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Phonon spectroscopy of oxygen defects in silicon and germanium
ELSEVIER
Physica B 219&220 (1996) 730 733
Phonon spectroscopy of oxygen defects in silicon and germanium Kurt Lal3mann Universitgit Stuttyart, 1. Physikalisches Institut, Pfaffenwaldrin9 57, D-70550 Stuttgart, Germany
Abstract Oxygen as an impurity in Si and Ge and in III-V-compounds such as GaAs or GaP has been an object of research since decades because of its complicated incorporation as well as its technical relevance. Phonon spectroscopy with superconducting tunnel junctions by its high sensitivity, good resolution, and convenient tunability is most appropriate for the investigation of the low-energy vibrational states of the interstitial oxygen as well as of the various nanoscopic precipitates with dimensions of the size of the phonon wavelength.
1. Interstitial oxygen in silicon and germanium In the following we shall review the contribution of phonon spectroscopy to the state of knowledge of oxygenrelated defects in the elemental semiconductors silicon and germanium. The essentials of the spectroscopic technique using superconducting tunneling junctions as bias tunable phonon generators and as high-pass phonon detectors have been discussed by Eisenmenger in Ref. [1] (see also Ref. [2]). For a recent review on oxygen-related defects in silicon, see Ref. [3]. Oxygen as a point defect in as-grown Si and Ge is an electrically inactive interstitial slightly off-axis between two nearest-neighbour lattice atoms in a (111 )-direction. Important information on the details of the structure has come from the investigation of the IR bands related to its motional modes and especially from the sequence of lowestlying states in the range of FIR. These depend sensitively on the microscopic parameters such as the height of the axial barrier against inversion or the sixfold angular modulation of the potential ditch due to the two neighbouring tripods. In silicon this sequence of low-lying levels between 3.63 and 14.93 meV above the ground state has been investigated by FIR absorption and analysed in terms of a two-dimensional harmonic oscillator perturbed by the axial barrier or, alternatively, in terms of a non-rigid rotator [4]. A distance of the radial minimum of the model potential of only 22 pm was obtained as compared to the 235 pm distance of the Si atoms in the unperturbed lattice. Somewhat 0921-4526/96/$15.00 @ 1996 Elsevier Science B.V. All rights reserved SSDI0921-4526(95)00868-3
larger values follow from recent cluster calculations [5, 6], namely 38 and 35 pm, respectively, for the radial minimum and 308 and 311 pm for the Si-Si distance with the oxygen in between. The coupling to the lattice of this nearly stretched configuration is weak resulting in a rather narrow line width due to lifetime broadening or inhomogeneous broadening from static internal strains: About 15 geV has been obtained with phonon spectroscopy [7, 2], FIR-laser spectroscopy [8], and backward wave tube spectroscopy [9] for the 3.63 meV transition. Although the phonon coupling is weak the high resolution of phonon spectroscopy allows the detection of concentrations as low as 7x 1019m-3 [2]. This high sensitivity has facilitated at higher oxygen concentrations the detection of a series of satellite lines to the 3.63 meV transition [10, 7], as shown in Fig. 1. From the quadratic dependence of their depths on oxygen concentration it has been concluded that it is the mutual strain interaction of the statistically few, more or less close oxygen pairs that shifts the resonance depending on the location and orientation of the partner [7]. An isotropic continuum approximation for the strain interaction gives reasonable overall agreement with the observed strength and frequency range of the satellites. Discrete lines in this approximation would correspond to pair distances smaller than two lattice constants; for larger distances the lines should merge into a continuum around the unshifted resonance. Since the pair interaction energy within this approximation is higher in the case of down-shifted resonances the relative occupation of the low and high-frequency portion of the band of
K. Laflmann/Physica B 219&220 (1996) 730-733
phonon energy [ meV] 2
