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On the optical properties of amorphous Ge–Ga–Se films prepared by pulsed laser deposition
Journal of Non-Crystalline Solids 326&327 (2003) 53–57 www.elsevier.com/locate/jnoncrysol
On the optical properties of amorphous Ge–Ga–Se films prepared by pulsed laser deposition P. Nemec
a,*
, J. Jedelsk y a, M. Frumar a, M. Munzar b, M. Jelınek c, J. Lancok
c
a
b
Department of General and Inorganic Chemistry and Research Center, University of Pardubice, Legions Sq. 565, 53210 Pardubice, Czech Republic Joint Laboratory of Solid State Chemistry of the Acad. Sci. of the Czech Republic and the University of Pardubice, 532 10 Pardubice, Czech Republic c Institute of Physics of Acad. Sci. of the Czech Republic, Na Slovance 2, 18221 Prague, Czech Republic
Abstract Amorphous Ge–Ga–Se thin films (pure and dysprosium doped) were prepared by the pulsed laser deposition technique using different energy of the laser beam pulses. The effects of exposure and thermal annealing below the glass transition temperature on the optical parameters (index of refraction, optical band gap) and the thickness of asdeposited chalcogenide thin films were studied. The optical band gap and the thickness of the thin films increased with exposure of the films and even more with the annealing. Index of refraction has an opposite tendency. Two emission bands with maxima near 1140 and 1340 nm corresponding to 6 F9=2 , 6 H7=2 –6 H15=2 and 6 F11=2 , 6 H9=2 –6 H15=2 electron transitions of Dy3þ ions were identified in luminescence spectra of dysprosium doped thin films. Ó 2003 Elsevier B.V. All rights reserved. PACS: 78.20.Ci; 78.30.Hv; 78.40.Ha; 78.66.Jg; 81.15.Fg
1. Introduction Study of thin amorphous multicomponent chalcogenide films is of large interest, because of fundamental science reasons and also due to potential applications of such films in integrated planar optical circuits and their components for routing, amplifying or generating of optical signal (mainly in infrared spectral region), as well as in diffractive optics, in holography, for photo-resists
*
Corresponding author. Tel.: +420-466 037 265; fax: +420466 037 144. E-mail address: [email protected] (P. Nemec).
and optical memories production and for other optoelectronic applications [1,2]. There are several advantages of using pulsed laser deposition (PLD) (known also as laser ablation) for thin films preparation with respect to classical techniques: (i) chemical composition of the deposited film is mostly close to used targets; (ii) the possibility of deposition of multicomponent thin films without large changes of composition; (iii) short process time; and (iv) the control of PLD process by the laser parameters [1–3]. The main present disadvantages of the PLD are: (i) the difficulty in preparing films of larger areas, of even surface, and of equal thickness; (ii) the presence of droplets in the deposited films [1–3]; and (iii) more expensive
0022-3093/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0022-3093(03)00376-4
54
P. Nemec et al. / Journal of Non-Crystalline Solids 326&327 (2003) 53–57
facility. In this work, results of a study of the optical properties, and their photo- and thermallyinduced changes of thin films from the Ge–Ga–Se system prepared by PLD are presented; photoluminescence spectrum of Dy doped Ge–Ga–Se thin films is given and interpreted.
