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Determination of lattice displacements in Se implanted InP by RBS and PIXE channeling experiments
Nuclear Instruments and Methods in Physics Research B 161±163 (2000) 515±519
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Determination of lattice displacements in Se implanted InP by RBS and PIXE channeling experiments F. Schrempel *, T. Opfermann, E. Wendler, W. Wesch Friedrich-Schiller-Universit at Jena, Institut f ur Festk orperphysik, Max-Wien-Platz 1, D-07743 Jena, Germany
Abstract á1 0 0ñ InP single crystals were implanted with 600 keV Se at the critical temperature of 423 K with ion ¯uences ranging from 1013 to 1015 cmÿ2 . The damaging of the In and P sublattices and the lattice location of the Se atoms have been studied by RBS and PIXE angular scan curves along the á1 0 0ñ and á1 1 0ñ directions. The critical angles and minimum yields have been extracted for each measurement. An attempt is made to determine the displacement distance of the constituent atoms from their lattice site. Ó 2000 Elsevier Science B.V. All rights reserved. PACS: 61.18.Bn; 61.72.Dd; 61.72.Ji; 61.80.Jh Keywords: III/V compounds; InP; Ion implantation; RBS; PIXE; Channeling
1. Introduction In ion implanted compound semiconductors under certain conditions high concentrations of displaced lattice atoms are detected [1]. It was found that the primary collision cascades are not stable and the resulting damage arises from defect rearrangement and annealing, if the implantation is carried out near a critical temperature [2±5]. As a consequence of these processes it may be possible that stable defect con®gurations are formed, in which preferentially one of the constituent atoms
* Corresponding author. Tel.: +49-3641-947-318; fax: +493641-947-302. E-mail address: [email protected] (F. Schrempel).
is involved. The separate signals of characteristic X-rays allow to study the single constituents of compound semiconductors. In combination with channeling experiments it can be estimated whether one of the two sublattices is more damaged than the other one. In a previous work on weakly damaged GaAs layers we demonstrated that the root-mean-square (rms) thermal vibration amplitudes calculated from the half-widths of RBS and PIXE angular scans re¯ect the ¯uence dependent changes of the concentration and the displacement distance of displaced lattice atoms [5]. In the case of GaAs there are indications that the As sublattice is slightly more damaged than the Ga sublattice. In the present paper we analyse weakly damaged InP layers, where the mass difference between the constituent lattice atoms is very large in contrast to GaAs. Therefore one
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 7 7 9 - X
516
F. Schrempel et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 515±519
expects a stronger dierence in the damage of the two sublattices compared to GaAs. Additionally, information about preferred displacements can be obtained by angular scans in contrast to simple channelling measurements, because such defects are visible as kinks in the dip, directly. For GaAs we found weak kinks only for the As dips, supporting the assumption that the As sublattice is more damaged than the Ga sublattice. In the present experiments we implanted Se ions into InP, because Se is an often used ion species to produce n-type activation in InP and results have been published to enable a comparison with our previous experiments [3,4]. 2. Experimental methods To obtain weakly damaged layers over a wide ¯uence range á1 0 0ñ oriented InP wafers were implanted with 600 keV Se ions at a temperature of 150°C, i.e. around the critical temperature. The ion ¯uence NI was varied between 2 1013 and 3 1015 cmÿ2 . The implantation was carried out 7° o the axis in order to avoid channeling eects, and the beam current was kept below 0.2 lAcmÿ2 . The damaged layer extends from the surfaces to a depth of 600 nm and the maximum is reached at a depth of about 300 nm [3,4]. For analysis a conventional channeling setup on the 3 MV tandetron accelerator JULIA at Jena was used. The spread of the collimated beam was below 0.02°. Angular scan curves of the RBS and PIXE signals were measured simultaneously using 1.4 MeV He ions across the á1 0 0ñ and the á1 1 0ñ axis by tilting the samples at 0.1°/0.05° increments. All measurements were carried out at room temperature and the beam current was kept below 10 nA with a spot size of about 1.2 mm in diameter. The total beam ¯uences ranged from 20 to 40 lC for a single angular scan to avoid damage by the ions during the measurement. Backscattered ions were detected by a surface barrier detector at a backscattering angle of 170°. Characteristic X-rays were measured by a Si(Li) detector placed at 145° with respect to the beam direction. The exit angles with respect to the surface normal of the sample were 35° and 80° for the á1 0 0ñ and á1 1 0ñ angular
measurements, respectively. In order to ensure a good reproducibility of the angular scans the tilting plane was rotated 15° with respect to the (0 1 0) plane in the case of the á1 0 0ñ scans. For the á1 1 0ñ scans it was tilted parallel to the (1 0 1) plane.
