- Email: [email protected]
Complex nature of the copper acceptor in gallium arsenide
Solid State Communications,
Vol. 9, pp. 2281—2284, 1971.
Pergamon Press.
Printed in Great Britain
COMPLEX NATURE OF THE COPPER ACCEPTOR IN GALLIUM ARSENIDE F. Willmann,* M. Blätte,* H.J. Queisser,* and
J.
Treuscht
Physikalisches Institut der Universität Frankfurt, Frankfurt am Main, Germany
(Received 9 September 1971 by E. Moliwo)
The infrared excitation spectrum of the hole bound to the 0.15 eV Cu-acceptor in GaAs has been measured. A novel fine structure has been resolved which is explained by zero-field splitting. It shows that this acceptor has a symmetry lower than Td of the host lattice and cannot be described by a simple substitutional Cu -ion on a Ga site, as heretofore assumed.
MOST DONORS and acceptors in semiconductors
accepted model of a substitutional Cu -ion on a gallium site needs revision.
appear to be adequately described by the elementary model of a substitution of one host atom by the impurity without breaking the symmetry of the host lattice nor evoking formation of other point defects in the vicinity. Recently, however, there has been increasing circumstantial evidence suggesting more complicated structures with reduced symmetries and complex formations. For example, the evidence from diffusion data in Si 1,2 implies dopant-vacancy aggregates. lnterpretations of local vibrational modes in GaAs seem to require more intricate models that that of a simple substitutional dopant. ~ The Jahn—Teller effect and its consequences for impurities in semiconductors has recently been discussed.
Copper in GaAs has been extensively investi5-. 10 gated. Complicated defect reactions involving Cu have been discussed, which affect electrical and optical properties and result in technological consequences. Hall effect and other electrical measurements and photoluminescence studies8 led to the assignment of 0.15eV for the singly charged acceptor level of an assumed substitutional Cu -ion on a Ga site. Luminescence decay of bound excitons has indicated the presence of some copper-induced, but as yet unidentified, species 9 • 10 with C 2~ and C3~symmetries.
4
The investigated samples were prepared by
This letter presents the first direct evidence by infrared absorption for the complex nature of one and well identified GaAs. The specific familiar Cu-acceptor at 0.15 acceptor eV aboveinthe valence band is demonstrated here to have symmetry lower than Td of its host zincblende lattice. The excited hole states are found to be split without external fields, showing that the generally *
diffusion of Cu from an evaporated layer on high purity GaAs crystals in the extrinsic temperature 5 Sufficiently low range to yield the 0.15eV level. doping was achieved to minimize correlation- and pairing effects. The surfaces were lapped and chemically polished to remove at least several microns. Hall effect measurements were performed between 77K and 450K. The fit according to equation (322.14) of reference 11 yields the total carrier concentration NA —ND and confirms the thermal 6 activation energy. We performed the infrared investigations with a high resolution
Present address: Max-Planck-Institut für Festkörperforschung, Stuttgart 1, Germany.
t Present address: Iristitut für Physik, Universität
Dortmund, Germany.
transmission apparatus.
