DEFORMATION LUMINESCENCE IN II-VI CRYSTALS

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DEFORMATION LUMINESCENCE IN II-VI CRYSTALS

S. Bredikhin, S. Shmurak

To cite this version:

S. Bredikhin, S. Shmurak. DEFORMATION LUMINESCENCE IN II-VI CRYSTALS. Journal de Physique Colloques, 1983, 44 (C4), pp.C4-183-C4-188. �10.1051/jphyscol:1983422�. �jpa-00223041�

JOURNAL DE PHYSIQUE

Colloque C4, supplément au n°9, Tome 44, septembre 1983 pageC4-183

DEFORMATION LUMINESCENCE IN I I - V I CRYSTALS

S . I . B r e d i k h i n and S.Z. Shmurak

Institute of Solid State Physios, U..S.S.R. Academy of Sciences, Chernogolovka, U.S.S.R.

Résumé - On a étudié les mécanismes d'interaction entre les dislocations en mouvement et les types différents de centres optiquement et électriquement actifs dans des monocristaux des composés II - V I .

Abstract - This work treats the mechanism of interaction bet- ween moving dislocations and different types of optical and electrical centers in II-VI compounds,

The phenomena of deformation luminescence (DL), i.e. luminescence due to plastic deformation of crystals was investigated careffully.

A parallel investigation of deformation emission, photoluminescence and electric characteristics of the deformed sample has made it pos- sible to establish that the DL is the result of excitation of lumi- nescence centers by moving charged dislocations. The proposed DL mechanism consist in that the electrons tunnel from the luminescence

centers into the conduction band in the strong electric field of mo- ving charged dislocations, with a subsequent radiative recombination of this electrons on the ionized luminescence centers.

1 - CHARACTERISTICS OP DISLOCATIONS

To determine the mechanism of deformation luminescence we have stu- died in detail different types of dislocations moving due to plastic deformation of ZnS and ZnSe crystals. It has been previously estab- lished /1-3/that the plastic deformation down to 17% in ZnS single crystals is the result of motion of partial dislocations. This is the only known case when partial dislocations affect essentially the properties of crystal.

How it is well known that dislocations in ZnS and ZnSe crystals are charged. A detailed investigation of the linear charge density of dislocations and of its dependence on the sample temperature and strain rate are reported in Ref. /4-7/»

The dislocation charge was measured by the method of dislocation cur- rent, i.e. we measured the charge brought to the sample surface by moving dislocations Q= /Iddt (where 14 is the current due to moving dislocations) Pig. 1.

Our experiments showed the proportionality of Iq to the strain rate

£. , the existence of the dislocation current only at 6^6"«£» and the absence of Id after the deformation is stopped.

To estimate an average value of the dislocation charge we assume that during deformation only one type of partial dislocations moves in ZnS crystals /5/> and then we obtain to

c\=^(Mfudt4h ⁽²⁾

o

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983422

JOURNAL DE PHYSIQUE

4 6 8

t,

min

Pig. 1

-

Diagram of deformation (curve 1 ). In tensity of deformation luminescence (curve 2). Dislocation current (curve 3).

The presence of charge on dislocations should result in electrostatic interaction between the applied external electric field and moving ch=ged dislocations. In fact, we observe a change in plasticity of crystals while turning-on the external electric field during deforma- tion (Pig. 2). An increase or decrease in plasticity of crystals is due to the polarity of the external electric field (the so called

"odd" electroplastic effect). If we know the change of the mechanical stress magnitude a 6 due to the external electric field U

,

^{then the}

value cex also be determined q=b,6/2u

The values of the dislocation charges obtained by the methods of dis- location current and by another method of llodd* electroplastic effect are in good agreement.

OFF

I

Fig. 2

-

ZnS crystal deformation diagram. Arrows indic te mome ts turn-on and turn-of of the electric field (E=IOkV/cm)

;%

^{~ 3 .} 10-ycels-'.

The dislocation linear charge density

( 9

) is shown to depend on many factors namely, strain rate, temperature, and impurity content

(Table 1 ).

Dislocation charge in ZnS at 300K and

&

^=3. I O - ~ S ~ G - ~

-

Sample SnS SnS-Ni ZnS-Mn ZnS-Cu-Al

Concentration of Ni, En, Cu, A l

lom2$

Pig. 3

-

Temperature dependence of the dislocation linear charge density in ZnS-Cu, Al crystals,

Fig. 3 shows the dependence of dislocation linearlcharge density on the sample temperature at a constant strain rate /-J =lO,wm/min, Incre- ase in temperature leads to decrease in

9

^; at T=300°K 9=0,34e/site and at T=390K 9=0,2Ie/site.

In investigated ZnS crystals the Debye screening radius (Ra) was of the order of Imm. Therefore, the free carriers cannot screen the ra- dial electric field E around the aislocations, which has the geometry similar to that of the electric field of a charged filament -

(31 where 5 * 7 is the dielectric constant of the ZnS crystal and

r

^is

the dis ance to the dislocation core. At a li ear dislocation charge density

7

=0,34e/site and a distance

r

^=l~-gcrn from the dislqcatlon core the electric field intensity

E

was found to b e € =3,4.10-v/cm.

A stationary electric field of the same intensity, applied to ZnS sa- mple, causes electrons to tunnel from the centers to the conduction band

/a/.

