- Email: [email protected]
Optical properties of a ‘quasi-disordered’ semiconductor: ZnIn2S4
Solid State Communications,
Vol. 13, pp. 1805—1809, 1973.
Pergamon Press.
Printed in Great Britain
OPTICAL PROPERTIES OF A ‘QUASI-DISORDERED’ SEMICONDUCTOR: ZnIn2 S4 A. Bosacchi, B. Bosacchi,* S. Franchi and L. Hernandezt Laboratorio MASPEC del CNR, Parma, Italy
(Received 31 July 1973 by R. Fieschi)
Optical absorption and thermoluminescence measurements have been performed on single crystals of ZnIn2 S4. An absorption edge and a distribution of traps which depend exponentially on the radiation energy with the same ‘slope’, have been found. These results provide evidence for the existence of a considerable amount of intrinsic disorder in this compound, and allow one to relate the discussion to the wider problem of the optical properties of amorphous semiconductors. I
THE ELECTRONIC properties of disordered semiconductors present the subject of of strong 1 ‘are In at this connection a group crystals, interest.has not been much investigated so far, acquires which a particular relevance; they are the ternary compounds of the type AB 2~is Zn, Cd, or Hg, B3~ 2X,, (where A is Al, Ga, or In, and X2 is 5, Se, or Te), in most
I
E .~.
10’
-
4 /7
I.-
z
cation of which sites) a large is present number in of stoichiometric vacancies (1/4 conditions.5 of the In view of this intrinsic disorder, these crystals may
w
be considered as intermediate structures between
E
~1
U
z 0
amorphous and crystalline semiconductors,6 and their study can provide effects. useful information on the disorder The presence of such a large concentration of intrinsic defects is expected to influence strongly the optical properties in the region of the absorption edge; in this communication we present some experimental evidence, concerning single crystals of ZnIn 2S4, which confirms this viewpoint. ZnIn2S4 crystallizes in the rhomboedral structure with space group C~(R3m),and may be thought as a series of *
I
-
I/i
// / / p1,7 / I
U, 4
102 .
_~ ~_
~hIi / /,~ /
2~
I 2.5
xlO
2.7
2.9
3.1
PHOTON ENERGY 1eV)
FIG. 1. Optical absorption coefficient for four values of the temperature (a = 77°K,b = 180°K,c = 250°K, d = 300°K).The dashed curve represents the absorption coefficient after the correction for reflection losses on the measured absorption (continuous curve).
Istituto de Fisica dell’Università di Parma, Italy and Gruppo Nazionale di Struttura della Materia del CNR, Italy.
t Istituto di Fisica dell’Universitàdi Parma, Italy
layers with strong In—S and Zn—S bonds in the layers, 7 and weak S—S bonds between them.
and Instituto de Fisica de laUniversidad de la Habana, Cuba. 1805
1806
OPTICAL PROPERTIESOF ZnIn2S4
Vol. 13, No. 11
The optical absorption coefficient of ZnIn2 S4 at four different temperatures, obtained through a study 8 of athe transmission, for reflection in series of plateletscorrected whose thickness rangedlosses, from 2.3 pm to 78 pm, is reported in Fig. 1. These results, which extend previous measurements by some of us,9 are also in agreement with those ofShionoya and Ebina.’°Their main features can be summarized as follows:
exponential tail in the absorption edge, and its ternperature independence, which are often in the amorphous semiconductors,16 canfound in factalso be well explained with a mechanism in which either the localised levels provide directly the states for the optical transitions,17’ 18 or create strong electric fields in which the transitions take place,12’16”9 The disorder associated with these levels would also account for the absence of any excitonic peak,~yet
(a) the absorption coefficient varies exponentially with the energy of the radiation over a large range (20 cnf1 ~ a ~ 1. l0~cm1). Below 20 cm~our results are no more reliable, since the appaient absorption is completely caused by reflection losses, (b) the exponential decay of the absorption is independent on the temperature over the whole range investigated (77°K< T< 300°K)and its ‘slope’ is 165 ±5 meV/decade.
allowing a crystalline behavior at high values of the absorption constant,~’22The assumption of a large number of electronic states in the gap is also supported by the strong phosphorescence, the long decay-time of photoconductivity, and several other effects on which we shall report elsewhere.23 Besides this, we got further experimental evidence for the existence of these states, by performing thermoluminescence (TL) measurements on the same samples used in the absorption experiment.