2281
12
The slices of nearly
2282
THE COPPER ACCEPTOR IN GALLIUM ARSENIDE
98
8
-
100
—
GaAs Cu
---
GaAs:Mn
102
The interpretation of acceptor spectra can be based on the work by Mendelson and James (MJ)
706
10 ‘
originally applied to Ge. ‘~ Introducing the appropriate hole mass and static dielectric constant of ‘5
GaAs,
~‘
a
one concludes that the energy separations
between excited states of acceptors in GaAs should be larger by a factor 2.73 than for the corre-
-- -
-
6 -
U,
___________________________________________ 746
Vol. 9, No. 24
148 150 152 P~OT0N ENERGY IN ‘4/Li/ELECTRON VOLT
FIG. 1. Absorption spectrum of GaAs : Cu (solid line, left hand and lower scales), the sample having concentrations \.~ = 1.6 10 7 acceptors/cm~ and \~ = 2.5 10~donors/cm~. The dashed line (right and upper scales) represents the spectrum 3of and GaAs with10 \.~ donors/cm = 9 > io~ ND : Mn = 3 ~. acceptors/cm
1 mm thickness were mounted on a shielded cold finger generating temperatures as low as 6K. We have directly observed the optical cxcitation of the hole bound to the 0.15eV acceptor. Figure 1 presents the absorption coefficient in the range of 146 meV to 155 meV of incident photon energies (solid line). The spectrum reveals two symmetrical lines, termed 1 and 2 henceforth, at 150.4meV and 151.2meV and a strongly asymmetrical line 3 with the maximum at 152.5meV having a slight shoulder on the low energy side. The relative intensities of the lines as well as the linewidths remain approximately constant up to temperatures of about 15K, above this value the lines fade out. This temperature behavior proves that we are dealing with the photoexcitation of bound holes. Local modes would 3 show a different temperature dependence.
mately verify this scaling law in the case of sponding states in Ge. Experimental data approxiGaAs: Mn ‘~ an~on another shallow acceptor in the same material. However, in contrast to the data mentioned above the excited states spectrum of GaAs: Cu shows rather significant deviations from this model. These deviations are a splitting of lines and lower linewidths. In the following we interpret the Cu-lines with the theory by MJ and further explain the splitting. The increased ionization energy of GaAs: Cu (0.15eV) as compared to GaAs:Mn (0.11eV) drastically decreases the transition probabilities to excited states in GaAs: Cu. ~ 18 Therefore the states (8
—
01) and (8
1) in the notation of MJ
are not resolvable for GaAs: Cu as they were in GaAs: Mn and in reference 16. If we assign lines 1 and 3 to states (8 — 02) and (8 — 11) we arirve at an inoization energy
E
4 = 0.156eV and have close agreement with the expected scaling law, the energy separations being 2.8 times ‘4 larger than for the corresponding sattes in Ge.
Line 2 and the strong asymmetry of line 3, which cannot be explained by contributions of the next higher excited states alone, must be caused by the particular nature of the Cu-center in GaAs. The investi~ations on bound exciton spectra of Gross et a]. had indicated that Cu induces some centers in GaAs which behave like complexes consisting of Cu and lattice defects. Lifting the ‘orientational’ degenerac~ by uniaxial stress results of two exciton lines and led in to aansplitting assumption of bound two types of complexes with symmetries C 2v and C3 ~. Safarov 10
Figure 1 contains in addition the excited states spectrum of GaAs : Mn (dashed line) for comparison. The excitation spectrum of GaAs: Mn ‘3 was first reported by Chapman and Hutchinson. Our measurements show nearly the same results, however, the use of higher purity crystals allowed us to detect3 also the so-called ‘B’-resonance at 105.8meV.’
et a]. demonstrated that the trigonal center possesses a larger diffusion coefficient than the orthorhombic one. However, since these investigations were performed on bound excitons, no direct information could be extracted concerning the energy levels of the binding center. Our diffusion and preparation techniques strongly the formation of the trigonal Cu-center in favored
Vol. 9, No. 24
THE COPPER ACCEPTOR IN GALLIUM ARSENIDE
accordance with photoluminescence measurements on the same crystals which show only the trigonal ‘C’-lines of reference 9. Therefore we can now explain the structure of the Cu-acceptor spectrum in Fig. 1 as a consequence of zero-field splitting of excited states by reducing the host lattice symmetry T~ to the trigonal symmetry C3 v. Since no thermalization effects state have splitting been observed, canwith exclude a ground and areweleft a splitting of the p-type envelope of the excited states. From group-theoretical compatibilities we conclude
that the representation l~in
Td
factorizes to
-f F3 in C2 ~., i.e. the p-envelope is split into a singlet and a doublet component transforming as p~and (p~~pp), respectively, where z means the direction 9 of the threefold rotation axis of the center.’