2. Experimental Amorphous germanium–gallium–selenide thin films were prepared by PLD using rotating targets of chalcogenide glasses with nominal composition of Ge30 Ga5 Se65 and (Ge30 Ga5 Se65 )99:5 (Dy2 Se3 )0:5 , respectively. The target glasses were prepared by conventional melt-quenching according to our previous report [4]. KrF excimer laser (Lumonics PM 840) operating at 248 nm with constant output energy of 500 mJ per pulse and with a repetition rate of 10 Hz was used for preparation of thin films. An optical attenuator varied the energy density of the laser beam on the target from 1 to 5 J cm2 . Amorphous thin films were deposited in a vacuum chamber (background pressure <102 Pa). The substrates used for PLD (chemically cleaned microscope glass slides) were positioned parallel to the target surface at a distance of 5 cm. All the films were deposited at room temperature. The chemical composition of the films was checked using wavelength dispersive X-ray analyzer (WDX), in particular an electron superprobe Jeol JXA 733 with a microanalyzer Kevex D. The room-temperature optical transmissivity spectra of the thin chalcogenide films were measured using the spectrophotometers Perkin–Elmer Lambda 9 (400–1100 nm) and Bio-Rad FTS 175C (1000–2700 nm). In order to determine photo-induced changes of optical parameters, prepared films (as-deposited) were exposed by high-pressure mercury lamp (200 W, 1 h) in an inert atmosphere of pure Ar. In order to evaluate thermally-induced changes of the optical properties, exposed films were annealed at 300 °C for 1 h in pure Ar. Photo-luminescence spectra of dysprosium doped Ge–Ga–Se thin films in near infrared spectral region (1080–1600 nm) were measured using
CW pump laser operating at 1064 nm (Nd:YAG) and liquid nitrogen cooled Ge detector. 3. Results Prepared films were homogeneous, of dark red color, with smooth surface as results from the from surface profile measurements. The chemical composition of the thin films was found to be close to the composition of used targets in analogy with our previous paper [2]. In the films prepared from dysprosium containing targets was identified also Dy; its content was measured only qualitatively. Spectral dependencies of the refractive index were calculated from the optical transmission spectra of as-deposited, exposed and annealed thin films using the Swanepoel method [5], examples (for three different energies of the laser beam used for PLD) are given in Fig. 1. The error in determination of index of refraction is evaluated as ±0.015. The index of refraction increases with increasing energy of the laser beam used for PLD (Fig. 1). Exposure of the as-deposited films caused the decrease of the values of indices of refraction (Dnmax ¼ 0:11). After annealing of exposed films, values of index of refraction were further decreased (Dnmax ¼ 0:18). The overall changes of index of refraction after the exposure and annealing of as-deposited films reach values of 0.2. The values of the optical band gap, Eg , of the films were calculated from the a ¼ 0 intersects of 1=2 ðahmÞ vs. hm plots, where a is the absorption coefficient estimated according to [6], and hm is the photon energy. The error in determination of Eg values is evaluated as ±0.01 eV. The optical band gap values increase with decreasing energy of the laser beam (1.85–1.98 eV). After the exposure, values of the optical band gap increased, i.e., the photo-bleaching effect was observed; DEg ¼ Eg ðexposedÞ Eg ðas-depositedÞ ¼ 21–81 meV (Eg ¼ 1:87–2:06 eV) (Fig. 2). After subsequent annealing of the exposed films, values of the optical gap were found to be further increased, i.e., thermalbleaching effect was observed; DEg ¼ Eg ðannealedÞ Eg ðexposedÞ ¼ 190–250 meV (Eg ¼ 2:10–2:25 eV) (Fig. 2). The thickness of the films increases with exposure (photo-expansion up to 4.7% in comparison
P. Nemec et al. / Journal of Non-Crystalline Solids 326&327 (2003) 53–57
55
2.25
2.7 2.20
2.15
2.10
2.5
Eg / eV
Index of refraction
2.6
2.05
2.4 2.00
1.95
2.3
1.90
2.2 1.85
500
1000
1500
2000
2500
Wavelength / nm Fig. 1. Spectral dependencies of index of refraction of as-deposited, exposed, and annealed Ge–Ga–Se amorphous thin films prepared with different energy densities of laser beam used for PLD: full symbols – energy density of 1 J cm2 , half-filled symbols – energy density of 3 J cm2 , empty symbols – energy density of 5 J cm2 , squares – as-deposited films, circles – exposed films, triangles – annealed films.