(c) at high values of the absorption coefficient (a ~ 1. iO~cnf’) the relation a = (E E~)”2fits the experimental values with good accuracy.
t
(d) no evidence of any excitonic structure, in spite of careful search, has been found, even extending the measurements down to 4.2°K.
0~with light of energy close to that of the gap, at a temperature T0 then, after a waiting time &, during which the phosphorescence emission ‘PH was taken, the temperature was raised linearly with time, according to the relation T = T0 + ~3t,and the TL
In our TL runs, the crystal was excited for a time
—
Point (a) is very common in semiconductors, 11’3 Inand ourhas been widely discussed in recent years. case, however, the situation is somewhat different, since point (b) allows us to rule out, among the many mechanisms which have been proposed to explain the exponential behavior, those which involve a temperature dependence. Point (b) is indeed the most striking feature of Fig. 1, being quite exceptional in crystalline semiconductors, where, at our knowledge, it has been found only for some 14 Point (c) ~ strongly compensated compounds. good agreement with the commonly accepted theory of the optical absorption in semiconductors, for the case of direct allowed transitions between the extrema of valence and conduction bands. Point (d), on the contrary, is somewhat surprising, since excitonic effects can be expected in a crystal which should show some similarity with ZnS, and which has a 15 good degree of ionicity. The presence of a large concentration of localized states in the forbidden gap, which is consistent with the defective nature of this compound, provides a unified explanation for all the above points. The
sionas‘FL was recorded. of curves was obtamed, reported in Fig. 2,Aset for differentvalues of the excitation temperature T 0, whereas all the other ex~eimenthlparameters were kept constant (& = 7 mi jl ~ 0.3°Kse~’).The measurements were always performed on the same sample, and care was paid to check that the recycling did not cause any saturation effect on the crystal. For any T01, the corresponding glow-curve is characterized by a single peak at temperature TM~which shifts towards higher temperatures as T~increases. The most obvious explanation of this trend is to admit a continuous distribution of traps. Though we are at present considering the methods of Bube Ct at,” we got an approximate evaluation of the features of the trap distribution through a refinement of an idea of Garlick and Gibson.25 The area enclosed under the curve obtainedwith excitation at To 1 is proportional to the total number of carriers released from the traps during the heating process, when allowance is made for the temperature dependence of the luminescence efficiency. The difference between the areas related to and is therefore proportional to the total number of carriers released from
Vol. 13, No. 11
OPTICAL PROPERTIES OF ZnIn2S4
I
I
I
To1. We can therefore build the curve of the distribution of the filled traps as a function of T01 the relation between To1 and E0, may then be obtained, approximately, with the method of the initial rise;~assuming in the limited range of temperature under investi-
1
20
2
1
-
78 ‘1<
2
-
89 ‘1<
gation, that this relation is linear, got which E~= 2.54 should give we results are T0. This method, which26will be p~esented and discussed in detail elsewhere, approximately independent on the kinetics of the
5 148 01< 67 - 169 190 ‘1< 01<
10
0
processes involved; when applied to the data of Fig. 2, it leads to the curve of Fig. 3, which gives the distribution of the traps, as a function of the energy below the ‘intrinsic’ absorption. This distribution is well approximated by an exponential curve, whose ‘slope’ is 160 ±20 meV/decade. This value has been checked also by analyzing the phosphorescence decay; in the case of an exponential distribution of trape, it is easily shown that Ip~follows, at long times, a power law, from which the value of the exponentail ‘slope’ can be found.27 (This procedure
-
“k
6
150
200
TEMPERATURE (~K)
FIG. 2. Thermoluminescence emission for different values of the excitation temperature. I
100
•\. \
disorder effect causes a broadening of the energy levels. In particular, the exponential distribution of Fig. 3 is consistent with the presence of fluctuations in the crystal potential, caused by structural defects, like vacancies, which give rise not simply to an exponential tail in the absorption, but to real localized states which act as traps for the carriers.
