- Email: [email protected]
Piezospectroscopic analysis of the Pt–H2 complex in silicon
ARTICLE IN PRESS
Physica B 340–342 (2003) 677–681
Piezospectroscopic analysis of the Pt–H2 complex in silicon V. Kolkovskia,*, O. Andersenb, L. Dobaczewskia, A.R. Peakerb, K. Bonde Nielsenc a
Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland b Centre for Electronic Materials, Devices and Nanostructures, UMIST, Manchester, UK c Institute of Physics and Astronomy, University of Aarhus, Aarhus, Denmark
Abstract In this study the use of the high-resolution Laplace DLTS combined with uniaxial stress has allowed us to investigate in detail the structure and electrical properties of the platinum–hydrogen-related complex PtH2. We correlate the defect electronic level with the results of other spectroscopic studies performed with electron paramagnetic resonance and farinfrared absorption measurements. The observed stress-induced peak splitting pattern confirms the orthorhombic-IC2v symmetry of the complex. The re-orientation process of the defect can be observed at temperatures higher than the room temperature for all bias conditions. r 2003 Elsevier B.V. All rights reserved. PACS: 61.72.Ji; 71.55.Cn; 71.70.Ft Keywords: Platinum–hydrogen complex; Laplace DLTS; Piezospectroscopy
Defects and complexes related to transition metals (TM) in silicon still remain an important topic for research. They act as an effective tool for minority carrier lifetime control in semiconductor power devices. Hydrogen is known to be one of the most common unintentional impurities in silicon. It interacts with TM and can result in either passivation of the associated deep levels, i.e. a disappearance of the electrical activity of the TM in the crystal (in early studies only complete passivation electrically active complexes by hydrogen was reported), or in the formation of electrically active TM–hydrogen complexes. As a result of this, the effect of hydrogen on the electrical properties of TM in silicon, especially *Corresponding author. Fax: +48-847-5223. E-mail address: [email protected] (V. Kolkovski).
the formation of electrically active complexes, has been studied by means of electron paramagnetic resonance (EPR) [1,2], deep level transient spectroscopy (DLTS) combined with depth-profile or annealing studies [3–8] and local vibrational mode (LVM) spectroscopy [9–11]. These techniques have provided valuable information about the position of the TM–H levels in the band gap, their electron and hole capture cross sections, the numbers of hydrogen atoms involved as well as their positions within the structure of the defects. The interaction of hydrogen and platinum in silicon has been the subject of several reports [12–15]. DLTS measurements combined with depth-profiling and annealing studies showed that platinum forms several complexes after hydrogenation by wet-chemical etching. Four platinum–hydrogen related deep levels have been
0921-4526/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2003.09.164
ARTICLE IN PRESS V. Kolkovski et al. / Physica B 340–342 (2003) 677–681
identified E(90), E(250) in n-type silicon and H(150), H(210) in p-type silicon. It has been proposed [3,14] that the origin of another DLTS peak, E(90), is a PtH2 centre, however, there was no direct evidence connecting this peak with the PtH2 complex which was observed by EPR. Fukuda et al. [15] resolved this issue by applying conventional DLTS combined with uniaxial stress. They demonstrated that the stress splitting is consistent with orthorhombic-I symmetry of PtH2 in agreement with the results of EPR, LVM and theoretical calculations. However, because a defect re-orientation process is observed in Ref. [15] at temperatures about 90 K it has been concluded that the alignment process for the PtH2 complex is even more efficient than for the case of the vacancy–oxygen (VO) pair. In our study we correlate the sample processing procedure with energy level corresponding to the PtH2 complex. Using high-resolution Laplace DLTS (LDLTS) [16] combined with uniaxial stress we confirm that the structure of this defect is orthorhombic. The influence of uniaxial stress on the ionisation process has been studied for different orientations of the stress in relation to the crystallographic directions and it has been concluded that the effect of stress on the process is rather weak in comparison to that already observed for the case of VO [17], the divacancy (V2) [18], and the carbon–hydrogen pair [19] in the n-type silicon. We also have observed that in our samples the defect re-orientation process apparent as a