with as-prepared films) and even with the annealing (thermal-expansion up to 5.4% in comparison with exposed films). In the photo-luminescence spectra of dysprosium doped Ge–Ga–Se thin films, two bands with maxima near 1140 and 1340 nm were observed (Fig. 3). Observed emission bands in near infrared spectral region can be connected with radiative electron transition between discrete energy levels of Dy3þ ions, as given in discussion. 4. Discussion As can be seen from the results given above, an increase of the thickness and of the optical band gap and decrease of the index of refraction were found for both exposed and annealed amorphous
1
2
3
4
5
Energy density / J.cm-2 Fig. 2. Optical band gap dependencies of as-deposited (squares), exposed (circles), and annealed (triangles) Ge–Ga–Se amorphous thin films on energy density of laser beam used for PLD.
Ge–Ga–Se thin films prepared at different energies of the laser beam used for PLD (Figs. 1 and 2). There is no evidence of compositional modifications due to the exposure and/or annealing of prepared films. Mentioned changes of thickness, optical band gap, and index of refraction occur simultaneously. We suppose that there is a direct relation between the changes of discussed parameters of thin films, i.e., larger values of optical band gap and lower values of index of refraction imply larger thickness of the films. The observed photo- and thermally-induced bleaching effect cannot be correlated with oxygen-assisted bond reconstruction and light induced surface oxidation proposed in [7] for obliquely deposited Ge-based chalcogenides because the preparation, exposure, and annealing of our thin films proceeded in vacuum or Ar atmosphere. Observed photo- and thermally-induced changes of thickness and optical band gap of studied
56
P. Nemec et al. / Journal of Non-Crystalline Solids 326&327 (2003) 53–57
3
Intensity / a.u.
2
1
0 1100
1200
1300
1400
1500
Wavelength / nm Fig. 3. Photo-luminescence spectra of as-deposited thin film prepared from (Ge30 Ga5 Se65 )99:5 (Dy2 Se3 )0:5 glass by PLD technique (energy density of laser beam 1 J cm2 ).
thin films show different behavior in comparison with Ge–Se thin films prepared by conventional evaporation technique. Kuzukawa et al. observed opposite relation, i.e., increase of the thickness implies decrease of optical band gap [8]. Such discrepancy can be probably explained by the different state of as-deposited amorphous thin films prepared using different techniques. Further research is necessary for more detailed explanation of this disagreement. The photo- and thermally-induced changes of optical band gap and index of refraction values of the thin films prepared by PLD are quite large (Dn up to 0.2, DEg up to 280 meV). Higher photo- and thermally-induced changes of optical parameters are probably connected with higher sensitivity of as-deposited PLD thin films. Higher sensitivity of as-deposited thin films results from the highly nonequilibrium state of thin films prepared by PLD technique. As we reported earlier, PLD technique can produce amorphous thin films with different
structure (in terms of different amounts of Ge–Ge (Ge–Ga or Ga–Ga), Se–Se, and Ge–Se (Ga–Se) bonds presented in films) depending on parameters of laser used for PLD [2]. We have found that with increasing energy density of laser beam, used for PLD, increases the amount of Ge–Ge (Ge–Ga or Ga–Ga) and Se–Se bonds (in comparison with bulk glasses) and hence the number of structural units containing these ÔwrongÕ bonds. Thin films prepared with higher energy density of the laser beam are thus further from the equilibrium state and their changes of properties when they are exposed and approaching the equilibrium should be higher. Two infrared emission bands with maxima near 1140 and 1340 nm, which were observed in the photo-luminescence spectra of dysprosium doped amorphous thin films to our knowledge for the first time, can be assigned to radiative electron transition between energy levels of Dy3þ ions. First emission band located at 1140 nm can be connected with radiative electron transitions 6 F9=2 , 6 H7=2 –6 H15=2 of Dy3þ ions in analogy with bulk chalcogenide glasses doped with dysprosium. Second emission band observed at 1340 nm corresponds probably with electron transitions 6 F11=2 , 6 H9=2 –6 H15=2 of Dy3þ ions [4]. Observed large photo- and thermally-induced changes of optical parameters of prepared amorphous Ge–Ga–Se thin films and reported infrared emission bands at 1140 and 1340 nm of dysprosium doped Ge–Ga–Se thin films are of large interest for potential applications in optoelectronics.
