly from the radiative recombination of the excitons bound at the shallow impurity levels in the substrate of the Si:Er/Si structures. As can be seen from the Fig. 3, strong decrease of exciton PL intensity takes place in the wavelength range kex = 1000–1050 nm. As could be expected, no noticeable signal of the band-to-band PL was observed at excitation photon energies below the Si band-gap
λ ex = 980 nm
0.4
1000
Fig. 2. Erbium PL excitation spectra (kPL = 1540 nm) of SMBE Si:Er structure obtained at various pump power levels.
spectrometer position during the PLE measurements
0.5
900
Excitation wavelength, nm
PL Intensity, a.u.
0.6
800
1560
Wavelength, cm-1 Fig. 1. Erbium PL spectra measured at different excitation wavelengths kex.
0.0 800
850
900
950
1000
1050
1100
1150
1200
Excitation wavelength, nm Fig. 3. Comparison of PLE spectra of erbium- and exciton-related emissions.
892
A.N. Yablonskiy et al. / Optical Materials 27 (2005) 890–893
(kex > 1060 nm). This drop in the exciton PL intensity is associated with a decrease in the absorption coefficient of silicon in the wavelength region in question and, as a consequence, a decrease in the intensity of electron– hole pair generation. On the other hand, this result indicates that, under conditions of sub-band-gap pumping, the excitation of the erbium ions must proceed without participation of excitons. It should be pointed out that at kex > 1060 nm the samples become almost optically transparent for the incoming radiation. Since under these conditions only a small part of the pump power is absorbed in the sample, this feature implies that the specific excitation mechanism active in this spectral region (kex > 1060 nm) must be particularly efficient. As can be seen from Fig. 2, the effect of sub-band-gap excitation of erbium PL and the characteristic peak in the PLE spectra at kex = 1040 nm are more pronounced at high pumping powers. This can be explained by comparing the power dependence of the Er PL intensity for the excitation above (kex < 1060 nm) and below (kex > 1060 nm) the band gap of silicon, as shown in Fig. 4. The PL signal under the above-band-gap excitation is almost saturated at the highest power, whereas for a below-band-gap excitation the power dependence is almost linear. This can also explain the fact that no below-band-gap excitation has been observed in the previous studies—see, e.g. Ref. [8]—when continuous-wave pumping with much lower power density was used. From the obtained experimental data, and, in particular, from the high efficiency of Er PL, we can conclude that for hmex < Eg the absorption occurs in the epitaxial erbium-doped layers. The observation of sub-band-gap excitation of erbium PL can be explained with the assumption of Er-related impurity levels in the silicon band gap are formed in the epitaxial layers. Indeed,
erbium-doped silicon layers are known to show, as a rule, an n-type conductivity. In such a case, the absorption of a photon of energy hmex < Eg could promote electrons from the valence band directly to the donor levels associated with erbium. Subsequent nonradiative recombination of these electrons with holes in the valence band could deliver the energy necessary for the excitation of Er ions. The proposed mechanism is schematically depicted on the Fig. 5. The proposed mechanism of erbium ion excitation can also account for the increase in the erbium PL intensity at longer excitation wavelengths, as experimentally observed in the range kex = 1000–1030 nm. The bandto-band pumping of Si:Er structures generates a large number of electron–hole pairs, which gives rise to the onset of intense, free-carrier-mediated nonradiative Auger-deexcitation of Er ions, thus substantially lowering the efficiency of erbium PL. As the pump photon energy decreases, the light absorption coefficient in bulk silicon drops sharply in the vicinity of Eg, which leads to a sharp drop in the number of free carriers created in the structure. Therefore, the Auger deexcitation efficiency decreases strongly, thereby increasing the erbium PL signal.
4. Conclusions
1.6
λex = 940 nm
1.4
λex = 1040 nm
1.2
PL Intensity, a.u.
Fig. 5. A possible schematic mechanism of sub-band-gap excitation (hmex < Eg) of erbium in silicon.
λex = 1100 nm
1.0 0.8 0.6 0.4 0.2 0.0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Pumping power, P / Pmax Fig. 4. Power dependence of erbium PL intensity for the excitation photon energy above (kex = 940 nm), near (kex = 1040 nm) and below (kex = 1100 nm) the band gap energy of silicon.