stress-induced alignment effect only occurs at temperatures higher than 300 K. This is the case for both charge states of the PtH2 centre and, in this respect, does not agree with the findings reported in Ref. [15]. The samples for this study have been prepared from the (1 0 0)-oriented phosphorous-doped floatzone grown silicon with a resistivity of 21–23 Ocm. The samples were cut into 7 2 1 mm3 bars with the long dimension parallel to one of the major crystallographic directions /1 0 0S, /1 1 0S or /1 1 1S. A thin platinum layer was evaporated onto one side of silicon wafer and diffused in at B820 C for 2 h in a nitrogen atmosphere. The samples were etched for 2 min in CP4A solution in order to introduce hydrogen and eliminate the
high surface concentration of platinum resulting from the U-shape of the in-diffused TM. Additional hydrogen has been introduced during a 30 min soak in a solution of nitric (70%) and hydrofluoric (48%) acids in a 10:1 ratio. The Schottky diodes were formed by vacuum evaporation of gold on the polished and etched side of the wafer. An eutectic InGa alloy was rubbed onto the back side of the samples to fabricate an Ohmic contact. A series of test samples made on randomly oriented pieces of the same wafers according to the procedure described has also been produced for calibration of the platinum and hydrogen diffusion process. Fig. 1 shows typical conventional DLTS spectra for three test samples prepared from the same crystal. The spectra depicted in Fig. 1 were recorded directly after the wet-chemical etching. Three dominant DLTS peaks are observed at 100, 120 and 270 K. These peaks are detected in all platinum and hydrogen diffused n-type samples. The peak at 120 K is a well-known acceptor state of the isolated substitutional platinum atom. Two other peaks at 100 and 270 K have been assigned as related to PtH2 and PtH, respectively [3]. The introduction of atomic hydrogen via the
Si FZ Pt-diffusion 30 mins and etching DLTS signal (arb. units)
678
PtH
Pt(-/0) 850 C 820 C 775 C
PtH 2
100
150
200
250
300
Temperature (K) Fig. 1. The conventional DLTS spectra of Pt-doped n-type float zone Si after a 30 min Pt-diffusion at different diffusion temperatures followed the wet-chemical etching which introduces hydrogen.
ARTICLE IN PRESS V. Kolkovski et al. / Physica B 340–342 (2003) 677–681
Si: PtH2 T=90K Laplace DLTS amplitude (arb. units)
wet-chemical etching procedure has the disadvantage that the amount of hydrogen introduced into the crystal cannot be monitored precisely. However, this procedure allows the concentration of hydrogen to be reproduced when the etching procedure is carefully repeated. As seen in the figure, an increase of the platinum diffusion temperature results in an increase of the platinum concentration while the wet-etching procedure introduces in each case a similar amount of hydrogen. As a result, the ratio between the PtH2 and other peaks, i.e. Pt and PtH, decreases showing that hydrogen has a tendency to decorate the platinum atoms. No deep levels have been detected using either Laplace or conventional DLTS spectra in reference samples not diffused with platinum. The electronic level corresponding to the PtH2 complex and related to the peak at 100 K is characterised by the capture cross section sn ¼ 9 1016 cm2 (evaluated from the filling pulse method) and the activation energy of the emission Et ¼ Ec 0:159 eV. These values agree, within reasonable error limits, with the ones reported in Ref. [15]. As mentioned above, the structure of the stable PtH2 complex established by EPR has the orthorhombic-I C2v symmetry. Thus, the defect has two non-equivalent orientations of degeneracy 2 and 4 for stress along the /1 0 0S direction, three non-equivalent orientations of degeneracy 1, 4 and 1 for stress along the /1 1 0S direction, and finally two non-equivalent orientations of degeneracy 3 and 3 for stress along /1 1 1S direction. Fig. 2 shows the 90 K Laplace DLTS spectra of PtH2 obtained at zero stress and under uniaxial stress along the three major crystallographic directions. For each stress-direction, the zero-stress peak splits into two well-resolved peaks. The amplitudes of the split lines sum up to the amplitude of the zero-stress peak. The experimental amplitude ratios of the individual peaks in Fig. 2 agree to within 10% of the ratios expected for an orthorhombic-I centre, i.e. 2:4 for the /1 0 0S stress direction, (1+4):1 for the /1 1 0S stress direction (note a broadened larger peak, which could be a result of the unresolved additional splitting) and 3:3 for the /1 1 1S stress direction.