5. Conclusion PLD technique was used for preparation of pure and dysprosium-doped amorphous Ge–Ga– Se thin films. Photo- and thermally-induced changes of optical parameters (index of refraction, optical band gap) and the thickness of the films were studied. Emission spectra of dysprosium doped Ge–Ga–Se amorphous thin films were obtained and analyzed. Observed changes of optical parameters of studied Ge–Ga–Se films and infrared emission bands of dysprosium doped thin films can be interesting for potential applications in optoelectronics.
P. Nemec et al. / Journal of Non-Crystalline Solids 326&327 (2003) 53–57
Acknowledgements The work was supported by Ministry of Education of Czech Republic under the project LN 00A028 and by the project GA 203/00/0085 of Grant Agency of Czech Republic.
References [1] P. Nemec, M. Frumar, B. Frumarova, M. Jelınek, J. Lancok, J. Jedelsk y, Opt. Mat. 15 (2000) 191, and papers cited therein.
57
[2] P. Nemec, M. Frumar, J. Jedelsky, M. Jelınek, J. Lancok, I. Gregora, J. Non-Cryst. Solids 299–302 (2002) 1013. [3] M. De Sario, G. Leggieri, A. Luches, M. Martino, F. Prudenzano, A. Rizzo, Appl. Surf. Sci. 186 (2002) 216. [4] P. Nemec, B. Frumarova, M. Frumar, J. Oswald, J. Phys. Chem. Solids 61 (2000) 1583. [5] R. Swanepoel, J. Phys. E 16 (1983) 1214. [6] J. Tauc, in: J. Tauc (Ed.), Amorphous and Liquid Semiconductors, Plenum, New York, 1974. [7] C.A. Spence, S.R. Elliott, Phys. Rev. B 39 (1989) 39. [8] Y. Kuzukawa, A. Ganjoo, K. Shimakawa, J. Non-Cryst. Solids 227–230 (1998) 715.
On the optical properties of amorphous Ge–Ga–Se films prepared by pulsed laser deposition P. Nemec
a,*
, J. Jedelsk y a, M. Frumar a, M. Munzar b, M. Jelınek c, J. Lancok
c
a
b
Department of General and Inorganic Chemistry and Research Center, University of Pardubice, Legions Sq. 565, 53210 Pardubice, Czech Republic Joint Laboratory of Solid State Chemistry of the Acad. Sci. of the Czech Republic and the University of Pardubice, 532 10 Pardubice, Czech Republic c Institute of Physics of Acad. Sci. of the Czech Republic, Na Slovance 2, 18221 Prague, Czech Republic
Abstract Amorphous Ge–Ga–Se thin films (pure and dysprosium doped) were prepared by the pulsed laser deposition technique using different energy of the laser beam pulses. The effects of exposure and thermal annealing below the glass transition temperature on the optical parameters (index of refraction, optical band gap) and the thickness of asdeposited chalcogenide thin films were studied. The optical band gap and the thickness of the thin films increased with exposure of the films and even more with the annealing. Index of refraction has an opposite tendency. Two emission bands with maxima near 1140 and 1340 nm corresponding to 6 F9=2 , 6 H7=2 –6 H15=2 and 6 F11=2 , 6 H9=2 –6 H15=2 electron transitions of Dy3þ ions were identified in luminescence spectra of dysprosium doped thin films. Ó 2003 Elsevier B.V. All rights reserved. PACS: 78.20.Ci; 78.30.Hv; 78.40.Ha; 78.66.Jg; 81.15.Fg
1. Introduction Study of thin amorphous multicomponent chalcogenide films is of large interest, because of fundamental science reasons and also due to potential applications of such films in integrated planar optical circuits and their components for routing, amplifying or generating of optical signal (mainly in infrared spectral region), as well as in diffractive optics, in holography, for photo-resists
*
Corresponding author. Tel.: +420-466 037 265; fax: +420466 037 144. E-mail address: [email protected] (P. Nemec).