The excitation spectra of Er photoluminescence in SMBE-grown Si:Er structures have been measured using Nd: YAG-pumped optical parametric oscillator in the wide range of the excitation wavelength (kex = 780– 1500 nm). It has been shown that a considerable signal of erbium PL can be obtained with excitation photon energies much lower than the band gap of Si (kex > 1060 nm). Moreover, at high pumping power rapid increase of the Er luminescence intensity has been observed in the range 1000–1030 nm of the excitation wavelength. At the same time no noticeable signal was observed for the band-to-band luminescence at excitation photon energies below the Si band-gap (kex > 1060 nm). This indicates that, under conditions of sub-band-gap pumping, the excitation of the erbium ions proceeds without participation of excitons. We postulate that the sub-band-gap excitation of erbium ions is
A.N. Yablonskiy et al. / Optical Materials 27 (2005) 890–893
mediated by the Er-induced defect levels in the epitaxial Si:Er layers. Suppression of nonradiative Auger deexcitation of Er ions is proposed to explain the high efficiency of erbium PL sub-band-gap excitation.
[2]
Acknowledgements
[3]
This work was supported by NWO 047-009-013, INTAS 01-0194, 01-0468, 03-51-6486, RFBR 02-02-16773.
[4] [5] [6]
References [1] B.A. Andreev, A.Yu. Andreev, H. Ellmer, H. Hutter, Z.F. Krasilnik, V.P. Kuznetsov, S. Lanzerstorfer, L. Palmetshofer, K.
[7] [8]
893
Piplits, R.A. Rubtsova, N.S. Sokolov, V.B. Shmagin, M.V. Stepikhova, E.A. Uskova, J. Cryst. Growth 201&202 (1999) 534. Z.F. Krasilnik, V.Ya. Aleshkin, B.A. Andreev, O.B. Gusev, W. Jantsch, L.V. Krasilnikova, D.I. Kryzhkov, V.P. Kuznetsov, V.G. Shengurov, V.B. Shmagin, N.A. Sobolev, M.V. Stepikhova, A.N. Yablonsky, in: L. Pavesi et al. (Eds.), Towards the First Silicon Laser, Kluwer Academic Publishers, The Netherlands, 2003, p. 445. F. Priolo, G. Franzo, S. Coffa, A. Carnera, Phys. Rev. B 57 (8) (1998) 4443. O.B. Gusev, M.S. Bresler, P.E. Pak, I.N. Yassievich, M. Forcales, N.Q. Vinh, T. Gregorkiewicz, Phys. Rev. B 64 (2001) 075302. V.P. Kuznetsov, R.A. Rubtsova, Semiconductors 34 (5) (2000) 502. B. Andreev, V. Chalkov, O. Gusev, A. EmelÕyanov, Z. KrasilÕnik, V. Kuznetsov, P. Pak, V. Shabanov, V. Shengurov, V. Shmagin, N. Sobolev, M. Stepikhova, S. Svetlov, Nanotechnology 13 (2002) 97. M.S. Bresler et al., Phys. Solid State 38 (5) (1996) 813. W.L. Ng, M.P. Temple, P.A. Childs, F. Wellhofer, K.P. Homewood, Appl. Phys. Lett. 75 (1) (1999) 97.
Photoluminescence excitation spectroscopy of erbium in epitaxially grown Si:Er structures A.N. Yablonskiy
a,*
, M.A.J. Klik b, B.A. Andreev a, V.P. Kuznetsov c, Z.F. Krasilnik a, T. Gregorkiewicz b
a
c
Institute for Physics of Microstructures, Russian Academy of Sciences, GSP-105, 603950 Nizhny Novgorod, Russia b Van der Waals-Zeeman Institute, University of Amsterdam, NL-1018 XE Amsterdam, The Netherlands Physical Technical Research Institute, University of Nizhny Novgorod, 23 Gagarin Ave., 603950 Nizhny Novgorod, Russia Available online 18 October 2004
Abstract Excitation of erbium photoluminescence in Si:Er epitaxial structures has been studied within a broad pump wavelength range (kex = 780–1500 nm). In all the investigated structures considerable signal of the 1.5 lm erbium photoluminescence has been observed at pump photon energies well below the silicon band-gap value (kex > 1060 nm) where seemingly no exciton generation occurs. Possible mechanism of erbium ion excitation in silicon without participation of excitons is discussed. 2004 Elsevier B.V. All rights reserved.