3
4
I
I
I
5
6
I
Is0 160 [16od =
c-
4.5.1017 c m - 3 •7.1.1017 c m - 3 13.9.1017 c m - 3
t
It' t Jlt tit tit
¢-
I 2A detectorthreshold t
I
i
i
i
0
200
400
600
800
I
I
1 0 0 0 1200
I
1400
phonon frequency [GHz]
Fig. 1. Phonon scattering in Si:O with higher concentrations of interstitial oxygen. With increasing concentration the main resonance at 3.63 meV broadens instrumentally and satellites appear at higher frequencies. The sample with the highest concentration is special in that it had not experienced a 1000°C anneal after crystal growth. All such samples with high oxygen concentration show a low-frequency satellite at 790 GHz, which vanishes after annealing [20]. satellites will depend on cooling rate versus jump rates between the various configurations. This could explain that mainly high-frequency satellites are observed. A line at 790 GHz, i.e. below the main resonance was observed only in samples with oxygen concentrations > 1023 m -3 that had not experienced a 2 h 1090°C annealing by the supplier. This line disappeared after annealing at 1000°C for 30 min which would be consistent with the above reasoning. Investigating the variations in the satellite band with specific annealing (under stress) and quenching procedures one should obtain information on the oxygen interaction and agglomeration on a microscopic basis. In germanium a more off-axis position of the interstitial oxygen was estimated from high-resolution IRmeasurements [11] as well as from recent cluster calculations [6]. The high sensitivity and wide-range tunability allowed to detect the corresponding transitions between 0.18 and 4.5 meV, i.e. one order of magnitude below those of interstitial oxygen in silicon [12]. The state at 0.18 meV showed up as a doublet partner 0.18 meV below the transitions from the ground state because of its thermal occupation. The sequence could be fitted quite well to the states l = 4-1 to l = 4-5 above the ground state 1 = 0 of a rigid rotator (RR) hindered by a 0.28 meV angular modulation of the potential ditch due to the influence of the six next-nearest neighbours manifest by a splitting of
731
the 1 = 4-3 state. The analysis yields 93 pm for the radial minimum of the potential. This is distinctly larger than the value of 57 pm obtained from cluster calculations [6]. Deviations from the RR sequence are expected for the higher levels due to finite height of the central barrier. However, strong isotope scattering in natural Ge makes phonon spectroscopy above 4 meV rather difficult. In a 300 gm thin sample with high Og concentration we find small resonance dips at 4.57 and 4.75 meV, i.e. again 0.18 meV apart. We tentatively ascribe this doublet to an OMevel at 4.75 meV (i.e. distinctly below the 6 meV expected for the l = + 6 level in the RR limit) and take profit of the model calculation of Yamada-Kaneta et al. for varying height of the harmonic central barrier within a quartic two-dimensional oscillator potential as summarized in Fig. 3 in Ref. [13]). We can fit the whole sequence for the dimensionless parameter Anon = - 8 . 7 for the energy parameter Euni = 0.64 meV arriving (within this model) at a central barrier height of 12.1 meV and a radial minimum of the potential ditch at 93 pm, i.e. identical to the value obtained in the RR limit. The fit to the rotational levels with this model calculation is even somewhat better than in the RR-limit As pointed out in Ref. [14] the RR-fit is also improved by including the centrifugal correction term in the case of the twodimensional harmonic oscillator as was similarly done in Ref. [4] for the states of Oi in Si. In this case, however, a much higher value for the first excited radial level is estimated from the fit, namely, 9.2 meV above the ground state, so, much depends on the model potential used. It is, therefore, of interest to locate the higher states and to determine their character. Isotopically enriched, high-quality Ge might be helpful to reduce the phonon scattering at higher energies. Additional information on microscopic parameters or check of first principles calculations can be obtained from the stress dependence. The shift or splitting of levels is determined by the changes in bond lengths and angles of the complex to be related to the external stress.
