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Structural properties and interfacial layer formation of Pd films grown on InP substrates
Applied Surface Science 136 Ž1998. 117–122
Structural properties and interfacial layer formation of Pd films grown on InP substrates T.W. Kim
a,)
, Y.S. Yoon b, J.Y. Lee c , Y.H. Shin d , K.H. Yoo e, C.O. Kim
f
a
Department of Physics, Kwangwoon UniÕersity, 447-1 Wolgye-dong, Nowon-ku, Seoul 139-701 South Korea DiÕision of Ceramics, Korea Institute of the Science and Technology, P.O. Box 131, Cheongryang, Seoul, South Korea Department of Electronic Materials Engineering, Korea AdÕanced Institute of Science and Technology, Taejon 305-701, South Korea d Department of Electronic Engineering, Kyungwon UniÕersity, Bokjung, Sujung Gu, Seongnam, Kyung Ki-do, South Korea e Department of Physics, Kyung Hee UniÕersity, Seoul 137-701, South Korea f Department of Physics, Hanyang UniÕersity, Seoul 100-715, South Korea b
c
Received 31 October 1997; accepted 29 May 1998
Abstract Pd layers were grown on p-InP Ž100. substrates by the ion-beam-assisted deposition method with the goal of producing sharp Pdrp-InP heterostructure interfaces. X-ray diffraction measurements showed that the grown Pd layer was polycrystalline. Auger electron spectroscopy measurements showed that the composition of the as-grown film was Pd and that the PdrInP interface quality was relatively good. Transmission electron microscopy measurements showed that the grown Pd was a polycrystalline layer. The growth of polycrystalline Pd layers, instead of epitaxial films, originated from the formation of an interfacial amorphous layer prior to the creation of the Pd films. These results indicate that the Pd layers grown on p-InP Ž100. can be used for stable contacts in optoelectronic devices and high-speed field-effect transistors based on InP substrates and that the deposition of Pd on InP at room temperature might increase the barrier height of the resulting PdrInP Schottky diode. q 1998 Elsevier Science B.V. All rights reserved. PACS: 61.10.y i; 68.55.y a.
1. Introduction Recently, InP has been particularly interesting as a substrate for optoelectronic applications and highspeed electronic devices w1–5x because its use provides stable contacts with low contact resistances and low barrier heights, both of which are very important in these devices w6,7x. Also, the structural properties of the metal-semiconductor interfacial stages in the PdrInP heterostructures have very ef)
Corresponding author. Tel.: q82-02-940-5234; Fax: q82-02942-0108
fects on the buried gate in an InP metal-semiconductor field-effect transistor w8–11x. In addition, among the many metals that can be used to form Scottky barriers with InP, Pd is a very attractive metal because it enhances the barrier height w11x. Even though some works have been done on the growth of Pd films on InP substrates w8–11x, to the best of our knowledge, the growth of Pd epitaxial or polycrystalline films on InP Ž100. substrates has not yet been demonstrated due to inherent problems such as the lattice mismatch between the Pd and the InP. For these reasons, room-temperature deposition of Pd on InP substrates, as a means of looking for physical
0169-4332r98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 Ž 9 8 . 0 0 3 2 5 - 0
118
T.W. Kim et al.r Applied Surface Science 136 (1998) 117–122
evidence for a PdrInP heterostructure with interfacial abruptness, has been investigated. This paper reports the structural properties of Pd films grown on p-InP Ž100. substrates by ion-beam deposition ŽIBD. at room temperature, as well as those of the PdrInP interfaces. X-ray diffraction ŽXRD. measurements were performed to demonstrate the crystallinity of the grown layer, and Auger electron spectroscopy ŽAES. was carried out in order to characterize the stoichiometry of the grown films. Transmission electron microscopy ŽTEM. was performed to investigate the atomic structure of the Pd layer and the PdrInP interface.
