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Investigation of defects by RBS-channeling methods
Nuclear Instruments & Methods in Physics Research SectIon B
Nuclear Instruments and Methods in Physics Research B63 (1992) 59-63 North-Holland
Investigation
of defects by RBS-channeling
methods
G. Giitz, K. Giirtner and W. Wesch Friedrich-Schiller- UniLjersitiit,Institut
fiir Festkiirperphysik,
Max- Wien-Platz, 1, O-6900 Jena, Germany
The conventional RBS-channeling method permits the determination of the amount of displaced atoms in crystalline solids as a function of depth. The dependence of energy spectra of backscattered particles on the energy of the analyzing ions and on the temperature of the crystal to be investigated can give additional information about the geometrical configuration of displaced atoms and about the kind of defects in favoured cases. The physical basis of a discontinuous model for the dechanneling of ions by displaced atoms is described where especially the dependence of the Rutherford backscattering yield on the temperature is taken into consideration. The model is proved on typical examples as e.g. point defects in ion implanted GaAs layers, dislocation loops in ion implanted Si and lattice distortions in In,Ga, _,As crystals.
1. Introduction For about 20 years RBS-channeling has been used to study defects in crystals [l-15]. Defects in crystals are characterized by displaced atoms. By RBS-channeling investigations these displaced atoms can be detected because the relative Rutherford backscattering yield for ions incident parallel to a crystal axis or plane (RBS minimum yield ,y,,,) is increased due to direct scattering and dechanneling processes of the ions by their interactions with the displaced atoms. The dechanneling mechanisms are different for different kinds of defects because of the different correlations between the displacements of the lattice atoms. For point defects with randomly distributed displacement distances ra (perpendicular to the dechanneling direction) within an area belonging to one atomic string the defect density n,,(z) (relative number of displaced lattice atoms) can be calculated directly from the minimum yield x,&z) measured as a function of the depth using a two beam approximation [3]. In this model the beam is split into two parts: a random beam xr in which the ions can be backscattered by all regular and displaced atoms of the crystal and an aligned beam (1 - x,) where the ions are only backscattered from displaced atoms. The defect detisity is given by
$&i(Z) =
xmdz) -x,(z) 1 -x,(z)
(1)
The concentration profile of the displaced atoms can be calculated from eq. (1) by an iterative process [4]. A more general description of the dechanneling process is given by the discontinuous model described 0168-583X/92/$05.00
in refs. [11,12]. Using this model all kinds of defects yielding to dechanneling effects of ions can be treated. Besides point defects with randomly distributed displacements ra also point defects with fixed values of ra and extended defects as dislocations and stacking faults can be investigated. Further the description of lattice distortions is possible. In the model the energy and temperature dependence of the dechanneling process is included by which further information about the kind of defects can be achieved. After a short description of the basic idea of the discontinuous model some applications concerning point defects in ion-implanted GaAs crystals, dislocation loops in ion-implanted Si crystals, and lattice distortion in In,Ga,_,As crystals will be considered in this paper.
2. Discontinuous
model of dechanneling
A detailed description of the discontinuous model is given in refs. [11,12]. The basis of the model is the genera1 treatment of dechanneling by Lindhard [16]. Instead of a continuous distribution g(E, , z) of the transverse energy E I of the ions at depth z, the relative number g,(z) of ions with transverse energy between E I, _ 1 and E I, (with E I, = E I ,i/( i,,, - i), E = E@:/2, 1,5~critical angle) is the physical quantiG6f interest. It is determined by a system of differential equations
y where
= the
c Q&z)> dechanneling
0 1992 - Elsevier Science Publishers B.V. All rights reserved
matrix
Q,,
is given
by the
G. G6tz et al. / RBS-channelmg
60
probability per depth P,, for the transition from group j to group i:
Q,,= p,, - 6,
c
I
of an ion .
(3)
‘h,
methods
0,06 _
k
The Rutherford obtained by
backscattering
minimum
Xrnl” = C~&(Z)t
l.LMeV
I
!