3. Results and discussion The backscattering spectra in Fig. 1 are mainly characterised by dechanneling of the He ions, indicating the existence of point defects and point defect complexes. No backscattering peak occurs up to the highest ion ¯uence NI 3 1015 cmÿ2 (not shown). Examples for angular scans of perfect and of implanted InP crystals are given in Figs. 2 and 3 for á1 0 0ñ and á1 1 0ñ scans, respectively. The scans of the implanted samples look similar for all ion ¯uences, but vary slightly in minimum yields vmin and angular half-widths W1=2 . The RBS angular scan curve of the In part has been obtained by integration of the backscattering yields within the damaged region (see dashed lines in Fig. 2). The PIXE curves are taken from the In±L, P±K and the Se±K X-ray signals. The measurement errors are in the order of the symbol sizes except for the Se curves, where the errors amount between 5% and 10%, because of the small concentration of Se atoms. In the á1 0 0ñ and á1 1 0ñ directions there are
Fig. 1. Energy spectra of 1.4 MeV He ions backscattered on 600 keV Se implanted InP for dierent ion ¯uences.
F. Schrempel et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 515±519
Fig. 2. PIXE á1 0 0ñ angular scans of In±L and P±K lines for perfect InP and additional scans of Se±K lines for InP implanted with 600 keV Se ions (NI 4 1014 cmÿ2 ). The dashed line represents the In part of the RBS á1 0 0ñ scan obtained by integrating within the damaged region.
517
sites corresponding to the results of location studies by Xiao et al. [6]. The fact that Se is incorporated preferentially into substitutional sites of one of the sublattices is also con®rmed by the asymmetric shoulder appearing for the Se á1 1 0ñ scan at positive tilt angles [7,8]. No kinks in the scan curves appear, which indicates the absence of preferable distances of displaced atoms. A summary of the dierences in minimum yield Dvmin vmin;implanted ÿ vmin;perfect as a function of ion ¯uence is given in Fig. 4. The Dvmin values slightly increase with the ion ¯uence re¯ecting the increasing damage. The relative large ¯uctuations are typical for implantations around the critical temperature. As can be seen the Dvmin values are remarkably larger for P than for In and the difference appears to be stronger for the á1 0 0ñ than for the á1 1 0ñ measurements. This indicates that
Fig. 3. PIXE á1 1 0ñ angular scans similar to Fig. 2, but with a higher ion ¯uence (NI 1 1015 cmÿ2 ).
separate atomic rows for In and P. Rows of atoms with low atomic number Z have narrower angular pro®les than rows of heavier atoms, which is indeed obtained for P (Z 15) and In (Z 49). A foreign atom with low concentration will then have a pro®le similar to that of the major constituent of the row where it resides. Despite the large errors for Se for both directions the Se angular distributions agree with the P distributions clearly. Therefore, Se must occupy regular P lattice
Fig. 4. Dierence in minimum yield Dvmin versus the ion ¯uence NI of 600 keV Se implanted InP. The crosses are the Dvmin obtained from the In part of RBS measurements. The other symbols represent the values extracted from In±L and P±K X-ray measurements corresponding to the symbols in Figs. 2 and 3.