2. Experimental The carrier concentration of the Zn-doped p-InP substrates with a Ž100. orientation used in this experiment was 1 = 10 16 cmy3 . The InP substrates obtained from Sumitomo were alternately degreased in warm acetone and trichloroethylene ŽTCE. three times, etched mechanochemically in a Br–methanol solution, rinsed thoroughly in deionized water, etched in a mixture of H 2 SO4 , H 2 O 2 , and H 2 O Ž4 : 1 : 1. at 408C for 10 min, and rinsed in TCE again. After the wafers were cleaned chemically, they were mounted
onto a susceptor in a deposition chamber. After the IBD chamber was evacuated to 1 = 10y6 Torr, the deposition was done at a substrate temperature of 300 K Žroom temperature.. In this case, a focused Arq beam was used to sputter a Pd-metal target. The deposition was done at a system pressure of 2 = 10y4 Torr, and the typical deposition rate was approxi˚ mately 1.7 Ars. The discharge voltage was 400 V, and the ion-gun was a cold hollow cathode. The bombarding ion energy and the ion-beam current were 1500 eV and 60 mA, respectively. The XRD measurements were performed using a Rigaku DrMax-B diffractometer with Cu K a radiation. The AES measurements were performed on the as-grown films using a Perkin-Elmer phi 400 scanning Auger microprobe. The TEM observations were performed in a JEOL 200CX transmission electron microscope operating at 400 kV. The samples for the TEM measurements were prepared by cutting and polishing with diamond paper to an approximately 30-mm thickness, and then argon-ion milling at liquid-nitrogen temperature to electron transparency. 3. Results and discussion The as-grown Pd films prepared by IBD had mirror-like surfaces without any indication of pin-
Fig. 1. An X-ray diffraction pattern for a Pd film grown on an InP Ž100. substrate.
T.W. Kim et al.r Applied Surface Science 136 (1998) 117–122
119
Fig. 2. Auger electron spectroscopy results obtained from the PdrInP structure. The lower curve was obtained at the Pd surface, and the ˚ respectively. middle and the upper curves were obtained at depths of 500 and 3000 A,
holes and microcracks, which were confirmed using Nomarski optical microscopy. Scanning electron microscopy measurements also indicated a mirror-like
surface morphology. Fig. 1 shows the XRD pattern for a PdrInP heterostructure. The Ž111. and the Ž200. K a 1 diffraction peaks of the Pd together with
Fig. 3. Auger depth profile of the PdrInP structure.
120
T.W. Kim et al.r Applied Surface Science 136 (1998) 117–122
Fig. 4. A bright-field transmission electron microscopy image of the PdrInP structure.
the InP Ž200. peak are clearly observed. In particular, the Ž111. and the Ž200. K a 1 diffraction peaks of the Pd are consistent with the XRD lines from a Pd film grown on a Ž100.-oriented InP substrate by thermal evaporation w10x. These results indicate that a Pd polycrystalline film can be grown on a InP Ž100. substrate using the IBD technique. The results of the AES measurements showed that the as-grown film consisted of Pd and carbon at the ˚ depth, as sample surface and of only Pd at a 500-A shown in the lower and the middle curves of Fig. 2, respectively. The PdrInP sample consisted of In and ˚ depth, as shown in the upper curve of P at a 3000-A Fig. 2. The existence of the carbon impurity at the sample surface could be due to contamination from the atmosphere after the Pd thin film growth. Fig. 3 shows that the compositional profile of the interface between the Pd and the InP was relatively sharp and that a little Pd, In, and P interdiffused into each layer. The few In and P atoms penetrated the Pd layer due to partial dissolution in spite of the relatively flat heterojunction w12x. The interface quality of the PdrInP heterostructure is sharper than that reported in the other literatures w11,12x, and the Pd composition of the as-grown film is with more uniform distribution throughout the thickness of the film in comparison with that grown by a thermal evaporation method w11x. Even though an interdiffusion or intermixing problem appeared at the Pdrp-InP heterostructure interface, the interfacial reaction be-
tween the Pd and the InP due to thermal damage could be neglected w13x. The driving force for the partial dissolution is induced by the incident energetic atoms. Even though it is impossible to explain unambiguously from the AES measurements why this interfacial layer is created, the formation of an interfacial amorphous layer might result from the intermixing of the interface due to the bombardment of the surface by the incident energetic atoms. The
Fig. 5. An electron-diffraction pattern from transmission electron microscopy of the Pd layer.
T.W. Kim et al.r Applied Surface Science 136 (1998) 117–122
121
cal properties and annealing behaviors of the PdrInP heterostructures will be still investigated in future.