2. Oxygen-related complexes in silicon and germanium Upon annealing Ge : O,. and Si : Og at temperatures around 350°C and 450°C, respectively, a series of oxygen-related shallow double donors is formed (so-called thermal donors, TD) of which the microscopic nature as yet is not completely clarified. From the models presented so far, lowlying motional resonances (e.g. from the oxygen interstitials involved) cannot be excluded but have as yet not been observed. In Ge the ionization energies of these donors are between ~15 meV and ~20 meV, so that it might be interesting to look for phonon-induced ionization as in the case of single donors in Ge [15]. The splitting of the ground state due to central cell effects and to electron-electron interaction from optical investigations [ 16] is expected to be in the lower meV
732
K. Laflmann / Physica B 219 &220 (1996) 730 733
phonon frequency [GHz]
0
100
200
1::I [:::o]c
5
300
400
500
600
700
ca. 100 MPa. f
not annealed ]
120hat 735C
• o.,,x,o"cm
2/,ca7 7 +2,5hat 1220C
O)
o.o
o.s
1.o
1.5
2.0
2.5
3.0
+2.5hat 1270'C ]
phonon energy [meV] Fig. 2. Stress dependence of the phonon transmission through a G e : O sample with high concentration of thermal donors ([TD]=3.Sx 1022 m-3). Under stress various resonances of the interstitial oxygen become visible. The small SNR is due to poor quality of the detector junction [21]. range and thus should be observable as distinct phonon scattering resonances. Instead, we find for higher TD concentrations in Ge a broad, nearly unstructured phonon scattering below about 2.2 meV the details varying somewhat from sample to sample. In some cases a depression of the transmission around 2 meV can be distinguished. In any case the additional scattering is reduced (not shifted) by uniaxial stress. Fig. 2 shows an example for very high concentration of TD. Experiments with specific annealing procedures, counterdoping for compensation, together with comparative IR-measurements are planned to clarify whether the scattering is due to motional or electronic resonances or to a combination of both in the case of a Jahn-Teller effect and to which extent oxygen-related precipitates may be involved. Annealing oxygen-doped silicon at temperatures above about 500°C leads to various types of oxygen-related precipitates with dimensions down to several nanometers. So, phonon scattering might be expected due to geometrical resonances similar to previous observations of Ca clusters in irradiated CaF2 [17]. First experiments show that there is in fact additional phonon scattering due to oxygen precipitation and that there are distinct differences for carbon-lean and carbon-rich material. In the first case the scattering is mainly inelastic indicative of amorphous SiO2 clusters, whereas in the latter case the scattering is mainly elastic and after annealing above 1220°C an extra scattering around 400 GHz is found corresponding to a wavelength of about 10 nm of
I
I
0
I
400
I
I
800
1200
phonon frequency [GHz] Fig. 3. Change ofphonon transmission spectra of carbon-rich Cz-Si with annealing. A line at 330 GHz, correlated with a C-O-complex, vanishes by annealing at 735°C. Additional scattering around 400 GHz appears after annealing 1220°C. Annealing at 1270°C dissolves and perhaps sharpens the distribution [22]. the transverse phonons. Gupta et al. [18] concluded from small angle neutron scattering in carbon-rich material on spherical precipitates of about 9 nm diameter after annealing at 720°C which consist partially of [3-SIC. An example for phonon transmission spectra is given in Fig. 3.
3. Conclusion
From the foregoing it is evident that high-resolution wideband tunable phonon spectroscopy with superconducting tunnel junctions can contribute much to the understanding of oxygen defects in silicon and germanium and possibly so also in other semiconductors such as GaAs [ 19] or GaP.
Acknowledgements
The work reviewed here is an outcome of the activities of quite a group at Stuttgart University. I should like to name M. Welte, W. Forkel, E. Dittrich, W. Scheitler,
K. Laflmann/ Physica B 219&220 (1996) 730 733 M. Gienger, C. Wurster, M. Glaser, G. Schrag, F. Zeller, and, with his steady creative and experienced involvement, W. Eisenmenger. We profited from helpful discussions with H. YamadaKaneta concerning the level sequence in G e : Oi. We are indepted to E.E. Haller, W. Kaiser, and W. Zulehner for the kind supply of appropriate samples. Most of the research reported here has been financially supported by the Deutsche Forschungsgemeinschaft which is gratefully acknowledged.
References [1 ] W. Eisenmenger, in: Physical Acoustics 12, eds. W.P. Mason and R.N. Thurston (Academic Press, New York, 1976) p. 79 [2] C. Wurster, E. Dinrich, W. Scheitler, K. LaBmann, W. Eisenmenger and W. Zulehner, Physica B 219&220 (1996) 763. [3] F. Shimura (ed.), Oxygen in Silicon, in: Semiconductors and Semimetals, Vol. 42, eds. R.K. Willardson, A.C. Beer and E.R. Weber (1994). [4] D.R. Bosomworth, W. Hayes, A.R.L. Spray and G.D. Watkins, Proc. Roy. Soc. Lond. A 317 (1970) 133. [5] C. Kaneta, H. Yamada-Kaneta and A. Ohsawa, Mat. Sci. Forum 38-41 (1989) 323. [6] A. Liz6n-NordstrSm and F. YndurS.in, Solid State Commun. 89 (1994) 819. [7] E. Dittrich, W. Scheitler and W. Eisenmenger, Jpn J. Appl. Phys. 39 (Suppl. 26-3) (1987) 873.