679
<111> 0.20GPa
<110> 0.23GPa
<100> 0.15GPa
0GPa
1
10
Emission rate
100
(s-1)
Fig. 2. Laplace DLTS spectra of PtH2 obtained at zero stress and under uniaxial stress along the three major crystallographic directions, /1 0 0S, /1 1 0S and /1 1 1S. The splitting pattern confirms the orthorhombic-I symmetry of the PtH2 complex.
According to our observations, the PtH2 complex only starts to re-orientate at temperatures above 300 K. When the sample bias is applied (and consequently adding an electron to the PtH2 centre) this re-orientation temperature needs to be a little higher than the one for the bias off conditions. This is in agreement to a general trend observed, for example, in the vacancy–oxygen [17] and the vacancy–oxygen–hydrogen [20] complexes, where it has been found that the reorientation barrier increases when there are more electrons captured by a complex. The re-orientation barriers of vacancy-involving orthorhombic (VO) and pseudo-orthorhombic (VOH) complexes are 0.38 and 0.56 eV, respectively. In consequence these defects start to re-orientate (in a time scale of minutes) at temperatures around 100 and 200 K for VO and VOH, respectively. In the PtH2 complex no vacancies are involved and so in principle it might be expected that the lack of
ARTICLE IN PRESS 680
V. Kolkovski et al. / Physica B 340–342 (2003) 677–681
empty volume in the unit cell could make the reorientation process much more difficult. As a result, the re-orientation barrier would be expected to be much higher than the one observed in the former two cases. On the other hand, it has been already observed that the divacancy in silicon only starts to re-orientate at temperatures above 350 K and in this case this process is thought to be identical with the long-range diffusion of the complex [18]. The diffusion of the divacancy is governed by a 1.3 eV energy barrier. The similarities in the re-orientation temperatures of PtH2 and V2 allows us to conclude that the barrier for the PtH2 re-orientation would be close to or above 1 eV. If the stress is applied at temperatures where the complex re-orientates and then the sample is cooled quickly to the measurement temperature the complexes do indeed take on a preferential direction in respect to the stress. This experimental procedure has been applied for all three orientations of samples investigated and the effect of the alignment has been observed as a change in the peak amplitude ratios in respect to the ones observed for the non-aligned defects. It has been found that the alignment procedure for all stress directions makes the stress-split Laplace DLTS peak observed at higher emission rates decreases in favour of the one observed at lower emission rates. For the bias on conditions this is opposite to the tendency in the alignment effect observed for the VO complex. Due to the fact that for the /1 1 0S direction the two configurations observed in the spectra at lower emission rates are not resolved one cannot conclude which of them gains in amplitude when the one at higher emission rates decreases. In summary, we demonstrated that a use of the Laplace DLTS combined with the uniaxial stress technique allowed us to investigate in details the structure and electrical properties of the platinumand hydrogen-related complex PtH2. These results allow to relate the defect electronic level to the results of other spectroscopic studies performed with the electron resonance and far-infrared absorption measurements. We have correlated the sample processing procedure with the energy level of the PtH2 complex at Ec 0:159 eV. The
observed stress-induced peak splitting pattern confirms the orthorhombic-I C2v symmetry of this platinum- and hydrogen-related complex. The studies of the complex re-orientation and alignment effect allowed us to conclude that this complex does not reconfigure at temperatures below room temperature for bias on and off conditions.
Acknowledgements Discussions with B. Hourahine, R. Jones, and V.P. Markevich are acknowledged. This work has been supported in part by the State Committee for Scientific Research Grant No. 4T11B02123 in Poland, the Danish National Research Foundation through the Aarhus Center for Atomic Physics (ACAP) and in the UK by the Engineering and Physical Science Research Council.