4. Summary and conclusions
Fig. 6. An electron-diffraction pattern from transmission electron microscopy of the PdrInP structure, with Ž hlk . P and Ž hlk . I corresponding to the Pd and the InP indexes of the reciprocal vectors, respectively.
The results of XRD, AES, and TEM measurements show that the layers grown by IBD were Pd polycrystalline films. AES measurements show that the as-grown films have uniform compositions throughout the films and relatively sharp PdrInP heterointerfaces. TEM measurements show that an interfacial layer is formed between the polycrystalline Pd layer and the InP substrates. With careful growth of the Pd thin film on a p-InP substrate, it should be possible to produce a PdrInP heterostructure with a very sharp interface. Furthermore, high quality Pd films hold promise for applications in optoelectronic devices and high speed field-effect transistors based on InP substrates.
Acknowledgements
˚ and this thickness of Pd was approximately 1800 A, value was in good agreement with that determined from ellipsometry measurements. The bright-field TEM in Fig. 4 shows the interfacial layer between the top Pd layer and the bottom InP substrate. The Pd thin layer has a very smooth surface without any stacking faults and dislocations. The electron diffraction pattern from the Pd thin layer shows weak spots and rings, as shown in Fig. 5. Since the small spots corresponding to the Pd are not symmetrical, the Pd layer is a polycrystalline film. Selected-area electron-diffraction patterns from TEM measurements at the PdrInP heterointerface are shown in Fig. 6. The strong and regular spots originate from the InP substrate, and the weak irregular spots and the diffusion of the rings corresponding to the Ž111. peaks are due to the Pd polycrystalline film and the amorphous interfacial layer w14x, respectively. The formation of an interfacial layer, such as Pd 2 InP, in the initial stage of film growth prevents the growth of a Pd epitaxial film w12x. However, the Pd thin films grown on p-InP Ž100. substrates by the IBD technique might enhance the rectifying properties of the PdrInP diodes w15x. The detailed electri-
This work at Kwangwoon University was supported by the Basic Science Research Institute Program, Ministry of Education, 1998, Project No. BSRI-97-2423, and the work at Kyung Hee University was supported by the Basic Science Research Institute Program Ministry of Education, 1998, Project No. BSRI-97-2443.
References w1x C.W. Wilmsen, Physics and Chemistry of III–V Compound Semiconductor Interfaces, Plenum, New York, 1985. w2x F. Capasso, Physics of Quantum Electron Devices, SpringerVerlag, Heidelberg, 1990. w3x C. Weisbuch, B. Vinter, Quantum Semiconductor Structures, Academic Press, Boston, 1991. w4x T.W. Kim, S.S. Yom, Appl. Phys. Lett. 65 Ž1994. 1955. w5x M.-H. Park, L.C. Wang, J.Y. Cheng, F. Deng, S.S. Lau, C.J. Palmstrom, Appl. Phys. Lett. 68 Ž1996. 952. w6x C.F. Lin, S.E. Mohney, Y.A. Chang, J. Appl. Phys. 74 Ž1993. 4398. w7x T.W. Kim, Y.S. Yoon, J.Y. Lee, Appl. Phys. Lett. 69 Ž1996. 972. w8x Z.Q. Shi, R.L. Wallace, W.A. Anderson, Appl. Phys. Lett. 59 Ž1991. 446.
122
T.W. Kim et al.r Applied Surface Science 136 (1998) 117–122
w9x D.G. Ivey, P. Jian, R. Bruce, J. Electron. Mater. 21 Ž1992. 831. w10x H.F. Chuang, C.P. Lee, J.S. Tsang, J.C. Fan, J. Appl. Phys. 80 Ž1996. 2891. w11x J.W. Palmer, W.A. Anderson, D.T. Hoelzer, M. Thomas, J. Electron. Mater. 25 Ž1996. 1645.