He+ -N
exp. data 0 125 K
implanted
“/’
(100)
GaAs
o_a_O-O-a-O---.=
0
yield xrnln is
(4)
talc. (r,=O.O22
where II, is the relative probability for hitting a lattice atom.The dechanneling matrix is the sum of all contributions from statistically independent processes (electronic scattering, nuclear scattering, scattering on defects).
---
125 K
-
295K
nm)
a b
3. Applications 3.1. Point defects in ion-implanted
GaAs
As shown in ref. [ll] the temperature dependence of the minimum yield xmln is strongly influenced by the distance ra of displaced atoms perpendicular to their string. Fig. 1 gives a schematic illustration of this dependence where Axm,” is the difference between the minimum yields of the damaged crystal and the perfect crystal (Ax,,, = x,,,,” - ~,,,,~,~~~r) and A’x,,,,” is the difvalues for two temperatures ference of the Ax,,, = AxmJT1) Axmin(T2)I. As seen in fig. 1 (A’xm,n has negative values for small ra and positive A’xm,n values for larger ra. The strong dependence for small ra permits a very sensitive investigation of point defects yielding to small displacements of lattice atoms as in the case of vacancies and antisite defects. Results for N-implanted GaAs crystals are given in figs. 2 and 3 [17]. In fig. 2a the theoretical fits of AX,,,,” as a function of depth z for two temperatures are presented (for an ion fluence of 7 X 1013 N/cm’). As
randomly
dlstrlbuted
ra
0
of Ax,,,
temperature
dependence
position
1 0.8
z (,urn)
Fig. 2. (a) Depth dependence of the measured and calculated Axmln at temperatures of 125 and 295 K for 1.4 MeV He+ incident on (100) GaAs implanted at room temperature with 7x 1013 N+ cm-‘. (b) Depth dependence n,,(z) of displaced atoms calculated for ra = 0.022 nm [17].
can be clearly seen there is a negative temperature dependence because the difference of the backscattering yield Axmln is higher for the lower temperature. The fits exhibit a displacement distance ra = 0.022 nm and the depth profile of the displaced atoms shown in fig. 2b. For a higher fluence of implanted N-ions, 1 x 1016 N/cm’, the temperature dependence of AX,,,,” becomes positive and the experimental values can be well fitted by a displacement distance ra = 0.065 nm, as can be seen in fig. 3. Further investigations concerning the dependence of ra on the fluence and the flux for ion implanted GaAs crystals are described elsewhere [17,18]. loops in ion-implanted
Si
temperature
dependence negative
0.6
0.4 depth
3.2. Dislocation positwe
0.2
of AX,,,
ra lnm)
Fig. 1. Schematic illustration of the temperature dependence of A2xm,nat a fixed depth z as a function of the position r,.
The contribution of dislocations to the dechanneling can be described by an additional inertial force acting upon the ions in the neighbourhood of a dislocation [ll]. As an example the treatment of the dechanneling by dislocation loops in ion implanted silicon [19,20] will be shown. The geometrical configuration of the dislocation loops is given in fig. 4. The diameter of the circular dislocation loop is R. The Burgers vector b is parallel to the channeling axis z, both perpendicular to the
G. G&z
et ul. / RBS-channeling
methods
61
Fig. 4. Disiocation loop geometry.
z
c
Fig. 3. (a) Temperature dependence of the measured and calculated Axmin at temperatures of 125 and 295 K for 1.4 MeV He’ incident on (100) GaAs implanted at room temperature with lOI Nf cme2. (b) Depth dependence n,(r) of displaced atoms calculated for ra = 0.045 nm [17].