Thus our final assignment is the following: lines 1 (doublet) and 2 (singlet) correspond to the state (8 — 02), the asymmetric line 3 in a superposition of the doublet and singlet belonging to state (8 — 11), the value of the splitting being 0.80 meV. Higher excited states which should be situated above 153.4 meV probably give a small contribution to the high energy tail of line 3. The slight shoulder at 151.9 me\’. which was well meproducible, is assigned to state (7 — 0) in agreement with the conclusions of MJ concerning its energy. Taking now the center of gravity of lines 1 and 2 and of the asymmetric line 3 to recalculate the ionization energy we obtain once more = 0.156eV, but the scaling factor is reduced to 2.7. Not only the splitting of the lines but also the small liriewidths are a consequence of the complex nature of this Cu-acceptor. A resonant
2283
vibrational mode at 3.6 meV has been re~ortedby 9 for the copper C Gross et al. 3~,-center, 0 while Mn on a Ga site couples to the acoustical lattice modes. Therefore, at the temperatures of 6K, the acceptor-phonon scattering is frozen out in the case of GaAs: Cu is contrast to the case of GaAs: Mn. Thus the small linewidths found for excited states absorption in GaAs : Cu reinforce the conclusions that a resonant mode9 of the C3 ~.-copper complex in GaAs exists. In conclusion we have succeeded to identify the familiar 0.156eV Cu-acceptor to be a complex with symmetry C 3 ,~. The evidence is deduced from the zero-field line splitting observed in the infrared. Thus we have presented one example where the previously accepted model of a substitutional acceptorevidence must be from abandoned account ofspectra. direct optical infraredonexcitation
It is hoped that these results together with similar optical investigations will contribute towards resolving not only the still complicated defect reactions in GaAs but in other semiconductor-impurity systems as well. In the case of GaAs : Cu further details should be obtained from optical measurements with applied stress and magnetic fields. Such experiments are presently in preparation. .icknowledgements — We are grateful to Dr. Schairer for supplying the photoluminescence measurements and for helpful discussions and to P. Hiesinger for performing the Hall data. The financial support of the Deutsche Forschungsgemeirischaft and the Fraunhofer Gesellschaft is greatly appreciated. This work is a part of a proiect of the ‘Sonderforschungsbereich Festkdrperspektroskopie Darmstadt-Frankfurt’.
REFERENCES
1.
GHOSHTAGORE R.N., P/iv~.R’v. Len. 25, 856 (1970); Pl~v,’~. Rev, 83, 389 and 379 (1971).
2. 3.
SEEGER A. and CHIN K.P.. Pins. Status Saudi 29, 455 (1968). SPITZER W. G., FestkPrperprohlen?e \‘ol XI, Pergamon—Vieweg (1971).
4.
MORGAN T.N., Pins. Re v. Len. 24. 887 (1970).
5.
HALL R.N. and RACETTE J.H., J. app!. Phys. 35, 379 (1964).
2284
THE COPPER ACCEPTOR IN GALLIUM ARSENIDE
Vol. 9, No. 24
6.
FULLER C.S., WOLFSTIRN K.B. and ALLISON H.W., J. appi. Phys. 38, 2873 (1967).
7.
BRODOVOI V.A. and KOLESNIK N.!., Soviet Phys.-Semicond. 4, 1770 (1971).
8.
QUEJSSER H.J. and FULLER C.S., J. app!. Phys. 37, 4895 (1966).
9.
GROSS E.F., SAFAROV V.1., SEDOV V.E. and MARUSHCHAK V.A., Soviet Phi s.-Solid State 11,
10.
277 (1969). SAFAROV V.!., SEDOV V.E. and YUGOVA T.G., Soviet Phys.-Semicond. 4, 119 (1970).
11.
BLAKEMORE J.S., Semiconductor Statistics p. 139, Pergamon Press, New York (1962).
12.
BLATTE M., thesis, Universitüt Frankfurt am Main, Germany, 1970 (unpublished).
13.