References [1] P.T. Huy, C.A.J. Ammerlaan, Physica B 302–303 (2001) 233. [2] T. Mchedlidze, N. Fukata, M. Suezawa, Jpn. J. Appl. Phys. 41 (2002) L967. [3] J.-U. Sachse, J. Weber, E.O. Sveinbjornsson, Phys. Rev. B 60 (1999) 1474. [4] J. Weber, S. Knack, J.-U. Sachse, Physica B 273–274 (1999) 429. [5] N. Yarykin, J.-U. Sachse, J. Weber, H. Lemke, Phys. Rev. B 59 (1999) 5551. [6] S. Knack, J. Weber, H. Lemke, H. Riemann, Physica B 308–310 (2001) 404. [7] O.V. Feklisova, A.L. Parakhonsky, E.B. Yakimov, J. Weber, Mater. Sci. Eng. 71 (2000) 268. [8] E.O. Sveinbjornsson, O. Engstrom, Phys. Rev. B 52 (1995) 4884. [9] P.M. Williams, G.D. Watkins, S. Uftring, M. Stavola, Phys. Rev. Lett. 70 (1993) 3816. [10] M.J. Evans, M. Stavola, M.G. Weinstein, S.J. Uftring, Mater. Sci. Eng. B 58 (1999) 118. [11] M.J. Evans, Mater. Sci. Eng. 58 (1999) 118. [12] S.J. Uftring, M. Stavola, P.M. Williams, G.D. Watkins, Phys. Rev. B 51 (1995) 9612. [13] M. Hohne, et al., Phys. Rev. B 49 (1994) 13423. [14] M.G. Weinstein, et al., Phys. Rev. B 65 (2001) 035206. [15] K. Fukuda, et al., Physica B 308–310 (2001) 240. [16] L. Dobaczewski, P. Kaczor, I.D. Hawkins, A.R. Peaker, J. Appl. Phys. 76 (1994) 194.
ARTICLE IN PRESS V. Kolkovski et al. / Physica B 340–342 (2003) 677–681 [17] L. Dobaczewski, O. Andersen, L. Rubaldo, K. Goscinski, V.P. Markevich, A.R. Peaker, K. Bonde Nielsen, Phys. Rev. B 67 (2003) 195204. [18] L. Dobaczewski, K. Goscinski, Z.R. Zytkiewicz, K. Bonde Nielsen, L. Rubaldo, O. Andersen, A.R. Peaker, Phys. Rev. B 65 (2002) 113203. [19] K. Fukuda, Y. Kamiura, Y. Yamashita, T. Ishiyama, Jpn. J. Appl. Phys. 6700 (2001) 40;
681
O. Andersen, A.R. Peaker, L. Dobaczewski, K. Bonde Nielsen, B. Hourahine, R. Jones, P.R. Briddon, S. Oberg, Phys. Rev. B 66 (2002) 235205. [20] J. Coutinho, O. Andersen, L. Dobaczewski, K. Bonde . Nielsen, A.R. Peaker, R. Jones, S. Oberg, P.R. Briddon, unpublished.
Physica B 340–342 (2003) 677–681
Piezospectroscopic analysis of the Pt–H2 complex in silicon V. Kolkovskia,*, O. Andersenb, L. Dobaczewskia, A.R. Peakerb, K. Bonde Nielsenc a
Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland b Centre for Electronic Materials, Devices and Nanostructures, UMIST, Manchester, UK c Institute of Physics and Astronomy, University of Aarhus, Aarhus, Denmark
Abstract In this study the use of the high-resolution Laplace DLTS combined with uniaxial stress has allowed us to investigate in detail the structure and electrical properties of the platinum–hydrogen-related complex PtH2. We correlate the defect electronic level with the results of other spectroscopic studies performed with electron paramagnetic resonance and farinfrared absorption measurements. The observed stress-induced peak splitting pattern confirms the orthorhombic-IC2v symmetry of the complex. The re-orientation process of the defect can be observed at temperatures higher than the room temperature for all bias conditions. r 2003 Elsevier B.V. All rights reserved. PACS: 61.72.Ji; 71.55.Cn; 71.70.Ft Keywords: Platinum–hydrogen complex; Laplace DLTS; Piezospectroscopy
Defects and complexes related to transition metals (TM) in silicon still remain an important topic for research. They act as an effective tool for minority carrier lifetime control in semiconductor power devices. Hydrogen is known to be one of the most common unintentional impurities in silicon. It interacts with TM and can result in either passivation of the associated deep levels, i.e. a disappearance of the electrical activity of the TM in the crystal (in early studies only complete passivation electrically active complexes by hydrogen was reported), or in the formation of electrically active TM–hydrogen complexes. As a result of this, the effect of hydrogen on the electrical properties of TM in silicon, especially *Corresponding author. Fax: +48-847-5223. E-mail address: [email protected] (V. Kolkovski).