1. Introduction Erbium-doped silicon has become a subject of considerable interest because the wavelength of its radiative transition 4I13/2 ! 4I15/2 in the 4f-shell of the Er3+ ion (k = 1.54 lm) lies in the spectral region of maximum transparency and minimum dispersion of quartz optical-fiber communication lines. Application of sublimation molecular-beam epitaxy (SMBE) [1] makes it possible to produce uniformly and selectively doped Si:Er structures with high crystalline quality which exhibit strong erbium photo- and electro-luminescence at 1.54 lm [2]. Excitation of erbium ions in silicon via electronic states of the host is known to be much more efficient than by direct optical pumping of the 4-f electron shell [3,4]. At the same time, it is universally accepted that such an indirect energy transfer is a complex multistage process involving impurity levels in the silicon band gap. *
Corresponding author. Tel.: +7 8312 675037x256; fax: +7 8312 609111. E-mail address: [email protected] (A.N. Yablonskiy). 0925-3467/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2004.08.030
In spite of much investigation, details of this excitation mechanism remain poorly understood. This motivated the present study of the excitation of erbium photoluminescence (PL) for various values of the pump photon energy in SMBE-grown Si:Er structures containing a variety of optically active erbium centers.
2. Experimental Erbium-doped silicon structures were SMBE grown on p-type [1 0 0]-oriented Si substrates with an electrical resistivity q 10–20 X cm with the use of a Si:Er crystal source. The thickness of the studied epitaxial structures varied from 1.8 to 5.5 lm. The growth temperature was varied from 500 to 600 C. Details on the preparation of the Si:Er samples by SMBE method are reported in Refs. [5,6]. According to SIMS measurements, the structures contain 5 · 1018 cm3 of Er atoms, 5 · 1019 cm3 of O atoms, and from 4 · 1018 to 1 · 1019 cm3 of C atoms. A near-IR investigation of erbium PL excitation spectra in the Si:Er/Si structures (kex = 780–1500 nm) was made with an optical parametric oscillator pumped by
A.N. Yablonskiy et al. / Optical Materials 27 (2005) 890–893
0.8
Si band gap p = 1.00 p = 0.55 p = 0.24 p = 0.10 p = 0.03 p = 0.004
0.7
Erbium PL intensity, a.u.
a pulsed Nd:YAG laser (355 nm). The pump pulse duration was 5 ns, the pulse repetition frequency was 20 Hz, and the maximum pulse energy was 7 mJ at a wavelength of 780 nm. Thus, the maximum pulse power was as high as 106 W. The PL signal was measured with a grating spectrometer, a germanium detector, and a digital oscilloscope (TDS 3032 Tektronix). The excitation spectra of the 1.5 lm erbium PL were recorded at 10 K using a closed-cycle cryostat (Oxford Instruments).
891
0.6 0.5 0.4 0.3
p= P / P max, Pmax ~ 10 6 W
0.2 0.1
3. Results and discussion
0.0
Excitation spectra of erbium PL were measured for a series of SMBE grown Si:Er structures in the broad range of excitation wavelengths (kex = 780–1500 nm). For PLE measurements, the spectrometer was set to the maximum of the erbium luminescence signal at k = 1537 nm see Fig. 1. As can be seen, in addition to the band-to-band excitation, considerable signal of Er PL can be observed also upon illumination with photons whose energies are significantly smaller than the band gap of silicon (kex > 1060 nm) (see Fig. 2). Moreover, at high pumping power a rapid increase of the Er PL intensity with excitation wavelength was observed in the range 1000–1050 nm, which corresponds to the edge of light absorption in bulk silicon. Fig. 1 displays PL spectra for the pump photon energies above (kex = 980 nm), near (kex = 1040 nm) and below (kex = 1100 nm) the band gap of Si obtained at the maximum pump power (P = 106 W). The obtained PL spectra are typical for erbium in structures with SiO2-like precipitates. This provides further support to the fact that the PL signal observed for kex > 1060 nm (i.e., for hmex < Eg) originates also from Er3+ ions. In accordance with the generally accepted models, the interband pumping (with photon energy above the sili-
PL intensity, a.u.