CHAPMAN R.A. and HUTCHINSON W.G., Phys. Rev. Leit. 18, 443 (1967).
14.
MENDELSON K.S. and JAMES H.M.,
J.
Phys. Chern. Solids 24, 729 (1964).
15.
MEARS A.L. and STRADLING R.A.,
J.
Phys. C4, L22 (1971).
16.
SCHAIRER W. and YEP T.O., Solid State Common. 9, 421 (1971).
17.
On the basis of the Quantum Defect Method as described by BEBB H.B., Phys. Rev. 185, 1116 (1969); BEBB H.B. and CHAPMAN R.A., Solid State Commun. 7, no. 11, 5—2:1 pp. (June 1969) (Proc. of the Third mt. Conf. on Photoconducizvitv, Standford, 12—25 Aug 1969), the optical matrix elements of transitions between s-like ground state and p-like excited states decrease with increasing ionization energy as is clearly seen in Fig. 1.
18.
The continuum absorption will be discussed elsewhere.
19.
This is in contrast to the case of the orthorhombic center, where a splitting into three components would be detected.
20.
SCHAIRER W., in a private communication, suggests that the resonant mode may account for the asymmetric shape of the Cu-luminescence line, as observed in reference 8. Such an asymmetry has not been observed in the cased of Mn by LEE T.C. and ANDERSON W.W., Solid State Corn,nuii. 2, 265 (1964) and of Sn in GaAs by SCHAIRER W. and GROBE E., Solid State Commii,~.8, 2017 (1970).
Das infrarote Anregurigsspektrum des am 0.15 eV Kupfer-Akzeptor in GaAs gebundenen Defektelektrons wurde gemessen. Eine neuartige Feinstruktur wird als Aufspaltung ohne ~uBere Felder interpretiert. Sic zeigt, dali dieser Kupfer-Akzeptor eine gegenüber T~ des Wirtsgitters emniedrigte Symmetric besitzt und nicht mehr als substitutionelles Cu -Ion auf einem Ga-Platz beschrieben werden kann. wie es bisher angenommen wurde.
Vol. 9, pp. 2281—2284, 1971.
Pergamon Press.
Printed in Great Britain
COMPLEX NATURE OF THE COPPER ACCEPTOR IN GALLIUM ARSENIDE F. Willmann,* M. Blätte,* H.J. Queisser,* and
J.
Treuscht
Physikalisches Institut der Universität Frankfurt, Frankfurt am Main, Germany
(Received 9 September 1971 by E. Moliwo)
The infrared excitation spectrum of the hole bound to the 0.15 eV Cu-acceptor in GaAs has been measured. A novel fine structure has been resolved which is explained by zero-field splitting. It shows that this acceptor has a symmetry lower than Td of the host lattice and cannot be described by a simple substitutional Cu -ion on a Ga site, as heretofore assumed.
MOST DONORS and acceptors in semiconductors
accepted model of a substitutional Cu -ion on a gallium site needs revision.
appear to be adequately described by the elementary model of a substitution of one host atom by the impurity without breaking the symmetry of the host lattice nor evoking formation of other point defects in the vicinity. Recently, however, there has been increasing circumstantial evidence suggesting more complicated structures with reduced symmetries and complex formations. For example, the evidence from diffusion data in Si 1,2 implies dopant-vacancy aggregates. lnterpretations of local vibrational modes in GaAs seem to require more intricate models that that of a simple substitutional dopant. ~ The Jahn—Teller effect and its consequences for impurities in semiconductors has recently been discussed.
Copper in GaAs has been extensively investi5-. 10 gated. Complicated defect reactions involving Cu have been discussed, which affect electrical and optical properties and result in technological consequences. Hall effect and other electrical measurements and photoluminescence studies8 led to the assignment of 0.15eV for the singly charged acceptor level of an assumed substitutional Cu -ion on a Ga site. Luminescence decay of bound excitons has indicated the presence of some copper-induced, but as yet unidentified, species 9 • 10 with C 2~ and C3~symmetries.