518
F. Schrempel et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 515±519
axial channeling regime. The angular half-widths estimated from the PIXE curves allow the calculation of rms thermal vibration amplitudes u1 in the framework of LindhardÕs continuum model [10] using the equations developed by Barett [11]. In the case of a perfect crystal the angular halfwidth is given by [11]
the P sublattice is considerably more damaged than the In sublattice verifying that Se is incorporated into P sites. Thereby we do not ignore that the dierent X-ray absorption for In and P in¯uence the minimum yields. In the case of the á1 0 0ñ measurements 41% of the In signal and 56% of the P signal come from the damaged layer and the other parts come from the underlying substrate. Taking this into account the dierences between the Dvmin of In and P will be still larger than the values shown in Fig. 4. The In X-rays come from larger depths than the P X-rays, i.e. from regions of higher vmin if pure dechanneling is observed. Moreover the Dvmin of In are almost the same for both axes or slightly larger for the á1 1 0ñ than for the á1 0 0ñ axis indicating stronger damage, which indeed is expected for implantations close to the á1 0 0ñ axis. In the case of the P sublattice the opposite behaviour is observed. Possibly this can be explained by the formation of defect complexes with substitutional P atoms, which are preferentially oriented perpendicularly to the á1 0 0ñ axis. As can be seen in Fig. 1, the useful depth for the ions backscattered by In atoms is about 500 nm, but the transition from planar to pure axial channeling occurs in the deeper region [5,9]. The in¯uence of planar channeling near the surface leads to an increase of W1=2 and no extrapolation of the angular half-width W1=2 for the RBS angular scan curves to the surface can be performed (see [5]). In contrast, the X-rays are integrally measured with respect to the depth from the surfaces down to about 3 lm where we can assume pure
W1=2
1:2u1 0:8R W1 ; aTF
1
where aTF is the Thomas±Fermi radius and W1 is LindhardÕs critical angle for channeling [10]. The function R has been tabulated by Barett and W1 is given by r 2Z1 Z2 e2 ; W1 Ed
2
where Z1 and Z2 are the atomic numbers of the projectile and the target atom, E is the incidence energy of the projectile, e is the electronic charge and d is the atomic spacing along the row. Using both formulas given above and W1=2 for the perfect crystal estimated from the á1 0 0ñ scans we obtain and u1 0:11 A for In and P, reu1 0:09 A spectively (see Table 1). These values are in good agreement to DebyeÕs theory using a Debye temperature of 321 K for InP, which gives rms thermal for In and 0.166 A vibration amplitudes of 0.086 A for P. In the case of implanted samples u1 in Eq. (1) can be regarded as a mean value u1 which is determined by both the rms thermal vibration
Table 1 Angular half-width W1=2 , root-mean-square displacement u1 and mean displacement distance ra for In and P obtained by the measurement of á1 0 0ñ angular PIXE scans of 600 keV implanted InP Ion ¯uence NI (cmÿ2 )
0 2 1013 1 1014 4 1014 1 1015
Angular half-width W1=2 (°)
Root-mean-square displacement u1 (A)
Mean displacement distance ra (A)
In
P
In
P
In
P
0.55 0.53 0.55 0.51 0.51
0.39 0.38 0.38 0.37 0.35
0.090 0.094 0.090 0.098 0.098
0.110 0.112 0.112 0.119 0.133
± 0.10 0.09 0.14 0.14
± 0.12 0.12 0.16 0.23
F. Schrempel et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 515±519
amplitude u1 of the atoms not displaced and the mean displacement distance ra of the displaced lattice atoms caused by the implantation induced damage. With the corresponding mean values of the concentrations of displaced lattice atoms ndat one obtains r 1 ÿ ndat u21 ndat ra2 : 3 u1 The measured angular half-widths W1=2 and the u1 values calculated by Eq. (1) are given in Table 1. In [3±5] it has been shown that for implantations with low ion ¯uences above the critical temperature isolated point defects cause dominant lattice distortions, which results in large ndat values. At higher ¯uences the lattice distortion is reduced due to higher defect concentrations. Therefore, the mean concentration of displaced atoms ndat decreases and remains almost constant until amorphisation occurs. With ndat 0:33 for NI 21013 cmÿ2 and ndat 0:14 for NI > 2 1013 cmÿ2 taken from [4] the mean displacement distances ra were calculated by Eq. (3). The results are summarised in Table 1, and the following can be seen. The values represent the damage increasing with increasing ion ¯uence. The mean displacement distances ra obtained from the angular PIXE scans are lower than the values obtained by temperature for low and dependent RBS measurements (0.2 A 0.4±0.5 A for the higher ion ¯uences [4]). This is due to the eect that the analysed depth is much larger than the thickness of the damaged layer. If it is taken into account that only almost 50% of the X-ray signals come from the damaged layer both results are in agreement.