λ ex = 1030 nm
0.2
1540
1545
1550
1555
1400
1500
Si band gap
0.6
0.4
Erbium PL Exciton PL
0.2
0.1
1535
1300
0.8
λ ex = 1100 nm
1530
1200
1.0
0.3
0.0 1525
1100
con band gap) is necessary for excitation of erbium PL in silicon. It results in the generation of electron–hole pairs, subsequent formation of excitons, localization of the excitons at the erbium-related centers, and, finally, nonradiative recombination of the bound excitons with energy transfer to the erbium ions [7]. In order to gain more information on the mechanism of sub-band-gap excitation of erbium PL, and, in particular, to establish its relation with excitons, we also measured PLE of the exciton band in the same sample. In this case, the luminescence signal originates mostly from the radiative recombination of the excitons bound at the shallow impurity levels in the substrate of the Si:Er/Si structures. As can be seen from the Fig. 3, strong decrease of exciton PL intensity takes place in the wavelength range kex = 1000–1050 nm. As could be expected, no noticeable signal of the band-to-band PL was observed at excitation photon energies below the Si band-gap
λ ex = 980 nm
0.4
1000
Fig. 2. Erbium PL excitation spectra (kPL = 1540 nm) of SMBE Si:Er structure obtained at various pump power levels.
spectrometer position during the PLE measurements
0.5
900
Excitation wavelength, nm
PL Intensity, a.u.
0.6
800
1560
Wavelength, cm-1 Fig. 1. Erbium PL spectra measured at different excitation wavelengths kex.
0.0 800
850
900
950
1000
1050
1100
1150
1200
Excitation wavelength, nm Fig. 3. Comparison of PLE spectra of erbium- and exciton-related emissions.
892
A.N. Yablonskiy et al. / Optical Materials 27 (2005) 890–893
(kex > 1060 nm). This drop in the exciton PL intensity is associated with a decrease in the absorption coefficient of silicon in the wavelength region in question and, as a consequence, a decrease in the intensity of electron– hole pair generation. On the other hand, this result indicates that, under conditions of sub-band-gap pumping, the excitation of the erbium ions must proceed without participation of excitons. It should be pointed out that at kex > 1060 nm the samples become almost optically transparent for the incoming radiation. Since under these conditions only a small part of the pump power is absorbed in the sample, this feature implies that the specific excitation mechanism active in this spectral region (kex > 1060 nm) must be particularly efficient. As can be seen from Fig. 2, the effect of sub-band-gap excitation of erbium PL and the characteristic peak in the PLE spectra at kex = 1040 nm are more pronounced at high pumping powers. This can be explained by comparing the power dependence of the Er PL intensity for the excitation above (kex < 1060 nm) and below (kex > 1060 nm) the band gap of silicon, as shown in Fig. 4. The PL signal under the above-band-gap excitation is almost saturated at the highest power, whereas for a below-band-gap excitation the power dependence is almost linear. This can also explain the fact that no below-band-gap excitation has been observed in the previous studies—see, e.g. Ref. [8]—when continuous-wave pumping with much lower power density was used. From the obtained experimental data, and, in particular, from the high efficiency of Er PL, we can conclude that for hmex < Eg the absorption occurs in the epitaxial erbium-doped layers. The observation of sub-band-gap excitation of erbium PL can be explained with the assumption of Er-related impurity levels in the silicon band gap are formed in the epitaxial layers. Indeed,
erbium-doped silicon layers are known to show, as a rule, an n-type conductivity. In such a case, the absorption of a photon of energy hmex < Eg could promote electrons from the valence band directly to the donor levels associated with erbium. Subsequent nonradiative recombination of these electrons with holes in the valence band could deliver the energy necessary for the excitation of Er ions. The proposed mechanism is schematically depicted on the Fig. 5. The proposed mechanism of erbium ion excitation can also account for the increase in the erbium PL intensity at longer excitation wavelengths, as experimentally observed in the range kex = 1000–1030 nm. The bandto-band pumping of Si:Er structures generates a large number of electron–hole pairs, which gives rise to the onset of intense, free-carrier-mediated nonradiative Auger-deexcitation of Er ions, thus substantially lowering the efficiency of erbium PL. As the pump photon energy decreases, the light absorption coefficient in bulk silicon drops sharply in the vicinity of Eg, which leads to a sharp drop in the number of free carriers created in the structure. Therefore, the Auger deexcitation efficiency decreases strongly, thereby increasing the erbium PL signal.
