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Formation of heterostructure of A3B6 semiconductor compounds by surface laser modification
Optics and Lasers in Engineering 36 (2001) 299–302
Formation of heterostructure of A3B6 semiconductor compounds by surface laser modification Z. Gotraa,b, P. Stakhiraa, I. Tokareva, W. Proszakc,* a
Department of Electronic Devices, State University Lviv Polytechnic, 12 Bandera Street, Lviv 79013, Ukraine b Department of Electronic Systems, Rzeszo!w University of Technology, 2 W.Pola Street, Rzeszo!w, Poland c Department of Physics, Rzeszo!w University of Technology, 2 W.Pola Street, Rzeszo!w, Poland Received 20 November 2000; received in revised form 12 April 2001; accepted 14 April 2001
Abstract This article refers to our research results concerning creation of the oxide layers produced on the surface of GaSe crystals. These layers are obtained by the exposition of the samples in a pulsed laser beam. Measurements of the received layers were performed by a cathodoluminescence (CL) analysis method as well AES and XES methods. The spectrum was analyzed in the range of 1.2–4.5 eV. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: A3B6 semiconductor; Oxide layer; Heterostructure; Surface modification; Laser
1. Introduction Layered crystals, in particular the A3B6 compounds, are characterized by a significant anisotropy of electric and photo-electric properties. Moreover, the A3B6 semiconductor compounds are highly photo-sensitive in a wide spectral range. So it is very interesting to study the heterostructures on their basis, especially, the structures of the semiconductor-oxide type. [1–4]. But neither the oxide layers creation process on the surfaces of complex structures of selenide semiconductors with a layered structure nor the structural and phase composition and the properties of boundaries have been studied so far. So the present work is dedicated to studying *Corresponding author. E-mail address: [email protected] (W. Proszak). 0143-8166/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 3 - 8 1 6 6 ( 0 1 ) 0 0 0 4 5 - 8
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Z. Gotra et al. / Optics and Lasers in Engineering 36 (2001) 299–302
the creation process of oxide layers on the surface of a layered GaSe crystal under the influence of laser radiation.
2. Experimental procedure The studies were carried out on the samples of GaSe, which were made on the basis of crystals grown by Bridgman technique. The samples were made as 0.1– 0.3 mm thick flat-parallel plates, the bigger faces of which were parallel to a cleavage plane of a natural chip of the crystal (1 0 0). Laser oxidation of these plates was carried out in the air by a pulse nitric laser with a radiation wavelength of 3371 nm and pulse duration of 5 ns. The laser radiation energy density was limited to 1 J/cm2. In such conditions the pulse of laser radiation is absorbed by the surface layer of the crystal, which causes its local heating. Simultaneous cooling leads to consolidation of the structure changes that occur in a thin layer of the sample and to the heterostructure creation. For phase composition and laser-radiated layers homogenity studies the cathodoluminescence (CL) analysis techniques have been used. The CL was stimulated at the nitric temperature of the samples by electron pulses duration of 2 s, current density of the electron beam up to 1 mA/mm2 and energy of electrons of 2–10 keV. The radiation spectrum in the range 1.2–4.5 eV was recorded by means of a monochromator and photomultiplier. Additionally for the laser radiated layers analysis the AES and XES methods were used.
3. Results and discussion The CL spectrum for GaSe single crystals is characterized by a narrow intense stripe in the range from nitric to room temperatures, which is caused by a free exciton recombination [5]. The appearance of additional luminescence stripes is connected (according to Galiy et al. [6]) with structure defects. The influence of laser treatment in the air on luminescence properties of GaSe becomes significant at energy densities from 0.2 J/cm2 and becomes apparent in considerable CL intensity decrease, which corresponds to a free exciton (Fig. 1). For example, the CL intensity for GaSe crystals radiated by energy density of 0.7 J/cm2 (curve 3) is about 30 times lower than a CL intensity of a chiped surface. Such a character of CL is caused by the fact that when the temperature increases the GaSe surface absorption grows. As a consequence of this, the density of surface recombinations change significantly. This fact becomes apparent as the CL spectrum extinquishes. The increase in the laser radiation energy density to 1 J/cm2 leads to changes of the CL spectrum in the created oxide layers. In particular, it becomes apparent as a wide high-energy region, the maximum of which depends on laser treatment in the range 3.10–3.45 eV and the intensity grows along with radiation energy density increase (Fig. 2, curves 1,2). The low-energy part of the CL spectrum generally keeps the described character, which testifies to the presence of Ga2Se3 in the oxide layer. This fact is also confirmed
Z. Gotra et al. / Optics and Lasers in Engineering 36 (2001) 299–302
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Fig. 1. The GaSe CL spectrum (curve 1Fchiped surface; curve 2Fat a laser energy density of 0.2 J/cm2, and curve 3Fat a laser energy density of 0.7 J/cm2).