the formation of electrically active complexes, has been studied by means of electron paramagnetic resonance (EPR) [1,2], deep level transient spectroscopy (DLTS) combined with depth-profile or annealing studies [3–8] and local vibrational mode (LVM) spectroscopy [9–11]. These techniques have provided valuable information about the position of the TM–H levels in the band gap, their electron and hole capture cross sections, the numbers of hydrogen atoms involved as well as their positions within the structure of the defects. The interaction of hydrogen and platinum in silicon has been the subject of several reports [12–15]. DLTS measurements combined with depth-profiling and annealing studies showed that platinum forms several complexes after hydrogenation by wet-chemical etching. Four platinum–hydrogen related deep levels have been
0921-4526/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2003.09.164
ARTICLE IN PRESS V. Kolkovski et al. / Physica B 340–342 (2003) 677–681
identified E(90), E(250) in n-type silicon and H(150), H(210) in p-type silicon. It has been proposed [3,14] that the origin of another DLTS peak, E(90), is a PtH2 centre, however, there was no direct evidence connecting this peak with the PtH2 complex which was observed by EPR. Fukuda et al. [15] resolved this issue by applying conventional DLTS combined with uniaxial stress. They demonstrated that the stress splitting is consistent with orthorhombic-I symmetry of PtH2 in agreement with the results of EPR, LVM and theoretical calculations. However, because a defect re-orientation process is observed in Ref. [15] at temperatures about 90 K it has been concluded that the alignment process for the PtH2 complex is even more efficient than for the case of the vacancy–oxygen (VO) pair. In our study we correlate the sample processing procedure with energy level corresponding to the PtH2 complex. Using high-resolution Laplace DLTS (LDLTS) [16] combined with uniaxial stress we confirm that the structure of this defect is orthorhombic. The influence of uniaxial stress on the ionisation process has been studied for different orientations of the stress in relation to the crystallographic directions and it has been concluded that the effect of stress on the process is rather weak in comparison to that already observed for the case of VO [17], the divacancy (V2) [18], and the carbon–hydrogen pair [19] in the n-type silicon. We also have observed that in our samples the defect re-orientation process apparent as a stress-induced alignment effect only occurs at temperatures higher than 300 K. This is the case for both charge states of the PtH2 centre and, in this respect, does not agree with the findings reported in Ref. [15]. The samples for this study have been prepared from the (1 0 0)-oriented phosphorous-doped floatzone grown silicon with a resistivity of 21–23 Ocm. The samples were cut into 7 2 1 mm3 bars with the long dimension parallel to one of the major crystallographic directions /1 0 0S, /1 1 0S or /1 1 1S. A thin platinum layer was evaporated onto one side of silicon wafer and diffused in at B820 C for 2 h in a nitrogen atmosphere. The samples were etched for 2 min in CP4A solution in order to introduce hydrogen and eliminate the
high surface concentration of platinum resulting from the U-shape of the in-diffused TM. Additional hydrogen has been introduced during a 30 min soak in a solution of nitric (70%) and hydrofluoric (48%) acids in a 10:1 ratio. The Schottky diodes were formed by vacuum evaporation of gold on the polished and etched side of the wafer. An eutectic InGa alloy was rubbed onto the back side of the samples to fabricate an Ohmic contact. A series of test samples made on randomly oriented pieces of the same wafers according to the procedure described has also been produced for calibration of the platinum and hydrogen diffusion process. Fig. 1 shows typical conventional DLTS spectra for three test samples prepared from the same crystal. The spectra depicted in Fig. 1 were recorded directly after the wet-chemical etching. Three dominant DLTS peaks are observed at 100, 120 and 270 K. These peaks are detected in all platinum and hydrogen diffused n-type samples. The peak at 120 K is a well-known acceptor state of the isolated substitutional platinum atom. Two other peaks at 100 and 270 K have been assigned as related to PtH2 and PtH, respectively [3]. The introduction of atomic hydrogen via the
Si FZ Pt-diffusion 30 mins and etching DLTS signal (arb. units)
678
PtH
Pt(-/0) 850 C 820 C 775 C
PtH 2
100
150
200
250
300
Temperature (K) Fig. 1. The conventional DLTS spectra of Pt-doped n-type float zone Si after a 30 min Pt-diffusion at different diffusion temperatures followed the wet-chemical etching which introduces hydrogen.