w12x R.C. Popowich, J. Washburn, T. Sands, A.S. Kaplan, J. Appl. Phys. 64 Ž1988. 4909. w13x S.E. Mohney, Y. Chang, J. Appl. Phys. 74 Ž1993. 4403. w14x T.W. Kim, Y.S. Yoon, S.S. Yom, J.Y. Lee, Appl. Phys. Lett. 64 Ž1994. 2676. w15x E. Hokelek, G.Y. Robinson, Appl. Phys. Lett. 40 Ž1982. 426. ¨
Structural properties and interfacial layer formation of Pd films grown on InP substrates T.W. Kim
a,)
, Y.S. Yoon b, J.Y. Lee c , Y.H. Shin d , K.H. Yoo e, C.O. Kim
f
a
Department of Physics, Kwangwoon UniÕersity, 447-1 Wolgye-dong, Nowon-ku, Seoul 139-701 South Korea DiÕision of Ceramics, Korea Institute of the Science and Technology, P.O. Box 131, Cheongryang, Seoul, South Korea Department of Electronic Materials Engineering, Korea AdÕanced Institute of Science and Technology, Taejon 305-701, South Korea d Department of Electronic Engineering, Kyungwon UniÕersity, Bokjung, Sujung Gu, Seongnam, Kyung Ki-do, South Korea e Department of Physics, Kyung Hee UniÕersity, Seoul 137-701, South Korea f Department of Physics, Hanyang UniÕersity, Seoul 100-715, South Korea b
c
Received 31 October 1997; accepted 29 May 1998
Abstract Pd layers were grown on p-InP Ž100. substrates by the ion-beam-assisted deposition method with the goal of producing sharp Pdrp-InP heterostructure interfaces. X-ray diffraction measurements showed that the grown Pd layer was polycrystalline. Auger electron spectroscopy measurements showed that the composition of the as-grown film was Pd and that the PdrInP interface quality was relatively good. Transmission electron microscopy measurements showed that the grown Pd was a polycrystalline layer. The growth of polycrystalline Pd layers, instead of epitaxial films, originated from the formation of an interfacial amorphous layer prior to the creation of the Pd films. These results indicate that the Pd layers grown on p-InP Ž100. can be used for stable contacts in optoelectronic devices and high-speed field-effect transistors based on InP substrates and that the deposition of Pd on InP at room temperature might increase the barrier height of the resulting PdrInP Schottky diode. q 1998 Elsevier Science B.V. All rights reserved. PACS: 61.10.y i; 68.55.y a.
1. Introduction Recently, InP has been particularly interesting as a substrate for optoelectronic applications and highspeed electronic devices w1–5x because its use provides stable contacts with low contact resistances and low barrier heights, both of which are very important in these devices w6,7x. Also, the structural properties of the metal-semiconductor interfacial stages in the PdrInP heterostructures have very ef)
Corresponding author. Tel.: q82-02-940-5234; Fax: q82-02942-0108
fects on the buried gate in an InP metal-semiconductor field-effect transistor w8–11x. In addition, among the many metals that can be used to form Scottky barriers with InP, Pd is a very attractive metal because it enhances the barrier height w11x. Even though some works have been done on the growth of Pd films on InP substrates w8–11x, to the best of our knowledge, the growth of Pd epitaxial or polycrystalline films on InP Ž100. substrates has not yet been demonstrated due to inherent problems such as the lattice mismatch between the Pd and the InP. For these reasons, room-temperature deposition of Pd on InP substrates, as a means of looking for physical
0169-4332r98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 Ž 9 8 . 0 0 3 2 5 - 0
118
T.W. Kim et al.r Applied Surface Science 136 (1998) 117–122
evidence for a PdrInP heterostructure with interfacial abruptness, has been investigated. This paper reports the structural properties of Pd films grown on p-InP Ž100. substrates by ion-beam deposition ŽIBD. at room temperature, as well as those of the PdrInP interfaces. X-ray diffraction ŽXRD. measurements were performed to demonstrate the crystallinity of the grown layer, and Auger electron spectroscopy ŽAES. was carried out in order to characterize the stoichiometry of the grown films. Transmission electron microscopy ŽTEM. was performed to investigate the atomic structure of the Pd layer and the PdrInP interface.