Fig. 2. CL spectrum of a laser oxidized GaSe layer (curve 1Fat a laser energy density of 0.5 J/cm2; curve 2Fat a laser energy density of 0.8 J/cm2, and curve 3Fchiped surface).
by the results of AES, by means of which the presence of selen on the surface of the oxide layer has been determined (it is obvious that this selen exists in the Ga2Se3 compound). The dependence of the intensity of the CL stripe of the oxide layer, which is formed on the surface of GaSe at irradiation density of 0.9 J/cm2, on the energy of the electron beam Ep is presented in Fig. 3. The intensity of the CL ultra-violet stripe (curve 1) hardly depends on electron energy in the range 2–10 keV. We did not discover any significant great dependence of Ep on the intensity of low-energy CL stripes that correspond to the presence of Ga2Se. The low-temperature part of the CL spectrum in the range 1.9–2.1 eV is presented in Fig. 3 (insertion). A considerable increase in its intensity along with an increase in the electron beam probing depth is observed for the stripe at 2.06 eV of the CL part of the spectrum (curve 2). The CL intensity at an energy of 2 eV is more uniform (curve 3). It indicates a slight decrease in the dopant amount in the oxide. The suboxides of Ga
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Z. Gotra et al. / Optics and Lasers in Engineering 36 (2001) 299–302
Fig. 3. The dependence of the intensity of the CL stripe of the oxide layer at energy of 0.8 J/cm2 on electron beam energy (curve 1Fultraviolet maximum; curve 2F2.6 eV, curve 3F2 eV. The insertion shows a low-energy part of the spectrum for the different Ep values. (curve 4Fat an energy of 10 keV; curve 5Fat an energy of 9.5 keV; curve 6Fat an energy of 8 keV, and curve 7Fat an energy of 7 keV).
such as Ga2O and GaO can be used as dopants. Such assumption is possible because the phase of Ga2O3 at GaSe oxidation can be formed sequentially through intermediate phases. These phases are unstable and we cannot register their existence by the method of CL or X-ray. Thus, the physico-chemical interaction of a clear GaSe surface with oxygen in the laser stimulated process can be determined by a complicated process of defect formation. The created layer consists of selenides and oxides of various compositions and is determined by diffusive motion of spot defects out of GaSe surface.
References [1] [2] [3] [4] [5] [6]
Anokin VZ, Linnik VD, Sysoeva EA. Surface 1991;2:155. Medvedkin GA, Amrazyavichus GA, Yanovenko AA. Surface 1987;2:81. Katerinchuk VN, Kovaluk MZ. Letters to JTP 1992;18:70. Beluch VM, Demkiv TM, Kavich VI, Savchin VP, Stakchira IM. Surface 1994;12:94. Williams RH, Evoy AI. Phys Status Solidi A 1972;12:277. Galiy PV, Nemchuk TM, Savchun VP, Stakchira IM. Ukrainian Phys J 1995;40:230.
Formation of heterostructure of A3B6 semiconductor compounds by surface laser modification Z. Gotraa,b, P. Stakhiraa, I. Tokareva, W. Proszakc,* a
Department of Electronic Devices, State University Lviv Polytechnic, 12 Bandera Street, Lviv 79013, Ukraine b Department of Electronic Systems, Rzeszo!w University of Technology, 2 W.Pola Street, Rzeszo!w, Poland c Department of Physics, Rzeszo!w University of Technology, 2 W.Pola Street, Rzeszo!w, Poland Received 20 November 2000; received in revised form 12 April 2001; accepted 14 April 2001
Abstract This article refers to our research results concerning creation of the oxide layers produced on the surface of GaSe crystals. These layers are obtained by the exposition of the samples in a pulsed laser beam. Measurements of the received layers were performed by a cathodoluminescence (CL) analysis method as well AES and XES methods. The spectrum was analyzed in the range of 1.2–4.5 eV. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: A3B6 semiconductor; Oxide layer; Heterostructure; Surface modification; Laser
1. Introduction Layered crystals, in particular the A3B6 compounds, are characterized by a significant anisotropy of electric and photo-electric properties. Moreover, the A3B6 semiconductor compounds are highly photo-sensitive in a wide spectral range. So it is very interesting to study the heterostructures on their basis, especially, the structures of the semiconductor-oxide type. [1–4]. But neither the oxide layers creation process on the surfaces of complex structures of selenide semiconductors with a layered structure nor the structural and phase composition and the properties of boundaries have been studied so far. So the present work is dedicated to studying *Corresponding author. E-mail address: [email protected] (W. Proszak). 0143-8166/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 3 - 8 1 6 6 ( 0 1 ) 0 0 0 4 5 - 8
300
Z. Gotra et al. / Optics and Lasers in Engineering 36 (2001) 299–302
the creation process of oxide layers on the surface of a layered GaSe crystal under the influence of laser radiation.