4
The investigated samples were prepared by
This letter presents the first direct evidence by infrared absorption for the complex nature of one and well identified GaAs. The specific familiar Cu-acceptor at 0.15 acceptor eV aboveinthe valence band is demonstrated here to have symmetry lower than Td of its host zincblende lattice. The excited hole states are found to be split without external fields, showing that the generally *
diffusion of Cu from an evaporated layer on high purity GaAs crystals in the extrinsic temperature 5 Sufficiently low range to yield the 0.15eV level. doping was achieved to minimize correlation- and pairing effects. The surfaces were lapped and chemically polished to remove at least several microns. Hall effect measurements were performed between 77K and 450K. The fit according to equation (322.14) of reference 11 yields the total carrier concentration NA —ND and confirms the thermal 6 activation energy. We performed the infrared investigations with a high resolution
Present address: Max-Planck-Institut für Festkörperforschung, Stuttgart 1, Germany.
t Present address: Iristitut für Physik, Universität
Dortmund, Germany.
transmission apparatus.
2281
12
The slices of nearly
2282
THE COPPER ACCEPTOR IN GALLIUM ARSENIDE
98
8
-
100
—
GaAs Cu
---
GaAs:Mn
102
The interpretation of acceptor spectra can be based on the work by Mendelson and James (MJ)
706
10 ‘
originally applied to Ge. ‘~ Introducing the appropriate hole mass and static dielectric constant of ‘5
GaAs,
~‘
a
one concludes that the energy separations
between excited states of acceptors in GaAs should be larger by a factor 2.73 than for the corre-
-- -
-
6 -
U,
___________________________________________ 746
Vol. 9, No. 24
148 150 152 P~OT0N ENERGY IN ‘4/Li/ELECTRON VOLT
FIG. 1. Absorption spectrum of GaAs : Cu (solid line, left hand and lower scales), the sample having concentrations \.~ = 1.6 10 7 acceptors/cm~ and \~ = 2.5 10~donors/cm~. The dashed line (right and upper scales) represents the spectrum 3of and GaAs with10 \.~ donors/cm = 9 > io~ ND : Mn = 3 ~. acceptors/cm
1 mm thickness were mounted on a shielded cold finger generating temperatures as low as 6K. We have directly observed the optical cxcitation of the hole bound to the 0.15eV acceptor. Figure 1 presents the absorption coefficient in the range of 146 meV to 155 meV of incident photon energies (solid line). The spectrum reveals two symmetrical lines, termed 1 and 2 henceforth, at 150.4meV and 151.2meV and a strongly asymmetrical line 3 with the maximum at 152.5meV having a slight shoulder on the low energy side. The relative intensities of the lines as well as the linewidths remain approximately constant up to temperatures of about 15K, above this value the lines fade out. This temperature behavior proves that we are dealing with the photoexcitation of bound holes. Local modes would 3 show a different temperature dependence.
mately verify this scaling law in the case of sponding states in Ge. Experimental data approxiGaAs: Mn ‘~ an~on another shallow acceptor in the same material. However, in contrast to the data mentioned above the excited states spectrum of GaAs: Cu shows rather significant deviations from this model. These deviations are a splitting of lines and lower linewidths. In the following we interpret the Cu-lines with the theory by MJ and further explain the splitting. The increased ionization energy of GaAs: Cu (0.15eV) as compared to GaAs:Mn (0.11eV) drastically decreases the transition probabilities to excited states in GaAs: Cu. ~ 18 Therefore the states (8
—
01) and (8
1) in the notation of MJ
are not resolvable for GaAs: Cu as they were in GaAs: Mn and in reference 16. If we assign lines 1 and 3 to states (8 — 02) and (8 — 11) we arirve at an inoization energy
E
4 = 0.156eV and have close agreement with the expected scaling law, the energy separations being 2.8 times ‘4 larger than for the corresponding sattes in Ge.