ARTICLE IN PRESS V. Kolkovski et al. / Physica B 340–342 (2003) 677–681
Si: PtH2 T=90K Laplace DLTS amplitude (arb. units)
wet-chemical etching procedure has the disadvantage that the amount of hydrogen introduced into the crystal cannot be monitored precisely. However, this procedure allows the concentration of hydrogen to be reproduced when the etching procedure is carefully repeated. As seen in the figure, an increase of the platinum diffusion temperature results in an increase of the platinum concentration while the wet-etching procedure introduces in each case a similar amount of hydrogen. As a result, the ratio between the PtH2 and other peaks, i.e. Pt and PtH, decreases showing that hydrogen has a tendency to decorate the platinum atoms. No deep levels have been detected using either Laplace or conventional DLTS spectra in reference samples not diffused with platinum. The electronic level corresponding to the PtH2 complex and related to the peak at 100 K is characterised by the capture cross section sn ¼ 9 1016 cm2 (evaluated from the filling pulse method) and the activation energy of the emission Et ¼ Ec 0:159 eV. These values agree, within reasonable error limits, with the ones reported in Ref. [15]. As mentioned above, the structure of the stable PtH2 complex established by EPR has the orthorhombic-I C2v symmetry. Thus, the defect has two non-equivalent orientations of degeneracy 2 and 4 for stress along the /1 0 0S direction, three non-equivalent orientations of degeneracy 1, 4 and 1 for stress along the /1 1 0S direction, and finally two non-equivalent orientations of degeneracy 3 and 3 for stress along /1 1 1S direction. Fig. 2 shows the 90 K Laplace DLTS spectra of PtH2 obtained at zero stress and under uniaxial stress along the three major crystallographic directions. For each stress-direction, the zero-stress peak splits into two well-resolved peaks. The amplitudes of the split lines sum up to the amplitude of the zero-stress peak. The experimental amplitude ratios of the individual peaks in Fig. 2 agree to within 10% of the ratios expected for an orthorhombic-I centre, i.e. 2:4 for the /1 0 0S stress direction, (1+4):1 for the /1 1 0S stress direction (note a broadened larger peak, which could be a result of the unresolved additional splitting) and 3:3 for the /1 1 1S stress direction.
679
<111> 0.20GPa
<110> 0.23GPa
<100> 0.15GPa
0GPa
1
10
Emission rate
100
(s-1)
Fig. 2. Laplace DLTS spectra of PtH2 obtained at zero stress and under uniaxial stress along the three major crystallographic directions, /1 0 0S, /1 1 0S and /1 1 1S. The splitting pattern confirms the orthorhombic-I symmetry of the PtH2 complex.
According to our observations, the PtH2 complex only starts to re-orientate at temperatures above 300 K. When the sample bias is applied (and consequently adding an electron to the PtH2 centre) this re-orientation temperature needs to be a little higher than the one for the bias off conditions. This is in agreement to a general trend observed, for example, in the vacancy–oxygen [17] and the vacancy–oxygen–hydrogen [20] complexes, where it has been found that the reorientation barrier increases when there are more electrons captured by a complex. The re-orientation barriers of vacancy-involving orthorhombic (VO) and pseudo-orthorhombic (VOH) complexes are 0.38 and 0.56 eV, respectively. In consequence these defects start to re-orientate (in a time scale of minutes) at temperatures around 100 and 200 K for VO and VOH, respectively. In the PtH2 complex no vacancies are involved and so in principle it might be expected that the lack of
ARTICLE IN PRESS 680
V. Kolkovski et al. / Physica B 340–342 (2003) 677–681
empty volume in the unit cell could make the reorientation process much more difficult. As a result, the re-orientation barrier would be expected to be much higher than the one observed in the former two cases. On the other hand, it has been already observed that the divacancy in silicon only starts to re-orientate at temperatures above 350 K and in this case this process is thought to be identical with the long-range diffusion of the complex [18]. The diffusion of the divacancy is governed by a 1.3 eV energy barrier. The similarities in the re-orientation temperatures of PtH2 and V2 allows us to conclude that the barrier for the PtH2 re-orientation would be close to or above 1 eV. If the stress is applied at temperatures where the complex re-orientates and then the sample is cooled quickly to the measurement temperature the complexes do indeed take on a preferential direction in respect to the stress. This experimental procedure has been applied for all three orientations of samples investigated and the effect of the alignment has been observed as a change in the peak amplitude ratios in respect to the ones observed for the non-aligned defects. It has been found that the alignment procedure for all stress directions makes the stress-split Laplace DLTS peak observed at higher emission rates decreases in favour of the one observed at lower emission rates. For the bias on conditions this is opposite to the tendency in the alignment effect observed for the VO complex. Due to the fact that for the /1 1 0S direction the two configurations observed in the spectra at lower emission rates are not resolved one cannot conclude which of them gains in amplitude when the one at higher emission rates decreases. In summary, we demonstrated that a use of the Laplace DLTS combined with the uniaxial stress technique allowed us to investigate in details the structure and electrical properties of the platinumand hydrogen-related complex PtH2. These results allow to relate the defect electronic level to the results of other spectroscopic studies performed with the electron resonance and far-infrared absorption measurements. We have correlated the sample processing procedure with the energy level of the PtH2 complex at Ec 0:159 eV. The
observed stress-induced peak splitting pattern confirms the orthorhombic-I C2v symmetry of this platinum- and hydrogen-related complex. The studies of the complex re-orientation and alignment effect allowed us to conclude that this complex does not reconfigure at temperatures below room temperature for bias on and off conditions.