and optical memories production and for other optoelectronic applications [1,2]. There are several advantages of using pulsed laser deposition (PLD) (known also as laser ablation) for thin films preparation with respect to classical techniques: (i) chemical composition of the deposited film is mostly close to used targets; (ii) the possibility of deposition of multicomponent thin films without large changes of composition; (iii) short process time; and (iv) the control of PLD process by the laser parameters [1–3]. The main present disadvantages of the PLD are: (i) the difficulty in preparing films of larger areas, of even surface, and of equal thickness; (ii) the presence of droplets in the deposited films [1–3]; and (iii) more expensive
0022-3093/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0022-3093(03)00376-4
54
P. Nemec et al. / Journal of Non-Crystalline Solids 326&327 (2003) 53–57
facility. In this work, results of a study of the optical properties, and their photo- and thermallyinduced changes of thin films from the Ge–Ga–Se system prepared by PLD are presented; photoluminescence spectrum of Dy doped Ge–Ga–Se thin films is given and interpreted.
2. Experimental Amorphous germanium–gallium–selenide thin films were prepared by PLD using rotating targets of chalcogenide glasses with nominal composition of Ge30 Ga5 Se65 and (Ge30 Ga5 Se65 )99:5 (Dy2 Se3 )0:5 , respectively. The target glasses were prepared by conventional melt-quenching according to our previous report [4]. KrF excimer laser (Lumonics PM 840) operating at 248 nm with constant output energy of 500 mJ per pulse and with a repetition rate of 10 Hz was used for preparation of thin films. An optical attenuator varied the energy density of the laser beam on the target from 1 to 5 J cm2 . Amorphous thin films were deposited in a vacuum chamber (background pressure <102 Pa). The substrates used for PLD (chemically cleaned microscope glass slides) were positioned parallel to the target surface at a distance of 5 cm. All the films were deposited at room temperature. The chemical composition of the films was checked using wavelength dispersive X-ray analyzer (WDX), in particular an electron superprobe Jeol JXA 733 with a microanalyzer Kevex D. The room-temperature optical transmissivity spectra of the thin chalcogenide films were measured using the spectrophotometers Perkin–Elmer Lambda 9 (400–1100 nm) and Bio-Rad FTS 175C (1000–2700 nm). In order to determine photo-induced changes of optical parameters, prepared films (as-deposited) were exposed by high-pressure mercury lamp (200 W, 1 h) in an inert atmosphere of pure Ar. In order to evaluate thermally-induced changes of the optical properties, exposed films were annealed at 300 °C for 1 h in pure Ar. Photo-luminescence spectra of dysprosium doped Ge–Ga–Se thin films in near infrared spectral region (1080–1600 nm) were measured using
CW pump laser operating at 1064 nm (Nd:YAG) and liquid nitrogen cooled Ge detector. 3. Results Prepared films were homogeneous, of dark red color, with smooth surface as results from the from surface profile measurements. The chemical composition of the thin films was found to be close to the composition of used targets in analogy with our previous paper [2]. In the films prepared from dysprosium containing targets was identified also Dy; its content was measured only qualitatively. Spectral dependencies of the refractive index were calculated from the optical transmission spectra of as-deposited, exposed and annealed thin films using the Swanepoel method [5], examples (for three different energies of the laser beam used for PLD) are given in Fig. 1. The error in determination of index of refraction is evaluated as ±0.015. The index of refraction increases with increasing