519
4. Summary Weakly damaged ion implanted InP layers have been studied by the measurement of RBS and PIXE angular scans. The results are: (i) Nearly all implanted Se atoms occupy regular lattice sites of the P sublattice. (ii) The P sublattice is more strongly damaged than the In sublattice. (iii) We expect the formation of defect complexes with substitutional P atoms, which are preferentially oriented perpendicularly to the á1 0 0ñ axis. (iv) The mean displacement distances estimated by the angular half scans almost agree with the values obtained by temperature dependent RBS measurements.
References [1] W. Wesch, Mater. Res. Soc. Symp. Proc. 300 (1993) 297. [2] E. Wendler, W. Wesch, Nucl. Instr. and Meth. B 73 (1993) 489. [3] E. Wendler, T. Opfermann, P.I. Gaiduk, J. Appl. Phys. 82 (11) (1997) 5965. [4] T. Opfermann, Diploma thesis, Friedrich-Schiller-Universit at Jena, 1995. [5] E. Wendler, F. Schrempel, P. M uller, K. G artner, W. Wesch, Nucl. Instr. and Meth. B 118 (1996) 367. [6] Q.F. Xiao, S. Hashimoto, W.M. Gibson, S.J. Pearton, Nucl. Instr. and Meth. B 45 (1990) 464. [7] A. Bontemps, J. Fontenille, A. GuivarcÕh, Phys. Lett. A 55 (1976) 373. [8] J.U. Andersen, N.G. Chechenin, Z.Z. Hua, Appl. Phys. Lett. 39 (1981) 758. [9] A. Desalvo, R. Rosa, Phys. Rev. B 9 (11) (1974) 4605. [10] J. Lindhard, K. Dan. Vidensk. Selskab. Mat.-Fys. Medd 34 (14) (1965). [11] J.H. Barett, Phys. Rev. B 3 (1971) 1527.
www.elsevier.nl/locate/nimb
Determination of lattice displacements in Se implanted InP by RBS and PIXE channeling experiments F. Schrempel *, T. Opfermann, E. Wendler, W. Wesch Friedrich-Schiller-Universit at Jena, Institut f ur Festk orperphysik, Max-Wien-Platz 1, D-07743 Jena, Germany
Abstract á1 0 0ñ InP single crystals were implanted with 600 keV Se at the critical temperature of 423 K with ion ¯uences ranging from 1013 to 1015 cmÿ2 . The damaging of the In and P sublattices and the lattice location of the Se atoms have been studied by RBS and PIXE angular scan curves along the á1 0 0ñ and á1 1 0ñ directions. The critical angles and minimum yields have been extracted for each measurement. An attempt is made to determine the displacement distance of the constituent atoms from their lattice site. Ó 2000 Elsevier Science B.V. All rights reserved. PACS: 61.18.Bn; 61.72.Dd; 61.72.Ji; 61.80.Jh Keywords: III/V compounds; InP; Ion implantation; RBS; PIXE; Channeling
1. Introduction In ion implanted compound semiconductors under certain conditions high concentrations of displaced lattice atoms are detected [1]. It was found that the primary collision cascades are not stable and the resulting damage arises from defect rearrangement and annealing, if the implantation is carried out near a critical temperature [2±5]. As a consequence of these processes it may be possible that stable defect con®gurations are formed, in which preferentially one of the constituent atoms
* Corresponding author. Tel.: +49-3641-947-318; fax: +493641-947-302. E-mail address: [email protected] (F. Schrempel).