\
\
10
\
2 200
300
can be shown to be independent on the kinetics involved). The results of this analysis (150 ±30 rneV/ decade) are also in agreement with the TL value. A continuous distribution of traps is easily explained in a defective semiconductor, since any
I
\
z
1807
\
\ •\
400 ENERGY (m.V}
500
FiG. 3. Traps distribution vs energy below the intrinsic absorption. the traps enclosed in an energy region ~ where is an energy associated with the temperature —
Both optical and TL measurements, in conclusion, confirm the picture of ZnIn 2 S4 as a quasi-disordered crystal, in which the disorder effects prevail in the region of the absorption edge and below, where the effects of the ‘intrinsic’ structure are weaker or absent. This picture is also consistent, in view of the layer nature of 28 thiswho compound, with theory of has shown thata recent the formation Gubanov, energy for a fluctuation in the crystal potential decreases with the ‘dimensionality’ of the crystal itself. M~interesting point is represented by the closeness
between the values of the slopes of the absorption tail and that of the trap distribution, analoguously to what has been found in As 29 Ifwe assume that 2 S3. the number of filled traps, at any energy, is proportional to the localized states concentration, this
1808
OPTICAL PROPERTIES OF ZnIn2 S4
closeness thatabsorption the localized levelstransitions play directly a relevantsuggests role in the process; between extended and localized states, as responsible for the exponential tail, have often been invoked, but also questioned, in the hterature on the amorphous semiconductor.30 Anyway, the relation itself between the real density of states and the absorption edge tail
Vol. 13, No. 11
21’81 that any definite is so controversial andvery obscure, conclusion would be premature at present. Acknowledgements We thank Dr. Paorici, who grew the samples used m this experiment and Prof. Fieschi for useful discussions. Thanks are also due to Dr. Guzzi for comments on the phosphorescence measurements. —
REFERENCES 1.
MO1’T N.F. and DAVIS E.A. Electronic Processes in Non-Crystalline Solids, Oxford University Press, Oxford (1971).
2.
ADLER D. Amorphous Semiconductors. Butterworths, London (1972).
3.
STUKE J. J. Non-Crystalline Solids 4, 1(1970).
4. 5.
FRITSCHE H. J. Non-Crystalline Solids 6,49(1971). GREENWOOD N~N.Ionic Crystals, Lattice Defects and Nonstoichiometry, Butterworth, London (1968).
6.
RADAUTSAN S.J. Non-Crystalline Solids 4, 370 (1970).
7.
LAPPE F., NIGGLI A., NITSCHE R. and WHITE J.G. Kristall. 117, 146 (1962).
8.
GREENAWAY D.L. and HARBEKE G. Optical Properties and Band Structure ofSemiconductors. Pergamon Press, Oxford (1968). BALDINI G., BOSACCHI A. and FRANCHI S. Rapporto MASPEC No.2 (Dec. 1971).
9. 10.
SHIONOYA S. and EBINA A.J. Phys. Soc. Japan 19, 1150(1964).
11.
HOPFIELD JJ. Comm. Solid State Phys. 1, 16 (1968).
12.
DOW J.D. and REDFIELD D. Phys. Rev. B5, 594 (1972).
13. 14.
BOSACCHI B. and ROBINSON J.E. Solid State Commun. 10, 797 (1972). REDFIELD D. and AFROMOWITZ M.A.Appl. Phys. Lett. 11, 138 (1967).
15. 16.
MANCA P., MUNTONI C., RAGA F. and SPIGA A. Phys. Stat. Sol. (b) 44, 51(1971). See, for example, TAUC J.Mat. Res. Bull. 5,721(1970).
17. 18.
LANYON H.P.D. Phys. Rev. 130, 134 (1963). TAUC J. In Optical Properties ofSolids (edited by Abeles F.) North-Holland (1968).
19. 20. 21.