733
[8] U. Werling and K.F. Renk, Phys. Rev. B 39 (1989) 1286. [9] A.A. Volkov, Yu.G. Goncharov, V.P. Kalinushkin, G.V. Kozlov and A. M. Prokhorov, Fiz. Tverd. Tela 31 (1989) 262 [Sov. Phys. Solid State 31 (1989) 1249]. [10] W. Forkel, Thesis, Stuttgart (1977). [11] B. Pajot and P. Clauws, in: Proc. 18th Int. Conf. on Phys. of Semic., Stockholm, 1986, Vol. 2 (World Scientific, Singapore, 1987) p. 911. [12] M. Gienger, M. Glaser and K. LaBmann, Solid State Commun. 86 (1993) 285. [13] H. Yamada-Kaneta, C. Kaneta and T. Ogawa, Phys. Rev, B 42 (1990) 9650. [14] E. Artacho and F. Yndurfiin, in: Proc. 18th Int. Conf. on Defects in Semiconductors, Sendai, 1995 (Trans Tech Publications, Switzerland), to be published. [15] M. Gienger, P. GroB and K. Lal3mann, Phys. Rev. Lett. 64 (1990) 1138. [16] P. Clauws and J. Vennik, Mater. Sci. Forum 10-12 (1986) 941. [17] C. Wurster, K. Lal3mann and W. Eisenmenger, Phys. Rev. Lett. 70 (1993) 3451. [18] S. Gupta, S. Messolares, J.R. Schneider, R.J. Stewart and W. Zulehner, Semicond. Sci. Technol. 7 (1992) 6. [19] F. Maier, R. Eilenberger, W. Beck and K. LaBmann, in: Proc. 18th Int. Conf. on Defects in Semiconductors, Sendai, 1995 (Trans Tech Publications, Switzerland), to be published. [20] E. Dittrich, Thesis, Stuttgart (1989). [21] F. Zeller, Diplomarbeit, Stuttgart (1994). [22] G. Schrag, Diplomarbeit, Stuttgart (1993).
Physica B 219&220 (1996) 730 733
Phonon spectroscopy of oxygen defects in silicon and germanium Kurt Lal3mann Universitgit Stuttyart, 1. Physikalisches Institut, Pfaffenwaldrin9 57, D-70550 Stuttgart, Germany
Abstract Oxygen as an impurity in Si and Ge and in III-V-compounds such as GaAs or GaP has been an object of research since decades because of its complicated incorporation as well as its technical relevance. Phonon spectroscopy with superconducting tunnel junctions by its high sensitivity, good resolution, and convenient tunability is most appropriate for the investigation of the low-energy vibrational states of the interstitial oxygen as well as of the various nanoscopic precipitates with dimensions of the size of the phonon wavelength.
1. Interstitial oxygen in silicon and germanium In the following we shall review the contribution of phonon spectroscopy to the state of knowledge of oxygenrelated defects in the elemental semiconductors silicon and germanium. The essentials of the spectroscopic technique using superconducting tunneling junctions as bias tunable phonon generators and as high-pass phonon detectors have been discussed by Eisenmenger in Ref. [1] (see also Ref. [2]). For a recent review on oxygen-related defects in silicon, see Ref. [3]. Oxygen as a point defect in as-grown Si and Ge is an electrically inactive interstitial slightly off-axis between two nearest-neighbour lattice atoms in a (111 )-direction. Important information on the details of the structure has come from the investigation of the IR bands related to its motional modes and especially from the sequence of lowestlying states in the range of FIR. These depend sensitively on the microscopic parameters such as the height of the axial barrier against inversion or the sixfold angular modulation of the potential ditch due to the two neighbouring tripods. In silicon this sequence of low-lying levels between 3.63 and 14.93 meV above the ground state has been investigated by FIR absorption and analysed in terms of a two-dimensional harmonic oscillator perturbed by the axial barrier or, alternatively, in terms of a non-rigid rotator [4]. A distance of the radial minimum of the model potential of only 22 pm was obtained as compared to the 235 pm distance of the Si atoms in the unperturbed lattice. Somewhat 0921-4526/96/$15.00 @ 1996 Elsevier Science B.V. All rights reserved SSDI0921-4526(95)00868-3
larger values follow from recent cluster calculations [5, 6], namely 38 and 35 pm, respectively, for the radial minimum and 308 and 311 pm for the Si-Si distance with the oxygen in between. The coupling to the lattice of this nearly stretched configuration is weak resulting in a rather narrow line width due to lifetime broadening or inhomogeneous broadening from static internal strains: About 15 geV has been obtained with phonon spectroscopy [7, 2], FIR-laser spectroscopy [8], and backward wave tube spectroscopy [9] for the 3.63 meV transition. Although the phonon coupling is weak the high resolution of phonon spectroscopy allows the detection of concentrations as low as 7x 1019m-3 [2]. This high sensitivity has facilitated at higher oxygen concentrations the detection of a series of satellite lines to the 3.63 meV transition [10, 7], as shown in Fig. 1. From the quadratic dependence of their depths on oxygen concentration it has been concluded that it is the mutual strain interaction of the statistically few, more or less close oxygen pairs that shifts the resonance depending on the location and orientation of the partner [7]. An isotropic continuum approximation for the strain interaction gives reasonable overall agreement with the observed strength and frequency range of the satellites. Discrete lines in this approximation would correspond to pair distances smaller than two lattice constants; for larger distances the lines should merge into a continuum around the unshifted resonance. Since the pair interaction energy within this approximation is higher in the case of down-shifted resonances the relative occupation of the low and high-frequency portion of the band of