is involved. The separate signals of characteristic X-rays allow to study the single constituents of compound semiconductors. In combination with channeling experiments it can be estimated whether one of the two sublattices is more damaged than the other one. In a previous work on weakly damaged GaAs layers we demonstrated that the root-mean-square (rms) thermal vibration amplitudes calculated from the half-widths of RBS and PIXE angular scans re¯ect the ¯uence dependent changes of the concentration and the displacement distance of displaced lattice atoms [5]. In the case of GaAs there are indications that the As sublattice is slightly more damaged than the Ga sublattice. In the present paper we analyse weakly damaged InP layers, where the mass difference between the constituent lattice atoms is very large in contrast to GaAs. Therefore one
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 7 7 9 - X
516
F. Schrempel et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 515±519
expects a stronger dierence in the damage of the two sublattices compared to GaAs. Additionally, information about preferred displacements can be obtained by angular scans in contrast to simple channelling measurements, because such defects are visible as kinks in the dip, directly. For GaAs we found weak kinks only for the As dips, supporting the assumption that the As sublattice is more damaged than the Ga sublattice. In the present experiments we implanted Se ions into InP, because Se is an often used ion species to produce n-type activation in InP and results have been published to enable a comparison with our previous experiments [3,4]. 2. Experimental methods To obtain weakly damaged layers over a wide ¯uence range á1 0 0ñ oriented InP wafers were implanted with 600 keV Se ions at a temperature of 150°C, i.e. around the critical temperature. The ion ¯uence NI was varied between 2 1013 and 3 1015 cmÿ2 . The implantation was carried out 7° o the axis in order to avoid channeling eects, and the beam current was kept below 0.2 lAcmÿ2 . The damaged layer extends from the surfaces to a depth of 600 nm and the maximum is reached at a depth of about 300 nm [3,4]. For analysis a conventional channeling setup on the 3 MV tandetron accelerator JULIA at Jena was used. The spread of the collimated beam was below 0.02°. Angular scan curves of the RBS and PIXE signals were measured simultaneously using 1.4 MeV He ions across the á1 0 0ñ and the á1 1 0ñ axis by tilting the samples at 0.1°/0.05° increments. All measurements were carried out at room temperature and the beam current was kept below 10 nA with a spot size of about 1.2 mm in diameter. The total beam ¯uences ranged from 20 to 40 lC for a single angular scan to avoid damage by the ions during the measurement. Backscattered ions were detected by a surface barrier detector at a backscattering angle of 170°. Characteristic X-rays were measured by a Si(Li) detector placed at 145° with respect to the beam direction. The exit angles with respect to the surface normal of the sample were 35° and 80° for the á1 0 0ñ and á1 1 0ñ angular
measurements, respectively. In order to ensure a good reproducibility of the angular scans the tilting plane was rotated 15° with respect to the (0 1 0) plane in the case of the á1 0 0ñ scans. For the á1 1 0ñ scans it was tilted parallel to the (1 0 1) plane.
3. Results and discussion The backscattering spectra in Fig. 1 are mainly characterised by dechanneling of the He ions, indicating the existence of point defects and point defect complexes. No backscattering peak occurs up to the highest ion ¯uence NI 3 1015 cmÿ2 (not shown). Examples for angular scans of perfect and of implanted InP crystals are given in Figs. 2 and 3 for á1 0 0ñ and á1 1 0ñ scans, respectively. The scans of the implanted samples look similar for all ion ¯uences, but vary slightly in minimum yields vmin and angular half-widths W1=2 . The RBS angular scan curve of the In part has been obtained by integration of the backscattering yields within the damaged region (see dashed lines in Fig. 2). The PIXE curves are taken from the In±L, P±K and the Se±K X-ray signals. The measurement errors are in the order of the symbol sizes except for the Se curves, where the errors amount between 5% and 10%, because of the small concentration of Se atoms. In the á1 0 0ñ and á1 1 0ñ directions there are
Fig. 1. Energy spectra of 1.4 MeV He ions backscattered on 600 keV Se implanted InP for dierent ion ¯uences.
F. Schrempel et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 515±519
Fig. 2. PIXE á1 0 0ñ angular scans of In±L and P±K lines for perfect InP and additional scans of Se±K lines for InP implanted with 600 keV Se ions (NI 4 1014 cmÿ2 ). The dashed line represents the In part of the RBS á1 0 0ñ scan obtained by integrating within the damaged region.