DAVIS E.A. and MOTT N.F. Phil. Mag. 22, 903 (1970). BONCH-BRUEVICH V.L. and ISKRA V.D., Fiz. Tekh. Poluprov. 5, 1948 (1971) [Soy. Phys. Semicond. 5, 1690 (1972)]. BONCH-BRUEVICH V.L. Phys. Stat. Sol. 42,35 (1970).
22. 23. 24. 25.
ESSER B. Phys. Stat. Sol. (b) 55, 503 (1973). BOSACCHI A., BOSACCHI B., FRANCH1 S. and HERNANDEZ L. to be published. BUBE R.H., DUSSEL G.A., HO C.—T. and MILLER L.D. J. Appi. Phys. 37,21(1966). GARLICK G.FJ. and GIBSON A.F.Proc. Phys. Soc. 60,574(1948).
26. 27.
BOSACCHI A., BOSACCHI B. and FRANCHI S. to be published. RANDALLJ.T. and WILKINS M.H.F. Proc. R. Soc. A 184,390(1945).
28. 29.
GUBANOV A.I. Fiz. Tekh. Poluprov. 6, 1378 (1972) [Soy. Phys. Semicond. 6, 1202(1973)]. ANDRIESH A.M., SHUTOV S.D. and IOVU M.S. Phys. Stat. Sol. (a) 11, K43 (1972).
Vol. 13, No. 11
OPTICAL PROPERTIES OF ZnIn2S4
1809
30.
See, for example, TAUC J. and MENTH A. J. Non-Crystalline Solids 8—10, 569 (1972), and also references 4, 16, 18 and 19.
31.
DOW J.D. and HOPFIELD JJ. J. Non-Crystalline Solids 8—10, 664 (1972).
Nous avons mesuré l’absorption optique et La thermoluminescence des monocristaux de ZnIn2 S4. On a trouvé un c~téd’absorption et une distribution de pièges qul dependent exponentiellement de l’énergie de Ia radiation, avec La méme ‘pente’. Les resultats montrent quil existe une quantité considerable de désordre intrinséque dans cc compose, et nous permettent de relier la discussion au probleme plus vaste des proprietCs optiques des semiconducteurs amorphes.
Vol. 13, pp. 1805—1809, 1973.
Pergamon Press.
Printed in Great Britain
OPTICAL PROPERTIES OF A ‘QUASI-DISORDERED’ SEMICONDUCTOR: ZnIn2 S4 A. Bosacchi, B. Bosacchi,* S. Franchi and L. Hernandezt Laboratorio MASPEC del CNR, Parma, Italy
(Received 31 July 1973 by R. Fieschi)
Optical absorption and thermoluminescence measurements have been performed on single crystals of ZnIn2 S4. An absorption edge and a distribution of traps which depend exponentially on the radiation energy with the same ‘slope’, have been found. These results provide evidence for the existence of a considerable amount of intrinsic disorder in this compound, and allow one to relate the discussion to the wider problem of the optical properties of amorphous semiconductors. I
THE ELECTRONIC properties of disordered semiconductors present the subject of of strong 1 ‘are In at this connection a group crystals, interest.has not been much investigated so far, acquires which a particular relevance; they are the ternary compounds of the type AB 2~is Zn, Cd, or Hg, B3~ 2X,, (where A is Al, Ga, or In, and X2 is 5, Se, or Te), in most
I
E .~.
10’
-
4 /7
I.-
z
cation of which sites) a large is present number in of stoichiometric vacancies (1/4 conditions.5 of the In view of this intrinsic disorder, these crystals may
w
be considered as intermediate structures between
E
~1
U
z 0
amorphous and crystalline semiconductors,6 and their study can provide effects. useful information on the disorder The presence of such a large concentration of intrinsic defects is expected to influence strongly the optical properties in the region of the absorption edge; in this communication we present some experimental evidence, concerning single crystals of ZnIn 2S4, which confirms this viewpoint. ZnIn2S4 crystallizes in the rhomboedral structure with space group C~(R3m),and may be thought as a series of *
I
-
I/i
// / / p1,7 / I
U, 4
102 .