loop plane. The difference of the minimum yields AXmin after and before the implantation of 6 x 1Or5 Si+ cm-* (100 keV, furnace annealed 120 min at 950 0 C) into silicon obtained from the backscattering spectra of 0.7 MeV He+ ions incident along the (100) axis is shown in fig. .%I. By TEM measurements it was found [19] that the dislocation loops in the (100) plane with the Burgers vector b = 0.384 nm perpendicular to this plane have a loop radius of R = 67 nm. Using these values the depth distribution of the dislocation Ioops shown in fig. 5b was calculated. A comparison with the depth profile of the implanted ions achieved by TRIM calculation (dashed curve in fig. 5b) exhibits that the dislocation loops are generated in the region of the end of the range of the implanted Si’ ions.
depth‘ 2 ( rd
Fig. 5, (a) Depth dependence of Axmin for 0.7 MeV He * incident on (100) Si [19]. (b) Depth dependence of the dislocation density ndis,(z) calculated from Ay,,,Jz) [21] (full line). The dashed line represents the depth profile of the implanted Si+.
62
G.
Gdtz et al. / RLS-channeling
Fig. 6. Symmetric (a) and asymmetric (b) insertion of tetrahedron cell (solid line) in the VCA tion)
lattice
(virtual
crystal
approxima-
[21].
Though In,Ga,_,As has the same zincblende structure as GaAs or InAs there are distortions in the lattice yielding to local displacements of the In-, Ga-, and As-atoms from their lattice place. RBS-dechanneling is a powerful method to investigate such displacements. But in all cases the experimental results have to be compared with those of theoretical considerations to get quantitative information. As shown in detail in ref. [21] for In,Ga,_,As crystals the distortion yields both a narrow distribution of r, (mostly only two different values) for the As-atoms and a broad distribution of ra for the Ga- and In-atoms, where in the latter case the value of the standard deviation u of a Gauss-approximation of the distribution depends on the geometrical configuration of the lattice distortion. So the symmetric insertion of the tetrahedron cell (fig. 6a) gives (Y= 0.040 A and the asymmetric insertion of the tetrahedron cell (fig. 6b) u = 0.066 A.
I
1
ODE
- - -
The experimental results achieved independently by two groups (Flagmeyer and GHrtner [21] and Haga et al. [22]) for In,,,Ga,,,As-crystals are represented in fig. 7. The comparison with the theoretical curves simulating the dechanneling process for different distributions of r, exhibits that the best fit of the experimental data i,s given in the range between u = 0.055 A and u = 0.060 A. This is in good agreement with the assumption that in In0,,3Ga,,,As crystals equal numbers of symmetrically and antisymmetrically included tetrahedron cells are present.
4. Summary
3.3. Lattice distortion in In,Ga, _ x As crystals
0.10
methods
G=0~3554 G=0.0601
Fig. 7. Depth dependence of Axmin for 1.2 MeV He+ incident on (100) In,,,,Ga,,,,As crystals.
The discontinuous model of Gtirtner [ll] is a good tool simulating the dechanneling of ions due to the influence of defects. The comparison of experimental and theoretical results gives a detailed information about the geometrical configuration of displaced atoms caused by defects. In the case of point defects the distance of displaced atoms perpendicular to their string and the concentration profile of displaced atoms can be determined. For extended defects information about the type and the depth distribution can be achieved. In principle all distortions in crystal lattices yielding to displaced atoms can be investigated. In the paper the efficiency of the method is shown for point defects in ion implanted GaAs crystals, for dislocation loops in ion implanted Si, and for lattice distortions in In,Ga, _XAs crystals.