517
sites corresponding to the results of location studies by Xiao et al. [6]. The fact that Se is incorporated preferentially into substitutional sites of one of the sublattices is also con®rmed by the asymmetric shoulder appearing for the Se á1 1 0ñ scan at positive tilt angles [7,8]. No kinks in the scan curves appear, which indicates the absence of preferable distances of displaced atoms. A summary of the dierences in minimum yield Dvmin vmin;implanted ÿ vmin;perfect as a function of ion ¯uence is given in Fig. 4. The Dvmin values slightly increase with the ion ¯uence re¯ecting the increasing damage. The relative large ¯uctuations are typical for implantations around the critical temperature. As can be seen the Dvmin values are remarkably larger for P than for In and the difference appears to be stronger for the á1 0 0ñ than for the á1 1 0ñ measurements. This indicates that
Fig. 3. PIXE á1 1 0ñ angular scans similar to Fig. 2, but with a higher ion ¯uence (NI 1 1015 cmÿ2 ).
separate atomic rows for In and P. Rows of atoms with low atomic number Z have narrower angular pro®les than rows of heavier atoms, which is indeed obtained for P (Z 15) and In (Z 49). A foreign atom with low concentration will then have a pro®le similar to that of the major constituent of the row where it resides. Despite the large errors for Se for both directions the Se angular distributions agree with the P distributions clearly. Therefore, Se must occupy regular P lattice
Fig. 4. Dierence in minimum yield Dvmin versus the ion ¯uence NI of 600 keV Se implanted InP. The crosses are the Dvmin obtained from the In part of RBS measurements. The other symbols represent the values extracted from In±L and P±K X-ray measurements corresponding to the symbols in Figs. 2 and 3.
518
F. Schrempel et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 515±519
axial channeling regime. The angular half-widths estimated from the PIXE curves allow the calculation of rms thermal vibration amplitudes u1 in the framework of LindhardÕs continuum model [10] using the equations developed by Barett [11]. In the case of a perfect crystal the angular halfwidth is given by [11]
the P sublattice is considerably more damaged than the In sublattice verifying that Se is incorporated into P sites. Thereby we do not ignore that the dierent X-ray absorption for In and P in¯uence the minimum yields. In the case of the á1 0 0ñ measurements 41% of the In signal and 56% of the P signal come from the damaged layer and the other parts come from the underlying substrate. Taking this into account the dierences between the Dvmin of In and P will be still larger than the values shown in Fig. 4. The In X-rays come from larger depths than the P X-rays, i.e. from regions of higher vmin if pure dechanneling is observed. Moreover the Dvmin of In are almost the same for both axes or slightly larger for the á1 1 0ñ than for the á1 0 0ñ axis indicating stronger damage, which indeed is expected for implantations close to the á1 0 0ñ axis. In the case of the P sublattice the opposite behaviour is observed. Possibly this can be explained by the formation of defect complexes with substitutional P atoms, which are preferentially oriented perpendicularly to the á1 0 0ñ axis. As can be seen in Fig. 1, the useful depth for the ions backscattered by In atoms is about 500 nm, but the transition from planar to pure axial channeling occurs in the deeper region [5,9]. The in¯uence of planar channeling near the surface leads to an increase of W1=2 and no extrapolation of the angular half-width W1=2 for the RBS angular scan curves to the surface can be performed (see [5]). In contrast, the X-rays are integrally measured with respect to the depth from the surfaces down to about 3 lm where we can assume pure
W1=2
1:2u1 0:8R W1 ; aTF
1
where aTF is the Thomas±Fermi radius and W1 is LindhardÕs critical angle for channeling [10]. The function R has been tabulated by Barett and W1 is given by r 2Z1 Z2 e2 ; W1 Ed
2