_~ ~_
~hIi / /,~ /
2~
I 2.5
xlO
2.7
2.9
3.1
PHOTON ENERGY 1eV)
FIG. 1. Optical absorption coefficient for four values of the temperature (a = 77°K,b = 180°K,c = 250°K, d = 300°K).The dashed curve represents the absorption coefficient after the correction for reflection losses on the measured absorption (continuous curve).
Istituto de Fisica dell’Università di Parma, Italy and Gruppo Nazionale di Struttura della Materia del CNR, Italy.
t Istituto di Fisica dell’Universitàdi Parma, Italy
layers with strong In—S and Zn—S bonds in the layers, 7 and weak S—S bonds between them.
and Instituto de Fisica de laUniversidad de la Habana, Cuba. 1805
1806
OPTICAL PROPERTIESOF ZnIn2S4
Vol. 13, No. 11
The optical absorption coefficient of ZnIn2 S4 at four different temperatures, obtained through a study 8 of athe transmission, for reflection in series of plateletscorrected whose thickness rangedlosses, from 2.3 pm to 78 pm, is reported in Fig. 1. These results, which extend previous measurements by some of us,9 are also in agreement with those ofShionoya and Ebina.’°Their main features can be summarized as follows:
exponential tail in the absorption edge, and its ternperature independence, which are often in the amorphous semiconductors,16 canfound in factalso be well explained with a mechanism in which either the localised levels provide directly the states for the optical transitions,17’ 18 or create strong electric fields in which the transitions take place,12’16”9 The disorder associated with these levels would also account for the absence of any excitonic peak,~yet
(a) the absorption coefficient varies exponentially with the energy of the radiation over a large range (20 cnf1 ~ a ~ 1. l0~cm1). Below 20 cm~our results are no more reliable, since the appaient absorption is completely caused by reflection losses, (b) the exponential decay of the absorption is independent on the temperature over the whole range investigated (77°K< T< 300°K)and its ‘slope’ is 165 ±5 meV/decade.
allowing a crystalline behavior at high values of the absorption constant,~’22The assumption of a large number of electronic states in the gap is also supported by the strong phosphorescence, the long decay-time of photoconductivity, and several other effects on which we shall report elsewhere.23 Besides this, we got further experimental evidence for the existence of these states, by performing thermoluminescence (TL) measurements on the same samples used in the absorption experiment.
(c) at high values of the absorption coefficient (a ~ 1. iO~cnf’) the relation a = (E E~)”2fits the experimental values with good accuracy.
t
(d) no evidence of any excitonic structure, in spite of careful search, has been found, even extending the measurements down to 4.2°K.
0~with light of energy close to that of the gap, at a temperature T0 then, after a waiting time &, during which the phosphorescence emission ‘PH was taken, the temperature was raised linearly with time, according to the relation T = T0 + ~3t,and the TL
In our TL runs, the crystal was excited for a time
—
Point (a) is very common in semiconductors, 11’3 Inand ourhas been widely discussed in recent years. case, however, the situation is somewhat different, since point (b) allows us to rule out, among the many mechanisms which have been proposed to explain the exponential behavior, those which involve a temperature dependence. Point (b) is indeed the most striking feature of Fig. 1, being quite exceptional in crystalline semiconductors, where, at our knowledge, it has been found only for some 14 Point (c) ~ strongly compensated compounds. good agreement with the commonly accepted theory of the optical absorption in semiconductors, for the case of direct allowed transitions between the extrema of valence and conduction bands. Point (d), on the contrary, is somewhat surprising, since excitonic effects can be expected in a crystal which should show some similarity with ZnS, and which has a 15 good degree of ionicity. The presence of a large concentration of localized states in the forbidden gap, which is consistent with the defective nature of this compound, provides a unified explanation for all the above points. The