2. Experimental procedure The studies were carried out on the samples of GaSe, which were made on the basis of crystals grown by Bridgman technique. The samples were made as 0.1– 0.3 mm thick flat-parallel plates, the bigger faces of which were parallel to a cleavage plane of a natural chip of the crystal (1 0 0). Laser oxidation of these plates was carried out in the air by a pulse nitric laser with a radiation wavelength of 3371 nm and pulse duration of 5 ns. The laser radiation energy density was limited to 1 J/cm2. In such conditions the pulse of laser radiation is absorbed by the surface layer of the crystal, which causes its local heating. Simultaneous cooling leads to consolidation of the structure changes that occur in a thin layer of the sample and to the heterostructure creation. For phase composition and laser-radiated layers homogenity studies the cathodoluminescence (CL) analysis techniques have been used. The CL was stimulated at the nitric temperature of the samples by electron pulses duration of 2 s, current density of the electron beam up to 1 mA/mm2 and energy of electrons of 2–10 keV. The radiation spectrum in the range 1.2–4.5 eV was recorded by means of a monochromator and photomultiplier. Additionally for the laser radiated layers analysis the AES and XES methods were used.
3. Results and discussion The CL spectrum for GaSe single crystals is characterized by a narrow intense stripe in the range from nitric to room temperatures, which is caused by a free exciton recombination [5]. The appearance of additional luminescence stripes is connected (according to Galiy et al. [6]) with structure defects. The influence of laser treatment in the air on luminescence properties of GaSe becomes significant at energy densities from 0.2 J/cm2 and becomes apparent in considerable CL intensity decrease, which corresponds to a free exciton (Fig. 1). For example, the CL intensity for GaSe crystals radiated by energy density of 0.7 J/cm2 (curve 3) is about 30 times lower than a CL intensity of a chiped surface. Such a character of CL is caused by the fact that when the temperature increases the GaSe surface absorption grows. As a consequence of this, the density of surface recombinations change significantly. This fact becomes apparent as the CL spectrum extinquishes. The increase in the laser radiation energy density to 1 J/cm2 leads to changes of the CL spectrum in the created oxide layers. In particular, it becomes apparent as a wide high-energy region, the maximum of which depends on laser treatment in the range 3.10–3.45 eV and the intensity grows along with radiation energy density increase (Fig. 2, curves 1,2). The low-energy part of the CL spectrum generally keeps the described character, which testifies to the presence of Ga2Se3 in the oxide layer. This fact is also confirmed
Z. Gotra et al. / Optics and Lasers in Engineering 36 (2001) 299–302
301
Fig. 1. The GaSe CL spectrum (curve 1Fchiped surface; curve 2Fat a laser energy density of 0.2 J/cm2, and curve 3Fat a laser energy density of 0.7 J/cm2).
Fig. 2. CL spectrum of a laser oxidized GaSe layer (curve 1Fat a laser energy density of 0.5 J/cm2; curve 2Fat a laser energy density of 0.8 J/cm2, and curve 3Fchiped surface).
by the results of AES, by means of which the presence of selen on the surface of the oxide layer has been determined (it is obvious that this selen exists in the Ga2Se3 compound). The dependence of the intensity of the CL stripe of the oxide layer, which is formed on the surface of GaSe at irradiation density of 0.9 J/cm2, on the energy of the electron beam Ep is presented in Fig. 3. The intensity of the CL ultra-violet stripe (curve 1) hardly depends on electron energy in the range 2–10 keV. We did not discover any significant great dependence of Ep on the intensity of low-energy CL stripes that correspond to the presence of Ga2Se. The low-temperature part of the CL spectrum in the range 1.9–2.1 eV is presented in Fig. 3 (insertion). A considerable increase in its intensity along with an increase in the electron beam probing depth is observed for the stripe at 2.06 eV of the CL part of the spectrum (curve 2). The CL intensity at an energy of 2 eV is more uniform (curve 3). It indicates a slight decrease in the dopant amount in the oxide. The suboxides of Ga
302
Z. Gotra et al. / Optics and Lasers in Engineering 36 (2001) 299–302
Fig. 3. The dependence of the intensity of the CL stripe of the oxide layer at energy of 0.8 J/cm2 on electron beam energy (curve 1Fultraviolet maximum; curve 2F2.6 eV, curve 3F2 eV. The insertion shows a low-energy part of the spectrum for the different Ep values. (curve 4Fat an energy of 10 keV; curve 5Fat an energy of 9.5 keV; curve 6Fat an energy of 8 keV, and curve 7Fat an energy of 7 keV).
such as Ga2O and GaO can be used as dopants. Such assumption is possible because the phase of Ga2O3 at GaSe oxidation can be formed sequentially through intermediate phases. These phases are unstable and we cannot register their existence by the method of CL or X-ray. Thus, the physico-chemical interaction of a clear GaSe surface with oxygen in the laser stimulated process can be determined by a complicated process of defect formation. The created layer consists of selenides and oxides of various compositions and is determined by diffusive motion of spot defects out of GaSe surface.
References [1] [2] [3] [4] [5] [6]
Anokin VZ, Linnik VD, Sysoeva EA. Surface 1991;2:155. Medvedkin GA, Amrazyavichus GA, Yanovenko AA. Surface 1987;2:81. Katerinchuk VN, Kovaluk MZ. Letters to JTP 1992;18:70. Beluch VM, Demkiv TM, Kavich VI, Savchin VP, Stakchira IM. Surface 1994;12:94. Williams RH, Evoy AI. Phys Status Solidi A 1972;12:277. Galiy PV, Nemchuk TM, Savchun VP, Stakchira IM. Ukrainian Phys J 1995;40:230.