energy of the laser beam used for PLD (Fig. 1). Exposure of the as-deposited films caused the decrease of the values of indices of refraction (Dnmax ¼ 0:11). After annealing of exposed films, values of index of refraction were further decreased (Dnmax ¼ 0:18). The overall changes of index of refraction after the exposure and annealing of as-deposited films reach values of 0.2. The values of the optical band gap, Eg , of the films were calculated from the a ¼ 0 intersects of 1=2 ðahmÞ vs. hm plots, where a is the absorption coefficient estimated according to [6], and hm is the photon energy. The error in determination of Eg values is evaluated as ±0.01 eV. The optical band gap values increase with decreasing energy of the laser beam (1.85–1.98 eV). After the exposure, values of the optical band gap increased, i.e., the photo-bleaching effect was observed; DEg ¼ Eg ðexposedÞ Eg ðas-depositedÞ ¼ 21–81 meV (Eg ¼ 1:87–2:06 eV) (Fig. 2). After subsequent annealing of the exposed films, values of the optical gap were found to be further increased, i.e., thermalbleaching effect was observed; DEg ¼ Eg ðannealedÞ Eg ðexposedÞ ¼ 190–250 meV (Eg ¼ 2:10–2:25 eV) (Fig. 2). The thickness of the films increases with exposure (photo-expansion up to 4.7% in comparison
P. Nemec et al. / Journal of Non-Crystalline Solids 326&327 (2003) 53–57
55
2.25
2.7 2.20
2.15
2.10
2.5
Eg / eV
Index of refraction
2.6
2.05
2.4 2.00
1.95
2.3
1.90
2.2 1.85
500
1000
1500
2000
2500
Wavelength / nm Fig. 1. Spectral dependencies of index of refraction of as-deposited, exposed, and annealed Ge–Ga–Se amorphous thin films prepared with different energy densities of laser beam used for PLD: full symbols – energy density of 1 J cm2 , half-filled symbols – energy density of 3 J cm2 , empty symbols – energy density of 5 J cm2 , squares – as-deposited films, circles – exposed films, triangles – annealed films.
with as-prepared films) and even with the annealing (thermal-expansion up to 5.4% in comparison with exposed films). In the photo-luminescence spectra of dysprosium doped Ge–Ga–Se thin films, two bands with maxima near 1140 and 1340 nm were observed (Fig. 3). Observed emission bands in near infrared spectral region can be connected with radiative electron transition between discrete energy levels of Dy3þ ions, as given in discussion. 4. Discussion As can be seen from the results given above, an increase of the thickness and of the optical band gap and decrease of the index of refraction were found for both exposed and annealed amorphous
1
2
3
4
5
Energy density / J.cm-2 Fig. 2. Optical band gap dependencies of as-deposited (squares), exposed (circles), and annealed (triangles) Ge–Ga–Se amorphous thin films on energy density of laser beam used for PLD.
Ge–Ga–Se thin films prepared at different energies of the laser beam used for PLD (Figs. 1 and 2). There is no evidence of compositional modifications due to the exposure and/or annealing of prepared films. Mentioned changes of thickness, optical band gap, and index of refraction occur simultaneously. We suppose that there is a direct relation between the changes of discussed parameters of thin films, i.e., larger values of optical band gap and lower values of index of refraction imply larger thickness of the films. The observed photo- and thermally-induced bleaching effect cannot be correlated with oxygen-assisted bond reconstruction and light induced surface oxidation proposed in [7] for obliquely deposited Ge-based chalcogenides because the preparation, exposure, and annealing of our thin films proceeded in vacuum or Ar atmosphere. Observed photo- and thermally-induced changes of thickness and optical band gap of studied
56
P. Nemec et al. / Journal of Non-Crystalline Solids 326&327 (2003) 53–57
3
Intensity / a.u.