sionas‘FL was recorded. of curves was obtamed, reported in Fig. 2,Aset for differentvalues of the excitation temperature T 0, whereas all the other ex~eimenthlparameters were kept constant (& = 7 mi jl ~ 0.3°Kse~’).The measurements were always performed on the same sample, and care was paid to check that the recycling did not cause any saturation effect on the crystal. For any T01, the corresponding glow-curve is characterized by a single peak at temperature TM~which shifts towards higher temperatures as T~increases. The most obvious explanation of this trend is to admit a continuous distribution of traps. Though we are at present considering the methods of Bube Ct at,” we got an approximate evaluation of the features of the trap distribution through a refinement of an idea of Garlick and Gibson.25 The area enclosed under the curve obtainedwith excitation at To 1 is proportional to the total number of carriers released from the traps during the heating process, when allowance is made for the temperature dependence of the luminescence efficiency. The difference between the areas related to and is therefore proportional to the total number of carriers released from
Vol. 13, No. 11
OPTICAL PROPERTIES OF ZnIn2S4
I
I
I
To1. We can therefore build the curve of the distribution of the filled traps as a function of T01 the relation between To1 and E0, may then be obtained, approximately, with the method of the initial rise;~assuming in the limited range of temperature under investi-
1
20
2
1
-
78 ‘1<
2
-
89 ‘1<
gation, that this relation is linear, got which E~= 2.54 should give we results are T0. This method, which26will be p~esented and discussed in detail elsewhere, approximately independent on the kinetics of the
5 148 01< 67 - 169 190 ‘1< 01<
10
0
processes involved; when applied to the data of Fig. 2, it leads to the curve of Fig. 3, which gives the distribution of the traps, as a function of the energy below the ‘intrinsic’ absorption. This distribution is well approximated by an exponential curve, whose ‘slope’ is 160 ±20 meV/decade. This value has been checked also by analyzing the phosphorescence decay; in the case of an exponential distribution of trape, it is easily shown that Ip~follows, at long times, a power law, from which the value of the exponentail ‘slope’ can be found.27 (This procedure
-
“k
6
150
200
TEMPERATURE (~K)
FIG. 2. Thermoluminescence emission for different values of the excitation temperature. I
100
•\. \
disorder effect causes a broadening of the energy levels. In particular, the exponential distribution of Fig. 3 is consistent with the presence of fluctuations in the crystal potential, caused by structural defects, like vacancies, which give rise not simply to an exponential tail in the absorption, but to real localized states which act as traps for the carriers.
\
\
10
\
2 200
300
can be shown to be independent on the kinetics involved). The results of this analysis (150 ±30 rneV/ decade) are also in agreement with the TL value. A continuous distribution of traps is easily explained in a defective semiconductor, since any
I
\
z
1807
\
\ •\
400 ENERGY (m.V}
500
FiG. 3. Traps distribution vs energy below the intrinsic absorption. the traps enclosed in an energy region ~ where is an energy associated with the temperature —
Both optical and TL measurements, in conclusion, confirm the picture of ZnIn 2 S4 as a quasi-disordered crystal, in which the disorder effects prevail in the region of the absorption edge and below, where the effects of the ‘intrinsic’ structure are weaker or absent. This picture is also consistent, in view of the layer nature of 28 thiswho compound, with theory of has shown thata recent the formation Gubanov, energy for a fluctuation in the crystal potential decreases with the ‘dimensionality’ of the crystal itself. M~interesting point is represented by the closeness
between the values of the slopes of the absorption tail and that of the trap distribution, analoguously to what has been found in As 29 Ifwe assume that 2 S3. the number of filled traps, at any energy, is proportional to the localized states concentration, this
1808
OPTICAL PROPERTIES OF ZnIn2 S4
closeness thatabsorption the localized levelstransitions play directly a relevantsuggests role in the process; between extended and localized states, as responsible for the exponential tail, have often been invoked, but also questioned, in the hterature on the amorphous semiconductor.30 Anyway, the relation itself between the real density of states and the absorption edge tail
Vol. 13, No. 11
21’81 that any definite is so controversial andvery obscure, conclusion would be premature at present. Acknowledgements We thank Dr. Paorici, who grew the samples used m this experiment and Prof. Fieschi for useful discussions. Thanks are also due to Dr. Guzzi for comments on the phosphorescence measurements. —
REFERENCES 1.
MO1’T N.F. and DAVIS E.A. Electronic Processes in Non-Crystalline Solids, Oxford University Press, Oxford (1971).