References 111W.K. Chu, J.W. Mayer and M.A. Nicolet, Backscattering Spectrometry (Academic Press, New York, San Fransisco, London, 1978). PI G. GGtz and K. Glrtner, High Energy Ion Beam Analysis of Solids (Akademie Verlag, Berlin, 1988). [31 E. Btigh, Can. J. Phys. 46 (1968) 653. [41 J.E. Westmoreland, J.W. Mayer, F.H. Eisen and B. Welch, Radiat. Eff. 6 (1970) 161. t51 ST. Picraux, J. Appl. Phys. 44 (1973) 587. [61 B.R. Appleton, Defects in Semiconductors, Proc. Mater. Res. Sot. Annual Meeting, Boston, 1980 (North-Holland, Amsterdam, 1981) p. 97. 171W.K. Chu, ibid., p. 117. Dl ST. Picraux, ibid., p. 135. [91 Y. Q&t, Phys. Status. Solidi 30 (1968) 713. DO1 Y. QukC, Ann. de Physique 5 (1970) 105. K. Hehl and G. Schlotzhauer, Nucl. Instr. [ill K. Gktner, and Meth. 216 (1983) 275, B4 (1984) 55 and B4 (1984) 63. and K. Hehl, Nucl. Instr. and Meth. B12 (1985) 205.
[121 K. Glrtner
G. G&z et al. / RBS-channeling [13] K. Girtner
[14] [15] [16] [17]
and A. Uguzzoni, Nucl. Instr. and Meth. B33 (1988) 607. N. Matsunami, T. Gotoh and N. Itoh, Radiat. Eff. 33 (1977) 209. N. Matsunami, T. Gotoh and N. Itoh, Nucl. Instr. and Meth. 149 (1978) 430. J. Lindhard. K. Dan, Vidensk. Selsk. Mat. Fys. Medd. 34 (1965) no. 14. G. Giitz, K. Girtner and W. Wesch, Nucl. Instr. and Meth. B50 (1990) 131.
methods
63
[18] E. Wendler, W. Wesch and G. Giitz, Nucl. Instr. and Meth. B.52 (1990) 57. [19] G.G. Bentini, M. Bianconi and M. Servidori, Nucl. Instr. and Meth. B18 (1987) 145. [20] K. Glrtner and A. Uguzzoni, Nucl. Instr. and Meth. B33 (1988) 607. [21] R. Flagmeyer and K. Gartner, Nucl. Instr. and Meth. B47 (1990) 160. [22] T. Haga, T. Kimura, Y. Abe, T. Fukui and H. Sato, Appl. Phys. Lett. 47 (1985) 1162.
Nuclear Instruments and Methods in Physics Research B63 (1992) 59-63 North-Holland
Investigation
of defects by RBS-channeling
methods
G. Giitz, K. Giirtner and W. Wesch Friedrich-Schiller- UniLjersitiit,Institut
fiir Festkiirperphysik,
Max- Wien-Platz, 1, O-6900 Jena, Germany
The conventional RBS-channeling method permits the determination of the amount of displaced atoms in crystalline solids as a function of depth. The dependence of energy spectra of backscattered particles on the energy of the analyzing ions and on the temperature of the crystal to be investigated can give additional information about the geometrical configuration of displaced atoms and about the kind of defects in favoured cases. The physical basis of a discontinuous model for the dechanneling of ions by displaced atoms is described where especially the dependence of the Rutherford backscattering yield on the temperature is taken into consideration. The model is proved on typical examples as e.g. point defects in ion implanted GaAs layers, dislocation loops in ion implanted Si and lattice distortions in In,Ga, _,As crystals.