2
1
0 1100
1200
1300
1400
1500
Wavelength / nm Fig. 3. Photo-luminescence spectra of as-deposited thin film prepared from (Ge30 Ga5 Se65 )99:5 (Dy2 Se3 )0:5 glass by PLD technique (energy density of laser beam 1 J cm2 ).
thin films show different behavior in comparison with Ge–Se thin films prepared by conventional evaporation technique. Kuzukawa et al. observed opposite relation, i.e., increase of the thickness implies decrease of optical band gap [8]. Such discrepancy can be probably explained by the different state of as-deposited amorphous thin films prepared using different techniques. Further research is necessary for more detailed explanation of this disagreement. The photo- and thermally-induced changes of optical band gap and index of refraction values of the thin films prepared by PLD are quite large (Dn up to 0.2, DEg up to 280 meV). Higher photo- and thermally-induced changes of optical parameters are probably connected with higher sensitivity of as-deposited PLD thin films. Higher sensitivity of as-deposited thin films results from the highly nonequilibrium state of thin films prepared by PLD technique. As we reported earlier, PLD technique can produce amorphous thin films with different
structure (in terms of different amounts of Ge–Ge (Ge–Ga or Ga–Ga), Se–Se, and Ge–Se (Ga–Se) bonds presented in films) depending on parameters of laser used for PLD [2]. We have found that with increasing energy density of laser beam, used for PLD, increases the amount of Ge–Ge (Ge–Ga or Ga–Ga) and Se–Se bonds (in comparison with bulk glasses) and hence the number of structural units containing these ÔwrongÕ bonds. Thin films prepared with higher energy density of the laser beam are thus further from the equilibrium state and their changes of properties when they are exposed and approaching the equilibrium should be higher. Two infrared emission bands with maxima near 1140 and 1340 nm, which were observed in the photo-luminescence spectra of dysprosium doped amorphous thin films to our knowledge for the first time, can be assigned to radiative electron transition between energy levels of Dy3þ ions. First emission band located at 1140 nm can be connected with radiative electron transitions 6 F9=2 , 6 H7=2 –6 H15=2 of Dy3þ ions in analogy with bulk chalcogenide glasses doped with dysprosium. Second emission band observed at 1340 nm corresponds probably with electron transitions 6 F11=2 , 6 H9=2 –6 H15=2 of Dy3þ ions [4]. Observed large photo- and thermally-induced changes of optical parameters of prepared amorphous Ge–Ga–Se thin films and reported infrared emission bands at 1140 and 1340 nm of dysprosium doped Ge–Ga–Se thin films are of large interest for potential applications in optoelectronics.
5. Conclusion PLD technique was used for preparation of pure and dysprosium-doped amorphous Ge–Ga– Se thin films. Photo- and thermally-induced changes of optical parameters (index of refraction, optical band gap) and the thickness of the films were studied. Emission spectra of dysprosium doped Ge–Ga–Se amorphous thin films were obtained and analyzed. Observed changes of optical parameters of studied Ge–Ga–Se films and infrared emission bands of dysprosium doped thin films can be interesting for potential applications in optoelectronics.
P. Nemec et al. / Journal of Non-Crystalline Solids 326&327 (2003) 53–57
Acknowledgements The work was supported by Ministry of Education of Czech Republic under the project LN 00A028 and by the project GA 203/00/0085 of Grant Agency of Czech Republic.
References [1] P. Nemec, M. Frumar, B. Frumarova, M. Jelınek, J. Lancok, J. Jedelsk y, Opt. Mat. 15 (2000) 191, and papers cited therein.
57
[2] P. Nemec, M. Frumar, J. Jedelsky, M. Jelınek, J. Lancok, I. Gregora, J. Non-Cryst. Solids 299–302 (2002) 1013. [3] M. De Sario, G. Leggieri, A. Luches, M. Martino, F. Prudenzano, A. Rizzo, Appl. Surf. Sci. 186 (2002) 216. [4] P. Nemec, B. Frumarova, M. Frumar, J. Oswald, J. Phys. Chem. Solids 61 (2000) 1583. [5] R. Swanepoel, J. Phys. E 16 (1983) 1214. [6] J. Tauc, in: J. Tauc (Ed.), Amorphous and Liquid Semiconductors, Plenum, New York, 1974. [7] C.A. Spence, S.R. Elliott, Phys. Rev. B 39 (1989) 39. [8] Y. Kuzukawa, A. Ganjoo, K. Shimakawa, J. Non-Cryst. Solids 227–230 (1998) 715.