2.
ADLER D. Amorphous Semiconductors. Butterworths, London (1972).
3.
STUKE J. J. Non-Crystalline Solids 4, 1(1970).
4. 5.
FRITSCHE H. J. Non-Crystalline Solids 6,49(1971). GREENWOOD N~N.Ionic Crystals, Lattice Defects and Nonstoichiometry, Butterworth, London (1968).
6.
RADAUTSAN S.J. Non-Crystalline Solids 4, 370 (1970).
7.
LAPPE F., NIGGLI A., NITSCHE R. and WHITE J.G. Kristall. 117, 146 (1962).
8.
GREENAWAY D.L. and HARBEKE G. Optical Properties and Band Structure ofSemiconductors. Pergamon Press, Oxford (1968). BALDINI G., BOSACCHI A. and FRANCHI S. Rapporto MASPEC No.2 (Dec. 1971).
9. 10.
SHIONOYA S. and EBINA A.J. Phys. Soc. Japan 19, 1150(1964).
11.
HOPFIELD JJ. Comm. Solid State Phys. 1, 16 (1968).
12.
DOW J.D. and REDFIELD D. Phys. Rev. B5, 594 (1972).
13. 14.
BOSACCHI B. and ROBINSON J.E. Solid State Commun. 10, 797 (1972). REDFIELD D. and AFROMOWITZ M.A.Appl. Phys. Lett. 11, 138 (1967).
15. 16.
MANCA P., MUNTONI C., RAGA F. and SPIGA A. Phys. Stat. Sol. (b) 44, 51(1971). See, for example, TAUC J.Mat. Res. Bull. 5,721(1970).
17. 18.
LANYON H.P.D. Phys. Rev. 130, 134 (1963). TAUC J. In Optical Properties ofSolids (edited by Abeles F.) North-Holland (1968).
19. 20. 21.
DAVIS E.A. and MOTT N.F. Phil. Mag. 22, 903 (1970). BONCH-BRUEVICH V.L. and ISKRA V.D., Fiz. Tekh. Poluprov. 5, 1948 (1971) [Soy. Phys. Semicond. 5, 1690 (1972)]. BONCH-BRUEVICH V.L. Phys. Stat. Sol. 42,35 (1970).
22. 23. 24. 25.
ESSER B. Phys. Stat. Sol. (b) 55, 503 (1973). BOSACCHI A., BOSACCHI B., FRANCH1 S. and HERNANDEZ L. to be published. BUBE R.H., DUSSEL G.A., HO C.—T. and MILLER L.D. J. Appi. Phys. 37,21(1966). GARLICK G.FJ. and GIBSON A.F.Proc. Phys. Soc. 60,574(1948).
26. 27.
BOSACCHI A., BOSACCHI B. and FRANCHI S. to be published. RANDALLJ.T. and WILKINS M.H.F. Proc. R. Soc. A 184,390(1945).
28. 29.
GUBANOV A.I. Fiz. Tekh. Poluprov. 6, 1378 (1972) [Soy. Phys. Semicond. 6, 1202(1973)]. ANDRIESH A.M., SHUTOV S.D. and IOVU M.S. Phys. Stat. Sol. (a) 11, K43 (1972).
Vol. 13, No. 11
OPTICAL PROPERTIES OF ZnIn2S4
1809
30.
See, for example, TAUC J. and MENTH A. J. Non-Crystalline Solids 8—10, 569 (1972), and also references 4, 16, 18 and 19.
31.
DOW J.D. and HOPFIELD JJ. J. Non-Crystalline Solids 8—10, 664 (1972).
Nous avons mesuré l’absorption optique et La thermoluminescence des monocristaux de ZnIn2 S4. On a trouvé un c~téd’absorption et une distribution de pièges qul dependent exponentiellement de l’énergie de Ia radiation, avec La méme ‘pente’. Les resultats montrent quil existe une quantité considerable de désordre intrinséque dans cc compose, et nous permettent de relier la discussion au probleme plus vaste des proprietCs optiques des semiconducteurs amorphes.