K. Laflmann/Physica B 219&220 (1996) 730-733
phonon energy [ meV] 2
3
4
I
I
I
5
6
I
Is0 160 [16od =
c-
4.5.1017 c m - 3 •7.1.1017 c m - 3 13.9.1017 c m - 3
t
It' t Jlt tit tit
¢-
I 2A detectorthreshold t
I
i
i
i
0
200
400
600
800
I
I
1 0 0 0 1200
I
1400
phonon frequency [GHz]
Fig. 1. Phonon scattering in Si:O with higher concentrations of interstitial oxygen. With increasing concentration the main resonance at 3.63 meV broadens instrumentally and satellites appear at higher frequencies. The sample with the highest concentration is special in that it had not experienced a 1000°C anneal after crystal growth. All such samples with high oxygen concentration show a low-frequency satellite at 790 GHz, which vanishes after annealing [20]. satellites will depend on cooling rate versus jump rates between the various configurations. This could explain that mainly high-frequency satellites are observed. A line at 790 GHz, i.e. below the main resonance was observed only in samples with oxygen concentrations > 1023 m -3 that had not experienced a 2 h 1090°C annealing by the supplier. This line disappeared after annealing at 1000°C for 30 min which would be consistent with the above reasoning. Investigating the variations in the satellite band with specific annealing (under stress) and quenching procedures one should obtain information on the oxygen interaction and agglomeration on a microscopic basis. In germanium a more off-axis position of the interstitial oxygen was estimated from high-resolution IRmeasurements [11] as well as from recent cluster calculations [6]. The high sensitivity and wide-range tunability allowed to detect the corresponding transitions between 0.18 and 4.5 meV, i.e. one order of magnitude below those of interstitial oxygen in silicon [12]. The state at 0.18 meV showed up as a doublet partner 0.18 meV below the transitions from the ground state because of its thermal occupation. The sequence could be fitted quite well to the states l = 4-1 to l = 4-5 above the ground state 1 = 0 of a rigid rotator (RR) hindered by a 0.28 meV angular modulation of the potential ditch due to the influence of the six next-nearest neighbours manifest by a splitting of
731
the 1 = 4-3 state. The analysis yields 93 pm for the radial minimum of the potential. This is distinctly larger than the value of 57 pm obtained from cluster calculations [6]. Deviations from the RR sequence are expected for the higher levels due to finite height of the central barrier. However, strong isotope scattering in natural Ge makes phonon spectroscopy above 4 meV rather difficult. In a 300 gm thin sample with high Og concentration we find small resonance dips at 4.57 and 4.75 meV, i.e. again 0.18 meV apart. We tentatively ascribe this doublet to an OMevel at 4.75 meV (i.e. distinctly below the 6 meV expected for the l = + 6 level in the RR limit) and take profit of the model calculation of Yamada-Kaneta et al. for varying height of the harmonic central barrier within a quartic two-dimensional oscillator potential as summarized in Fig. 3 in Ref. [13]). We can fit the whole sequence for the dimensionless parameter Anon = - 8 . 7 for the energy parameter Euni = 0.64 meV arriving (within this model) at a central barrier height of 12.1 meV and a radial minimum of the potential ditch at 93 pm, i.e. identical to the value obtained in the RR limit. The fit to the rotational levels with this model calculation is even somewhat better than in the RR-limit As pointed out in Ref. [14] the RR-fit is also improved by including the centrifugal correction term in the case of the twodimensional harmonic oscillator as was similarly done in Ref. [4] for the states of Oi in Si. In this case, however, a much higher value for the first excited radial level is estimated from the fit, namely, 9.2 meV above the ground state, so, much depends on the model potential used. It is, therefore, of interest to locate the higher states and to determine their character. Isotopically enriched, high-quality Ge might be helpful to reduce the phonon scattering at higher energies. Additional information on microscopic parameters or check of first principles calculations can be obtained from the stress dependence. The shift or splitting of levels is determined by the changes in bond lengths and angles of the complex to be related to the external stress.