1. Introduction For about 20 years RBS-channeling has been used to study defects in crystals [l-15]. Defects in crystals are characterized by displaced atoms. By RBS-channeling investigations these displaced atoms can be detected because the relative Rutherford backscattering yield for ions incident parallel to a crystal axis or plane (RBS minimum yield ,y,,,) is increased due to direct scattering and dechanneling processes of the ions by their interactions with the displaced atoms. The dechanneling mechanisms are different for different kinds of defects because of the different correlations between the displacements of the lattice atoms. For point defects with randomly distributed displacement distances ra (perpendicular to the dechanneling direction) within an area belonging to one atomic string the defect density n,,(z) (relative number of displaced lattice atoms) can be calculated directly from the minimum yield x,&z) measured as a function of the depth using a two beam approximation [3]. In this model the beam is split into two parts: a random beam xr in which the ions can be backscattered by all regular and displaced atoms of the crystal and an aligned beam (1 - x,) where the ions are only backscattered from displaced atoms. The defect detisity is given by
$&i(Z) =
xmdz) -x,(z) 1 -x,(z)
(1)
The concentration profile of the displaced atoms can be calculated from eq. (1) by an iterative process [4]. A more general description of the dechanneling process is given by the discontinuous model described 0168-583X/92/$05.00
in refs. [11,12]. Using this model all kinds of defects yielding to dechanneling effects of ions can be treated. Besides point defects with randomly distributed displacements ra also point defects with fixed values of ra and extended defects as dislocations and stacking faults can be investigated. Further the description of lattice distortions is possible. In the model the energy and temperature dependence of the dechanneling process is included by which further information about the kind of defects can be achieved. After a short description of the basic idea of the discontinuous model some applications concerning point defects in ion-implanted GaAs crystals, dislocation loops in ion-implanted Si crystals, and lattice distortion in In,Ga,_,As crystals will be considered in this paper.
2. Discontinuous
model of dechanneling
A detailed description of the discontinuous model is given in refs. [11,12]. The basis of the model is the genera1 treatment of dechanneling by Lindhard [16]. Instead of a continuous distribution g(E, , z) of the transverse energy E I of the ions at depth z, the relative number g,(z) of ions with transverse energy between E I, _ 1 and E I, (with E I, = E I ,i/( i,,, - i), E = E@:/2, 1,5~critical angle) is the physical quantiG6f interest. It is determined by a system of differential equations
y where
= the
c Q&z)> dechanneling
0 1992 - Elsevier Science Publishers B.V. All rights reserved
matrix
Q,,
is given
by the
G. G6tz et al. / RBS-channelmg
60
probability per depth P,, for the transition from group j to group i:
Q,,= p,, - 6,
c
I
of an ion .
(3)
‘h,
methods
0,06 _
k
The Rutherford obtained by
backscattering
minimum
Xrnl” = C~&(Z)t
l.LMeV
I
!
He+ -N
exp. data 0 125 K
implanted
“/’
(100)
GaAs
o_a_O-O-a-O---.=
0
yield xrnln is
(4)
talc. (r,=O.O22
where II, is the relative probability for hitting a lattice atom.The dechanneling matrix is the sum of all contributions from statistically independent processes (electronic scattering, nuclear scattering, scattering on defects).
---
125 K
-
295K
nm)
a b
3. Applications 3.1. Point defects in ion-implanted
GaAs
As shown in ref. [ll] the temperature dependence of the minimum yield xmln is strongly influenced by the distance ra of displaced atoms perpendicular to their string. Fig. 1 gives a schematic illustration of this dependence where Axm,” is the difference between the minimum yields of the damaged crystal and the perfect crystal (Ax,,, = x,,,,” - ~,,,,~,~~~r) and A’x,,,,” is the difvalues for two temperatures ference of the Ax,,, = AxmJT1) Axmin(T2)I. As seen in fig. 1 (A’xm,n has negative values for small ra and positive A’xm,n values for larger ra. The strong dependence for small ra permits a very sensitive investigation of point defects yielding to small displacements of lattice atoms as in the case of vacancies and antisite defects. Results for N-implanted GaAs crystals are given in figs. 2 and 3 [17]. In fig. 2a the theoretical fits of AX,,,,” as a function of depth z for two temperatures are presented (for an ion fluence of 7 X 1013 N/cm’). As
randomly
dlstrlbuted
ra
0
of Ax,,,
temperature
dependence
position
1 0.8
z (,urn)
Fig. 2. (a) Depth dependence of the measured and calculated Axmln at temperatures of 125 and 295 K for 1.4 MeV He+ incident on (100) GaAs implanted at room temperature with 7x 1013 N+ cm-‘. (b) Depth dependence n,,(z) of displaced atoms calculated for ra = 0.022 nm [17].