where Z1 and Z2 are the atomic numbers of the projectile and the target atom, E is the incidence energy of the projectile, e is the electronic charge and d is the atomic spacing along the row. Using both formulas given above and W1=2 for the perfect crystal estimated from the á1 0 0ñ scans we obtain and u1 0:11 A for In and P, reu1 0:09 A spectively (see Table 1). These values are in good agreement to DebyeÕs theory using a Debye temperature of 321 K for InP, which gives rms thermal for In and 0.166 A vibration amplitudes of 0.086 A for P. In the case of implanted samples u1 in Eq. (1) can be regarded as a mean value u1 which is determined by both the rms thermal vibration
Table 1 Angular half-width W1=2 , root-mean-square displacement u1 and mean displacement distance ra for In and P obtained by the measurement of á1 0 0ñ angular PIXE scans of 600 keV implanted InP Ion ¯uence NI (cmÿ2 )
0 2 1013 1 1014 4 1014 1 1015
Angular half-width W1=2 (°)
Root-mean-square displacement u1 (A)
Mean displacement distance ra (A)
In
P
In
P
In
P
0.55 0.53 0.55 0.51 0.51
0.39 0.38 0.38 0.37 0.35
0.090 0.094 0.090 0.098 0.098
0.110 0.112 0.112 0.119 0.133
± 0.10 0.09 0.14 0.14
± 0.12 0.12 0.16 0.23
F. Schrempel et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 515±519
amplitude u1 of the atoms not displaced and the mean displacement distance ra of the displaced lattice atoms caused by the implantation induced damage. With the corresponding mean values of the concentrations of displaced lattice atoms ndat one obtains r 1 ÿ ndat u21 ndat ra2 : 3 u1 The measured angular half-widths W1=2 and the u1 values calculated by Eq. (1) are given in Table 1. In [3±5] it has been shown that for implantations with low ion ¯uences above the critical temperature isolated point defects cause dominant lattice distortions, which results in large ndat values. At higher ¯uences the lattice distortion is reduced due to higher defect concentrations. Therefore, the mean concentration of displaced atoms ndat decreases and remains almost constant until amorphisation occurs. With ndat 0:33 for NI 21013 cmÿ2 and ndat 0:14 for NI > 2 1013 cmÿ2 taken from [4] the mean displacement distances ra were calculated by Eq. (3). The results are summarised in Table 1, and the following can be seen. The values represent the damage increasing with increasing ion ¯uence. The mean displacement distances ra obtained from the angular PIXE scans are lower than the values obtained by temperature for low and dependent RBS measurements (0.2 A 0.4±0.5 A for the higher ion ¯uences [4]). This is due to the eect that the analysed depth is much larger than the thickness of the damaged layer. If it is taken into account that only almost 50% of the X-ray signals come from the damaged layer both results are in agreement.
519
4. Summary Weakly damaged ion implanted InP layers have been studied by the measurement of RBS and PIXE angular scans. The results are: (i) Nearly all implanted Se atoms occupy regular lattice sites of the P sublattice. (ii) The P sublattice is more strongly damaged than the In sublattice. (iii) We expect the formation of defect complexes with substitutional P atoms, which are preferentially oriented perpendicularly to the á1 0 0ñ axis. (iv) The mean displacement distances estimated by the angular half scans almost agree with the values obtained by temperature dependent RBS measurements.
References [1] W. Wesch, Mater. Res. Soc. Symp. Proc. 300 (1993) 297. [2] E. Wendler, W. Wesch, Nucl. Instr. and Meth. B 73 (1993) 489. [3] E. Wendler, T. Opfermann, P.I. Gaiduk, J. Appl. Phys. 82 (11) (1997) 5965. [4] T. Opfermann, Diploma thesis, Friedrich-Schiller-Universit at Jena, 1995. [5] E. Wendler, F. Schrempel, P. M uller, K. G artner, W. Wesch, Nucl. Instr. and Meth. B 118 (1996) 367. [6] Q.F. Xiao, S. Hashimoto, W.M. Gibson, S.J. Pearton, Nucl. Instr. and Meth. B 45 (1990) 464. [7] A. Bontemps, J. Fontenille, A. GuivarcÕh, Phys. Lett. A 55 (1976) 373. [8] J.U. Andersen, N.G. Chechenin, Z.Z. Hua, Appl. Phys. Lett. 39 (1981) 758. [9] A. Desalvo, R. Rosa, Phys. Rev. B 9 (11) (1974) 4605. [10] J. Lindhard, K. Dan. Vidensk. Selskab. Mat.-Fys. Medd 34 (14) (1965). [11] J.H. Barett, Phys. Rev. B 3 (1971) 1527.