Line 2 and the strong asymmetry of line 3, which cannot be explained by contributions of the next higher excited states alone, must be caused by the particular nature of the Cu-center in GaAs. The investi~ations on bound exciton spectra of Gross et a]. had indicated that Cu induces some centers in GaAs which behave like complexes consisting of Cu and lattice defects. Lifting the ‘orientational’ degenerac~ by uniaxial stress results of two exciton lines and led in to aansplitting assumption of bound two types of complexes with symmetries C 2v and C3 ~. Safarov 10
Figure 1 contains in addition the excited states spectrum of GaAs : Mn (dashed line) for comparison. The excitation spectrum of GaAs: Mn ‘3 was first reported by Chapman and Hutchinson. Our measurements show nearly the same results, however, the use of higher purity crystals allowed us to detect3 also the so-called ‘B’-resonance at 105.8meV.’
et a]. demonstrated that the trigonal center possesses a larger diffusion coefficient than the orthorhombic one. However, since these investigations were performed on bound excitons, no direct information could be extracted concerning the energy levels of the binding center. Our diffusion and preparation techniques strongly the formation of the trigonal Cu-center in favored
Vol. 9, No. 24
THE COPPER ACCEPTOR IN GALLIUM ARSENIDE
accordance with photoluminescence measurements on the same crystals which show only the trigonal ‘C’-lines of reference 9. Therefore we can now explain the structure of the Cu-acceptor spectrum in Fig. 1 as a consequence of zero-field splitting of excited states by reducing the host lattice symmetry T~ to the trigonal symmetry C3 v. Since no thermalization effects state have splitting been observed, canwith exclude a ground and areweleft a splitting of the p-type envelope of the excited states. From group-theoretical compatibilities we conclude
that the representation l~in
Td
factorizes to
-f F3 in C2 ~., i.e. the p-envelope is split into a singlet and a doublet component transforming as p~and (p~~pp), respectively, where z means the direction 9 of the threefold rotation axis of the center.’
Thus our final assignment is the following: lines 1 (doublet) and 2 (singlet) correspond to the state (8 — 02), the asymmetric line 3 in a superposition of the doublet and singlet belonging to state (8 — 11), the value of the splitting being 0.80 meV. Higher excited states which should be situated above 153.4 meV probably give a small contribution to the high energy tail of line 3. The slight shoulder at 151.9 me\’. which was well meproducible, is assigned to state (7 — 0) in agreement with the conclusions of MJ concerning its energy. Taking now the center of gravity of lines 1 and 2 and of the asymmetric line 3 to recalculate the ionization energy we obtain once more = 0.156eV, but the scaling factor is reduced to 2.7. Not only the splitting of the lines but also the small liriewidths are a consequence of the complex nature of this Cu-acceptor. A resonant
2283
vibrational mode at 3.6 meV has been re~ortedby 9 for the copper C Gross et al. 3~,-center, 0 while Mn on a Ga site couples to the acoustical lattice modes. Therefore, at the temperatures of 6K, the acceptor-phonon scattering is frozen out in the case of GaAs: Cu is contrast to the case of GaAs: Mn. Thus the small linewidths found for excited states absorption in GaAs : Cu reinforce the conclusions that a resonant mode9 of the C3 ~.-copper complex in GaAs exists. In conclusion we have succeeded to identify the familiar 0.156eV Cu-acceptor to be a complex with symmetry C 3 ,~. The evidence is deduced from the zero-field line splitting observed in the infrared. Thus we have presented one example where the previously accepted model of a substitutional acceptorevidence must be from abandoned account ofspectra. direct optical infraredonexcitation
It is hoped that these results together with similar optical investigations will contribute towards resolving not only the still complicated defect reactions in GaAs but in other semiconductor-impurity systems as well. In the case of GaAs : Cu further details should be obtained from optical measurements with applied stress and magnetic fields. Such experiments are presently in preparation. .icknowledgements — We are grateful to Dr. Schairer for supplying the photoluminescence measurements and for helpful discussions and to P. Hiesinger for performing the Hall data. The financial support of the Deutsche Forschungsgemeirischaft and the Fraunhofer Gesellschaft is greatly appreciated. This work is a part of a proiect of the ‘Sonderforschungsbereich Festkdrperspektroskopie Darmstadt-Frankfurt’.