2. Oxygen-related complexes in silicon and germanium Upon annealing Ge : O,. and Si : Og at temperatures around 350°C and 450°C, respectively, a series of oxygen-related shallow double donors is formed (so-called thermal donors, TD) of which the microscopic nature as yet is not completely clarified. From the models presented so far, lowlying motional resonances (e.g. from the oxygen interstitials involved) cannot be excluded but have as yet not been observed. In Ge the ionization energies of these donors are between ~15 meV and ~20 meV, so that it might be interesting to look for phonon-induced ionization as in the case of single donors in Ge [15]. The splitting of the ground state due to central cell effects and to electron-electron interaction from optical investigations [ 16] is expected to be in the lower meV
732
K. Laflmann / Physica B 219 &220 (1996) 730 733
phonon frequency [GHz]
0
100
200
1::I [:::o]c
5
300
400
500
600
700
ca. 100 MPa. f
not annealed ]
120hat 735C
• o.,,x,o"cm
2/,ca7 7 +2,5hat 1220C
O)
o.o
o.s
1.o
1.5
2.0
2.5
3.0
+2.5hat 1270'C ]
phonon energy [meV] Fig. 2. Stress dependence of the phonon transmission through a G e : O sample with high concentration of thermal donors ([TD]=3.Sx 1022 m-3). Under stress various resonances of the interstitial oxygen become visible. The small SNR is due to poor quality of the detector junction [21]. range and thus should be observable as distinct phonon scattering resonances. Instead, we find for higher TD concentrations in Ge a broad, nearly unstructured phonon scattering below about 2.2 meV the details varying somewhat from sample to sample. In some cases a depression of the transmission around 2 meV can be distinguished. In any case the additional scattering is reduced (not shifted) by uniaxial stress. Fig. 2 shows an example for very high concentration of TD. Experiments with specific annealing procedures, counterdoping for compensation, together with comparative IR-measurements are planned to clarify whether the scattering is due to motional or electronic resonances or to a combination of both in the case of a Jahn-Teller effect and to which extent oxygen-related precipitates may be involved. Annealing oxygen-doped silicon at temperatures above about 500°C leads to various types of oxygen-related precipitates with dimensions down to several nanometers. So, phonon scattering might be expected due to geometrical resonances similar to previous observations of Ca clusters in irradiated CaF2 [17]. First experiments show that there is in fact additional phonon scattering due to oxygen precipitation and that there are distinct differences for carbon-lean and carbon-rich material. In the first case the scattering is mainly inelastic indicative of amorphous SiO2 clusters, whereas in the latter case the scattering is mainly elastic and after annealing above 1220°C an extra scattering around 400 GHz is found corresponding to a wavelength of about 10 nm of
I
I
0
I
400
I
I
800
1200
phonon frequency [GHz] Fig. 3. Change ofphonon transmission spectra of carbon-rich Cz-Si with annealing. A line at 330 GHz, correlated with a C-O-complex, vanishes by annealing at 735°C. Additional scattering around 400 GHz appears after annealing 1220°C. Annealing at 1270°C dissolves and perhaps sharpens the distribution [22]. the transverse phonons. Gupta et al. [18] concluded from small angle neutron scattering in carbon-rich material on spherical precipitates of about 9 nm diameter after annealing at 720°C which consist partially of [3-SIC. An example for phonon transmission spectra is given in Fig. 3.