can be clearly seen there is a negative temperature dependence because the difference of the backscattering yield Axmln is higher for the lower temperature. The fits exhibit a displacement distance ra = 0.022 nm and the depth profile of the displaced atoms shown in fig. 2b. For a higher fluence of implanted N-ions, 1 x 1016 N/cm’, the temperature dependence of AX,,,,” becomes positive and the experimental values can be well fitted by a displacement distance ra = 0.065 nm, as can be seen in fig. 3. Further investigations concerning the dependence of ra on the fluence and the flux for ion implanted GaAs crystals are described elsewhere [17,18]. loops in ion-implanted
Si
temperature
dependence negative
0.6
0.4 depth
3.2. Dislocation positwe
0.2
of AX,,,
ra lnm)
Fig. 1. Schematic illustration of the temperature dependence of A2xm,nat a fixed depth z as a function of the position r,.
The contribution of dislocations to the dechanneling can be described by an additional inertial force acting upon the ions in the neighbourhood of a dislocation [ll]. As an example the treatment of the dechanneling by dislocation loops in ion implanted silicon [19,20] will be shown. The geometrical configuration of the dislocation loops is given in fig. 4. The diameter of the circular dislocation loop is R. The Burgers vector b is parallel to the channeling axis z, both perpendicular to the
G. G&z
et ul. / RBS-channeling
methods
61
Fig. 4. Disiocation loop geometry.
z
c
Fig. 3. (a) Temperature dependence of the measured and calculated Axmin at temperatures of 125 and 295 K for 1.4 MeV He’ incident on (100) GaAs implanted at room temperature with lOI Nf cme2. (b) Depth dependence n,(r) of displaced atoms calculated for ra = 0.045 nm [17].
loop plane. The difference of the minimum yields AXmin after and before the implantation of 6 x 1Or5 Si+ cm-* (100 keV, furnace annealed 120 min at 950 0 C) into silicon obtained from the backscattering spectra of 0.7 MeV He+ ions incident along the (100) axis is shown in fig. .%I. By TEM measurements it was found [19] that the dislocation loops in the (100) plane with the Burgers vector b = 0.384 nm perpendicular to this plane have a loop radius of R = 67 nm. Using these values the depth distribution of the dislocation Ioops shown in fig. 5b was calculated. A comparison with the depth profile of the implanted ions achieved by TRIM calculation (dashed curve in fig. 5b) exhibits that the dislocation loops are generated in the region of the end of the range of the implanted Si’ ions.
depth‘ 2 ( rd
Fig. 5, (a) Depth dependence of Axmin for 0.7 MeV He * incident on (100) Si [19]. (b) Depth dependence of the dislocation density ndis,(z) calculated from Ay,,,Jz) [21] (full line). The dashed line represents the depth profile of the implanted Si+.
62
G.
Gdtz et al. / RLS-channeling
Fig. 6. Symmetric (a) and asymmetric (b) insertion of tetrahedron cell (solid line) in the VCA tion)
lattice
(virtual
crystal
approxima-
[21].
Though In,Ga,_,As has the same zincblende structure as GaAs or InAs there are distortions in the lattice yielding to local displacements of the In-, Ga-, and As-atoms from their lattice place. RBS-dechanneling is a powerful method to investigate such displacements. But in all cases the experimental results have to be compared with those of theoretical considerations to get quantitative information. As shown in detail in ref. [21] for In,Ga,_,As crystals the distortion yields both a narrow distribution of r, (mostly only two different values) for the As-atoms and a broad distribution of ra for the Ga- and In-atoms, where in the latter case the value of the standard deviation u of a Gauss-approximation of the distribution depends on the geometrical configuration of the lattice distortion. So the symmetric insertion of the tetrahedron cell (fig. 6a) gives (Y= 0.040 A and the asymmetric insertion of the tetrahedron cell (fig. 6b) u = 0.066 A.