4. Conclusions
1.6
λex = 940 nm
1.4
λex = 1040 nm
1.2
PL Intensity, a.u.
Fig. 5. A possible schematic mechanism of sub-band-gap excitation (hmex < Eg) of erbium in silicon.
λex = 1100 nm
1.0 0.8 0.6 0.4 0.2 0.0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Pumping power, P / Pmax Fig. 4. Power dependence of erbium PL intensity for the excitation photon energy above (kex = 940 nm), near (kex = 1040 nm) and below (kex = 1100 nm) the band gap energy of silicon.
The excitation spectra of Er photoluminescence in SMBE-grown Si:Er structures have been measured using Nd: YAG-pumped optical parametric oscillator in the wide range of the excitation wavelength (kex = 780– 1500 nm). It has been shown that a considerable signal of erbium PL can be obtained with excitation photon energies much lower than the band gap of Si (kex > 1060 nm). Moreover, at high pumping power rapid increase of the Er luminescence intensity has been observed in the range 1000–1030 nm of the excitation wavelength. At the same time no noticeable signal was observed for the band-to-band luminescence at excitation photon energies below the Si band-gap (kex > 1060 nm). This indicates that, under conditions of sub-band-gap pumping, the excitation of the erbium ions proceeds without participation of excitons. We postulate that the sub-band-gap excitation of erbium ions is
A.N. Yablonskiy et al. / Optical Materials 27 (2005) 890–893
mediated by the Er-induced defect levels in the epitaxial Si:Er layers. Suppression of nonradiative Auger deexcitation of Er ions is proposed to explain the high efficiency of erbium PL sub-band-gap excitation.
[2]
Acknowledgements
[3]
This work was supported by NWO 047-009-013, INTAS 01-0194, 01-0468, 03-51-6486, RFBR 02-02-16773.
[4] [5] [6]
References [1] B.A. Andreev, A.Yu. Andreev, H. Ellmer, H. Hutter, Z.F. Krasilnik, V.P. Kuznetsov, S. Lanzerstorfer, L. Palmetshofer, K.
[7] [8]
893
Piplits, R.A. Rubtsova, N.S. Sokolov, V.B. Shmagin, M.V. Stepikhova, E.A. Uskova, J. Cryst. Growth 201&202 (1999) 534. Z.F. Krasilnik, V.Ya. Aleshkin, B.A. Andreev, O.B. Gusev, W. Jantsch, L.V. Krasilnikova, D.I. Kryzhkov, V.P. Kuznetsov, V.G. Shengurov, V.B. Shmagin, N.A. Sobolev, M.V. Stepikhova, A.N. Yablonsky, in: L. Pavesi et al. (Eds.), Towards the First Silicon Laser, Kluwer Academic Publishers, The Netherlands, 2003, p. 445. F. Priolo, G. Franzo, S. Coffa, A. Carnera, Phys. Rev. B 57 (8) (1998) 4443. O.B. Gusev, M.S. Bresler, P.E. Pak, I.N. Yassievich, M. Forcales, N.Q. Vinh, T. Gregorkiewicz, Phys. Rev. B 64 (2001) 075302. V.P. Kuznetsov, R.A. Rubtsova, Semiconductors 34 (5) (2000) 502. B. Andreev, V. Chalkov, O. Gusev, A. EmelÕyanov, Z. KrasilÕnik, V. Kuznetsov, P. Pak, V. Shabanov, V. Shengurov, V. Shmagin, N. Sobolev, M. Stepikhova, S. Svetlov, Nanotechnology 13 (2002) 97. M.S. Bresler et al., Phys. Solid State 38 (5) (1996) 813. W.L. Ng, M.P. Temple, P.A. Childs, F. Wellhofer, K.P. Homewood, Appl. Phys. Lett. 75 (1) (1999) 97.