Acknowledgements Discussions with B. Hourahine, R. Jones, and V.P. Markevich are acknowledged. This work has been supported in part by the State Committee for Scientific Research Grant No. 4T11B02123 in Poland, the Danish National Research Foundation through the Aarhus Center for Atomic Physics (ACAP) and in the UK by the Engineering and Physical Science Research Council.
References [1] P.T. Huy, C.A.J. Ammerlaan, Physica B 302–303 (2001) 233. [2] T. Mchedlidze, N. Fukata, M. Suezawa, Jpn. J. Appl. Phys. 41 (2002) L967. [3] J.-U. Sachse, J. Weber, E.O. Sveinbjornsson, Phys. Rev. B 60 (1999) 1474. [4] J. Weber, S. Knack, J.-U. Sachse, Physica B 273–274 (1999) 429. [5] N. Yarykin, J.-U. Sachse, J. Weber, H. Lemke, Phys. Rev. B 59 (1999) 5551. [6] S. Knack, J. Weber, H. Lemke, H. Riemann, Physica B 308–310 (2001) 404. [7] O.V. Feklisova, A.L. Parakhonsky, E.B. Yakimov, J. Weber, Mater. Sci. Eng. 71 (2000) 268. [8] E.O. Sveinbjornsson, O. Engstrom, Phys. Rev. B 52 (1995) 4884. [9] P.M. Williams, G.D. Watkins, S. Uftring, M. Stavola, Phys. Rev. Lett. 70 (1993) 3816. [10] M.J. Evans, M. Stavola, M.G. Weinstein, S.J. Uftring, Mater. Sci. Eng. B 58 (1999) 118. [11] M.J. Evans, Mater. Sci. Eng. 58 (1999) 118. [12] S.J. Uftring, M. Stavola, P.M. Williams, G.D. Watkins, Phys. Rev. B 51 (1995) 9612. [13] M. Hohne, et al., Phys. Rev. B 49 (1994) 13423. [14] M.G. Weinstein, et al., Phys. Rev. B 65 (2001) 035206. [15] K. Fukuda, et al., Physica B 308–310 (2001) 240. [16] L. Dobaczewski, P. Kaczor, I.D. Hawkins, A.R. Peaker, J. Appl. Phys. 76 (1994) 194.
ARTICLE IN PRESS V. Kolkovski et al. / Physica B 340–342 (2003) 677–681 [17] L. Dobaczewski, O. Andersen, L. Rubaldo, K. Goscinski, V.P. Markevich, A.R. Peaker, K. Bonde Nielsen, Phys. Rev. B 67 (2003) 195204. [18] L. Dobaczewski, K. Goscinski, Z.R. Zytkiewicz, K. Bonde Nielsen, L. Rubaldo, O. Andersen, A.R. Peaker, Phys. Rev. B 65 (2002) 113203. [19] K. Fukuda, Y. Kamiura, Y. Yamashita, T. Ishiyama, Jpn. J. Appl. Phys. 6700 (2001) 40;
681
O. Andersen, A.R. Peaker, L. Dobaczewski, K. Bonde Nielsen, B. Hourahine, R. Jones, P.R. Briddon, S. Oberg, Phys. Rev. B 66 (2002) 235205. [20] J. Coutinho, O. Andersen, L. Dobaczewski, K. Bonde . Nielsen, A.R. Peaker, R. Jones, S. Oberg, P.R. Briddon, unpublished.