I
1
ODE
- - -
The experimental results achieved independently by two groups (Flagmeyer and GHrtner [21] and Haga et al. [22]) for In,,,Ga,,,As-crystals are represented in fig. 7. The comparison with the theoretical curves simulating the dechanneling process for different distributions of r, exhibits that the best fit of the experimental data i,s given in the range between u = 0.055 A and u = 0.060 A. This is in good agreement with the assumption that in In0,,3Ga,,,As crystals equal numbers of symmetrically and antisymmetrically included tetrahedron cells are present.
4. Summary
3.3. Lattice distortion in In,Ga, _ x As crystals
0.10
methods
G=0~3554 G=0.0601
Fig. 7. Depth dependence of Axmin for 1.2 MeV He+ incident on (100) In,,,,Ga,,,,As crystals.
The discontinuous model of Gtirtner [ll] is a good tool simulating the dechanneling of ions due to the influence of defects. The comparison of experimental and theoretical results gives a detailed information about the geometrical configuration of displaced atoms caused by defects. In the case of point defects the distance of displaced atoms perpendicular to their string and the concentration profile of displaced atoms can be determined. For extended defects information about the type and the depth distribution can be achieved. In principle all distortions in crystal lattices yielding to displaced atoms can be investigated. In the paper the efficiency of the method is shown for point defects in ion implanted GaAs crystals, for dislocation loops in ion implanted Si, and for lattice distortions in In,Ga, _XAs crystals.
References 111W.K. Chu, J.W. Mayer and M.A. Nicolet, Backscattering Spectrometry (Academic Press, New York, San Fransisco, London, 1978). PI G. GGtz and K. Glrtner, High Energy Ion Beam Analysis of Solids (Akademie Verlag, Berlin, 1988). [31 E. Btigh, Can. J. Phys. 46 (1968) 653. [41 J.E. Westmoreland, J.W. Mayer, F.H. Eisen and B. Welch, Radiat. Eff. 6 (1970) 161. t51 ST. Picraux, J. Appl. Phys. 44 (1973) 587. [61 B.R. Appleton, Defects in Semiconductors, Proc. Mater. Res. Sot. Annual Meeting, Boston, 1980 (North-Holland, Amsterdam, 1981) p. 97. 171W.K. Chu, ibid., p. 117. Dl ST. Picraux, ibid., p. 135. [91 Y. Q&t, Phys. Status. Solidi 30 (1968) 713. DO1 Y. QukC, Ann. de Physique 5 (1970) 105. K. Hehl and G. Schlotzhauer, Nucl. Instr. [ill K. Gktner, and Meth. 216 (1983) 275, B4 (1984) 55 and B4 (1984) 63. and K. Hehl, Nucl. Instr. and Meth. B12 (1985) 205.
[121 K. Glrtner
G. G&z et al. / RBS-channeling [13] K. Girtner
[14] [15] [16] [17]
and A. Uguzzoni, Nucl. Instr. and Meth. B33 (1988) 607. N. Matsunami, T. Gotoh and N. Itoh, Radiat. Eff. 33 (1977) 209. N. Matsunami, T. Gotoh and N. Itoh, Nucl. Instr. and Meth. 149 (1978) 430. J. Lindhard. K. Dan, Vidensk. Selsk. Mat. Fys. Medd. 34 (1965) no. 14. G. Giitz, K. Girtner and W. Wesch, Nucl. Instr. and Meth. B50 (1990) 131.
methods
63
[18] E. Wendler, W. Wesch and G. Giitz, Nucl. Instr. and Meth. B.52 (1990) 57. [19] G.G. Bentini, M. Bianconi and M. Servidori, Nucl. Instr. and Meth. B18 (1987) 145. [20] K. Glrtner and A. Uguzzoni, Nucl. Instr. and Meth. B33 (1988) 607. [21] R. Flagmeyer and K. Gartner, Nucl. Instr. and Meth. B47 (1990) 160. [22] T. Haga, T. Kimura, Y. Abe, T. Fukui and H. Sato, Appl. Phys. Lett. 47 (1985) 1162.