2. Experimental The carrier concentration of the Zn-doped p-InP substrates with a Ž100. orientation used in this experiment was 1 = 10 16 cmy3 . The InP substrates obtained from Sumitomo were alternately degreased in warm acetone and trichloroethylene ŽTCE. three times, etched mechanochemically in a Br–methanol solution, rinsed thoroughly in deionized water, etched in a mixture of H 2 SO4 , H 2 O 2 , and H 2 O Ž4 : 1 : 1. at 408C for 10 min, and rinsed in TCE again. After the wafers were cleaned chemically, they were mounted
onto a susceptor in a deposition chamber. After the IBD chamber was evacuated to 1 = 10y6 Torr, the deposition was done at a substrate temperature of 300 K Žroom temperature.. In this case, a focused Arq beam was used to sputter a Pd-metal target. The deposition was done at a system pressure of 2 = 10y4 Torr, and the typical deposition rate was approxi˚ mately 1.7 Ars. The discharge voltage was 400 V, and the ion-gun was a cold hollow cathode. The bombarding ion energy and the ion-beam current were 1500 eV and 60 mA, respectively. The XRD measurements were performed using a Rigaku DrMax-B diffractometer with Cu K a radiation. The AES measurements were performed on the as-grown films using a Perkin-Elmer phi 400 scanning Auger microprobe. The TEM observations were performed in a JEOL 200CX transmission electron microscope operating at 400 kV. The samples for the TEM measurements were prepared by cutting and polishing with diamond paper to an approximately 30-mm thickness, and then argon-ion milling at liquid-nitrogen temperature to electron transparency. 3. Results and discussion The as-grown Pd films prepared by IBD had mirror-like surfaces without any indication of pin-
Fig. 1. An X-ray diffraction pattern for a Pd film grown on an InP Ž100. substrate.
T.W. Kim et al.r Applied Surface Science 136 (1998) 117–122
119
Fig. 2. Auger electron spectroscopy results obtained from the PdrInP structure. The lower curve was obtained at the Pd surface, and the ˚ respectively. middle and the upper curves were obtained at depths of 500 and 3000 A,
holes and microcracks, which were confirmed using Nomarski optical microscopy. Scanning electron microscopy measurements also indicated a mirror-like
surface morphology. Fig. 1 shows the XRD pattern for a PdrInP heterostructure. The Ž111. and the Ž200. K a 1 diffraction peaks of the Pd together with
Fig. 3. Auger depth profile of the PdrInP structure.
120
T.W. Kim et al.r Applied Surface Science 136 (1998) 117–122
Fig. 4. A bright-field transmission electron microscopy image of the PdrInP structure.
the InP Ž200. peak are clearly observed. In particular, the Ž111. and the Ž200. K a 1 diffraction peaks of the Pd are consistent with the XRD lines from a Pd film grown on a Ž100.-oriented InP substrate by thermal evaporation w10x. These results indicate that a Pd polycrystalline film can be grown on a InP Ž100. substrate using the IBD technique. The results of the AES measurements showed that the as-grown film consisted of Pd and carbon at the ˚ depth, as sample surface and of only Pd at a 500-A shown in the lower and the middle curves of Fig. 2, respectively. The PdrInP sample consisted of In and ˚ depth, as shown in the upper curve of P at a 3000-A Fig. 2. The existence of the carbon impurity at the sample surface could be due to contamination from the atmosphere after the Pd thin film growth. Fig. 3 shows that the compositional profile of the interface between the Pd and the InP was relatively sharp and that a little Pd, In, and P interdiffused into each layer. The few In and P atoms penetrated the Pd layer due to partial dissolution in spite of the relatively flat heterojunction w12x. The interface quality of the PdrInP heterostructure is sharper than that reported in the other literatures w11,12x, and the Pd composition of the as-grown film is with more uniform distribution throughout the thickness of the film in comparison with that grown by a thermal evaporation method w11x. Even though an interdiffusion or intermixing problem appeared at the Pdrp-InP heterostructure interface, the interfacial reaction be-
tween the Pd and the InP due to thermal damage could be neglected w13x. The driving force for the partial dissolution is induced by the incident energetic atoms. Even though it is impossible to explain unambiguously from the AES measurements why this interfacial layer is created, the formation of an interfacial amorphous layer might result from the intermixing of the interface due to the bombardment of the surface by the incident energetic atoms. The
Fig. 5. An electron-diffraction pattern from transmission electron microscopy of the Pd layer.
T.W. Kim et al.r Applied Surface Science 136 (1998) 117–122
121
cal properties and annealing behaviors of the PdrInP heterostructures will be still investigated in future.