3. Conclusion
From the foregoing it is evident that high-resolution wideband tunable phonon spectroscopy with superconducting tunnel junctions can contribute much to the understanding of oxygen defects in silicon and germanium and possibly so also in other semiconductors such as GaAs [ 19] or GaP.
Acknowledgements
The work reviewed here is an outcome of the activities of quite a group at Stuttgart University. I should like to name M. Welte, W. Forkel, E. Dittrich, W. Scheitler,
K. Laflmann/ Physica B 219&220 (1996) 730 733 M. Gienger, C. Wurster, M. Glaser, G. Schrag, F. Zeller, and, with his steady creative and experienced involvement, W. Eisenmenger. We profited from helpful discussions with H. YamadaKaneta concerning the level sequence in G e : Oi. We are indepted to E.E. Haller, W. Kaiser, and W. Zulehner for the kind supply of appropriate samples. Most of the research reported here has been financially supported by the Deutsche Forschungsgemeinschaft which is gratefully acknowledged.
References [1 ] W. Eisenmenger, in: Physical Acoustics 12, eds. W.P. Mason and R.N. Thurston (Academic Press, New York, 1976) p. 79 [2] C. Wurster, E. Dinrich, W. Scheitler, K. LaBmann, W. Eisenmenger and W. Zulehner, Physica B 219&220 (1996) 763. [3] F. Shimura (ed.), Oxygen in Silicon, in: Semiconductors and Semimetals, Vol. 42, eds. R.K. Willardson, A.C. Beer and E.R. Weber (1994). [4] D.R. Bosomworth, W. Hayes, A.R.L. Spray and G.D. Watkins, Proc. Roy. Soc. Lond. A 317 (1970) 133. [5] C. Kaneta, H. Yamada-Kaneta and A. Ohsawa, Mat. Sci. Forum 38-41 (1989) 323. [6] A. Liz6n-NordstrSm and F. YndurS.in, Solid State Commun. 89 (1994) 819. [7] E. Dittrich, W. Scheitler and W. Eisenmenger, Jpn J. Appl. Phys. 39 (Suppl. 26-3) (1987) 873.
733
[8] U. Werling and K.F. Renk, Phys. Rev. B 39 (1989) 1286. [9] A.A. Volkov, Yu.G. Goncharov, V.P. Kalinushkin, G.V. Kozlov and A. M. Prokhorov, Fiz. Tverd. Tela 31 (1989) 262 [Sov. Phys. Solid State 31 (1989) 1249]. [10] W. Forkel, Thesis, Stuttgart (1977). [11] B. Pajot and P. Clauws, in: Proc. 18th Int. Conf. on Phys. of Semic., Stockholm, 1986, Vol. 2 (World Scientific, Singapore, 1987) p. 911. [12] M. Gienger, M. Glaser and K. LaBmann, Solid State Commun. 86 (1993) 285. [13] H. Yamada-Kaneta, C. Kaneta and T. Ogawa, Phys. Rev, B 42 (1990) 9650. [14] E. Artacho and F. Yndurfiin, in: Proc. 18th Int. Conf. on Defects in Semiconductors, Sendai, 1995 (Trans Tech Publications, Switzerland), to be published. [15] M. Gienger, P. GroB and K. Lal3mann, Phys. Rev. Lett. 64 (1990) 1138. [16] P. Clauws and J. Vennik, Mater. Sci. Forum 10-12 (1986) 941. [17] C. Wurster, K. Lal3mann and W. Eisenmenger, Phys. Rev. Lett. 70 (1993) 3451. [18] S. Gupta, S. Messolares, J.R. Schneider, R.J. Stewart and W. Zulehner, Semicond. Sci. Technol. 7 (1992) 6. [19] F. Maier, R. Eilenberger, W. Beck and K. LaBmann, in: Proc. 18th Int. Conf. on Defects in Semiconductors, Sendai, 1995 (Trans Tech Publications, Switzerland), to be published. [20] E. Dittrich, Thesis, Stuttgart (1989). [21] F. Zeller, Diplomarbeit, Stuttgart (1994). [22] G. Schrag, Diplomarbeit, Stuttgart (1993).