REFERENCES
1.
GHOSHTAGORE R.N., P/iv~.R’v. Len. 25, 856 (1970); Pl~v,’~. Rev, 83, 389 and 379 (1971).
2. 3.
SEEGER A. and CHIN K.P.. Pins. Status Saudi 29, 455 (1968). SPITZER W. G., FestkPrperprohlen?e \‘ol XI, Pergamon—Vieweg (1971).
4.
MORGAN T.N., Pins. Re v. Len. 24. 887 (1970).
5.
HALL R.N. and RACETTE J.H., J. app!. Phys. 35, 379 (1964).
2284
THE COPPER ACCEPTOR IN GALLIUM ARSENIDE
Vol. 9, No. 24
6.
FULLER C.S., WOLFSTIRN K.B. and ALLISON H.W., J. appi. Phys. 38, 2873 (1967).
7.
BRODOVOI V.A. and KOLESNIK N.!., Soviet Phys.-Semicond. 4, 1770 (1971).
8.
QUEJSSER H.J. and FULLER C.S., J. app!. Phys. 37, 4895 (1966).
9.
GROSS E.F., SAFAROV V.1., SEDOV V.E. and MARUSHCHAK V.A., Soviet Phi s.-Solid State 11,
10.
277 (1969). SAFAROV V.!., SEDOV V.E. and YUGOVA T.G., Soviet Phys.-Semicond. 4, 119 (1970).
11.
BLAKEMORE J.S., Semiconductor Statistics p. 139, Pergamon Press, New York (1962).
12.
BLATTE M., thesis, Universitüt Frankfurt am Main, Germany, 1970 (unpublished).
13.
CHAPMAN R.A. and HUTCHINSON W.G., Phys. Rev. Leit. 18, 443 (1967).
14.
MENDELSON K.S. and JAMES H.M.,
J.
Phys. Chern. Solids 24, 729 (1964).
15.
MEARS A.L. and STRADLING R.A.,
J.
Phys. C4, L22 (1971).
16.
SCHAIRER W. and YEP T.O., Solid State Common. 9, 421 (1971).
17.
On the basis of the Quantum Defect Method as described by BEBB H.B., Phys. Rev. 185, 1116 (1969); BEBB H.B. and CHAPMAN R.A., Solid State Commun. 7, no. 11, 5—2:1 pp. (June 1969) (Proc. of the Third mt. Conf. on Photoconducizvitv, Standford, 12—25 Aug 1969), the optical matrix elements of transitions between s-like ground state and p-like excited states decrease with increasing ionization energy as is clearly seen in Fig. 1.
18.
The continuum absorption will be discussed elsewhere.
19.
This is in contrast to the case of the orthorhombic center, where a splitting into three components would be detected.
20.
SCHAIRER W., in a private communication, suggests that the resonant mode may account for the asymmetric shape of the Cu-luminescence line, as observed in reference 8. Such an asymmetry has not been observed in the cased of Mn by LEE T.C. and ANDERSON W.W., Solid State Corn,nuii. 2, 265 (1964) and of Sn in GaAs by SCHAIRER W. and GROBE E., Solid State Commii,~.8, 2017 (1970).
Das infrarote Anregurigsspektrum des am 0.15 eV Kupfer-Akzeptor in GaAs gebundenen Defektelektrons wurde gemessen. Eine neuartige Feinstruktur wird als Aufspaltung ohne ~uBere Felder interpretiert. Sic zeigt, dali dieser Kupfer-Akzeptor eine gegenüber T~ des Wirtsgitters emniedrigte Symmetric besitzt und nicht mehr als substitutionelles Cu -Ion auf einem Ga-Platz beschrieben werden kann. wie es bisher angenommen wurde.