4. Summary and conclusions
Fig. 6. An electron-diffraction pattern from transmission electron microscopy of the PdrInP structure, with Ž hlk . P and Ž hlk . I corresponding to the Pd and the InP indexes of the reciprocal vectors, respectively.
The results of XRD, AES, and TEM measurements show that the layers grown by IBD were Pd polycrystalline films. AES measurements show that the as-grown films have uniform compositions throughout the films and relatively sharp PdrInP heterointerfaces. TEM measurements show that an interfacial layer is formed between the polycrystalline Pd layer and the InP substrates. With careful growth of the Pd thin film on a p-InP substrate, it should be possible to produce a PdrInP heterostructure with a very sharp interface. Furthermore, high quality Pd films hold promise for applications in optoelectronic devices and high speed field-effect transistors based on InP substrates.
Acknowledgements
˚ and this thickness of Pd was approximately 1800 A, value was in good agreement with that determined from ellipsometry measurements. The bright-field TEM in Fig. 4 shows the interfacial layer between the top Pd layer and the bottom InP substrate. The Pd thin layer has a very smooth surface without any stacking faults and dislocations. The electron diffraction pattern from the Pd thin layer shows weak spots and rings, as shown in Fig. 5. Since the small spots corresponding to the Pd are not symmetrical, the Pd layer is a polycrystalline film. Selected-area electron-diffraction patterns from TEM measurements at the PdrInP heterointerface are shown in Fig. 6. The strong and regular spots originate from the InP substrate, and the weak irregular spots and the diffusion of the rings corresponding to the Ž111. peaks are due to the Pd polycrystalline film and the amorphous interfacial layer w14x, respectively. The formation of an interfacial layer, such as Pd 2 InP, in the initial stage of film growth prevents the growth of a Pd epitaxial film w12x. However, the Pd thin films grown on p-InP Ž100. substrates by the IBD technique might enhance the rectifying properties of the PdrInP diodes w15x. The detailed electri-
This work at Kwangwoon University was supported by the Basic Science Research Institute Program, Ministry of Education, 1998, Project No. BSRI-97-2423, and the work at Kyung Hee University was supported by the Basic Science Research Institute Program Ministry of Education, 1998, Project No. BSRI-97-2443.
References w1x C.W. Wilmsen, Physics and Chemistry of III–V Compound Semiconductor Interfaces, Plenum, New York, 1985. w2x F. Capasso, Physics of Quantum Electron Devices, SpringerVerlag, Heidelberg, 1990. w3x C. Weisbuch, B. Vinter, Quantum Semiconductor Structures, Academic Press, Boston, 1991. w4x T.W. Kim, S.S. Yom, Appl. Phys. Lett. 65 Ž1994. 1955. w5x M.-H. Park, L.C. Wang, J.Y. Cheng, F. Deng, S.S. Lau, C.J. Palmstrom, Appl. Phys. Lett. 68 Ž1996. 952. w6x C.F. Lin, S.E. Mohney, Y.A. Chang, J. Appl. Phys. 74 Ž1993. 4398. w7x T.W. Kim, Y.S. Yoon, J.Y. Lee, Appl. Phys. Lett. 69 Ž1996. 972. w8x Z.Q. Shi, R.L. Wallace, W.A. Anderson, Appl. Phys. Lett. 59 Ž1991. 446.
122
T.W. Kim et al.r Applied Surface Science 136 (1998) 117–122
w9x D.G. Ivey, P. Jian, R. Bruce, J. Electron. Mater. 21 Ž1992. 831. w10x H.F. Chuang, C.P. Lee, J.S. Tsang, J.C. Fan, J. Appl. Phys. 80 Ž1996. 2891. w11x J.W. Palmer, W.A. Anderson, D.T. Hoelzer, M. Thomas, J. Electron. Mater. 25 Ž1996. 1645.
w12x R.C. Popowich, J. Washburn, T. Sands, A.S. Kaplan, J. Appl. Phys. 64 Ž1988. 4909. w13x S.E. Mohney, Y. Chang, J. Appl. Phys. 74 Ž1993. 4403. w14x T.W. Kim, Y.S. Yoon, S.S. Yom, J.Y. Lee, Appl. Phys. Lett. 64 Ž1994. 2676. w15x E. Hokelek, G.Y. Robinson, Appl. Phys. Lett. 40 Ž1982. 426. ¨