Consequently tunneling of electrons from impurity levels and capture centers into the conduction band can occur in ZnS crys- tals in electric fields that exist around the moving charged disloca- tions (f)). The free electrons produced thereby can get radiatively recombined on the produced hole centers C+ and cause the sample lumi- nesce. 'Phis process can be represented schematically

D + C -

C4-186 JOURNAL DE PHYSIQUE

2

-

I ~ C H ~ L ~ ~ I S H OF D E F O ~ T Z O N LW~NESCENCE. SPECTRAL BND TEMPERA'PURE CHARACTERISTICS

As noted above ZnS crystals luminescence all the time in the course of plastice deformation /9/. Pig. 1 shotvs a plot of the deformation and of DL inZnS-Gu, A l single crystals at a constant deformation rate of =I0 m/&n. It is seen that deformation luminescence does not occur in t

C

e elastic region and appears only at plastic deforma- tion. An increase of the deformation rate causes a proportional growth of the emission intensity.

The appearance of deformation luminescence in 11-VI crystals can be explained by taking into account the presence of the electric fields around the moving dislocations. As far back as in 1958, Keldysh had shown /8/ that electron-hole pairs are produced in seniconductors i n

a strong electric field by tunneling electrons from the valence to

%he conduction band, A theory of electron tunneling from deep impuri- ty levels into the conduction band in strong electric fields with regard to the multiphonon processes has been subsequently deveiopted.

Consider now the mechanism of excitation of centers when charged di- slocations move in a crystal. The electric potential surrounding the dislocations bends the valence and conduction bands. The electron center "floats uptt in synchronism with the band bending as the dislo- cation core approahes them. Starting with a certain distance from the dislocation core, the processes of electron tunneling from the cen- ters into the conduction band become significant (Pig. 4).

V - band

Fig. 4

-

^The scheme of the processe of electron tunneling from the oenter into the conduction band.

Parallel investigations of spectral and temperature characteristics of photoluminescence and deformation luminescence shows that DL in XI-VI: compounds is an intracenter glow of the available activators.

The interaction between ch~lrged dislocations and electrons located at the deep levels

(uo

=0,7eV from the bottom of the conduction band) was studied, Our m e a e e m e n t s showed that the experimental effective radius (Reff) of dislocation ' teraction with these deep levels pro- ved to be gqual to Reff=5.l0Ycm. A numerical estimation of

(R

=lo'

cm) carried out in the quasiclassZca1 approximation a

g

!

&

%

s wee1 with the exprimental value,

3

-

^{THE SUWACE} PULSED Di3BORaUTION ELECIPROLUNINESCENCE OF ZnS C R m m In addition to the stationary deformation luminescence of 11-VI com- pounds, the emission of short pulses resulting rom the deformation of high resistance ZnS single crystals ( Q z l O 14 om cm) also occurs, i,e, the Zwninescence has a nonstationary character. The amplitude and duration of the luminescence pulse is independent of the deforma- tion rate or temperature, On the other hand, the number of lumines- cence pulses per unit time (N) is detemined.by.the plastic deforma- tion rate€

,

and is always proportional t o E E=&.JJ. The spectrum of the pulse luminescence consists of a series of narrow bands in the region of 290-430m (2976, 3158, 3365, 3535, 3576 A) Fig. 5 1

Big. 5

-

^Pulsed luminescence spectrum of ZnS-En crystal.

In the luminescence spectrmm of samples doped vdth manganese the h- purity luminescence from ions (Ama=585nm) is observed in addi- tion to the narrow bands, The luminescence spectrally coincident with a pulsed deformation luminescence was observed on exciting surface electroluminescence of ZnS single crystals. IChe short-wave bands

(290-43011~) were ascribed to the luminescence of the atomic oyygen absorbed by the surface, !?he coincidence of the spectra of both pro- cesses indicates that the mechanism of these phenomena are similar, In fact, the moving charged dislocations bring to the crystal surfa- ces a charge which is accumulated on the surfay3 due to low concen- tration of free carriers in the sample ( Q = 10 om cm).IPhe.differenoe i n potential between the sample surfaces is responsible for the appe- arance of the electroluminescence pulse after reaching the breakciown voltagevb,

.

^{A potential}

^v

equal to the breakdown value v b , can be generated between the surfaces of the sample provided that the dislo- cation current id producing this potential exceeds the leakage cur- rent through the crystal, i.e. :

- -

^,

Id>

vbp/~

Brpm eq (2) me obtain sample

Hence, lunineecence pulses can occur only if the following inequality is fulfilled

C4-188 JOURNAL DE PHYSIQUE

Por the investigated crystals this condition is fulfilled at deforma- tion rate h> 3 m/min. At h<3pm/min no luminescence pulses should be observed. T&s assumption is perfectly supported by the experime- ntal results.

In this work we investigated different mechanism of the deformation luminescence due to the movement of charged dislocations in 1 1 - V I cor;lpoun&s It is shown that:

1. In strong electric fields produced by charged dislocations, the electrons from impurity levels and capture centers tunnel into the conduction band ( the first stage of DL). The recombination of the electrons released by dislocations with the ionized luminescence centers leads to intracenter luminescence (the second stage of DL).

2. Tho charge brought to the crystal surface by moving chazged

dislocations is responsible for the surface pulse electroltnninscence.

REFERENCES

/I/ Ossipyan Yu.A., Smirnova I.S. J. Phys. Chem. Sol.,

a,

¹⁵²¹

(1971).

/2/ Abdikamalov B.A., Bredikhin S.I., Kulakov N.P., Shekhtman V.Sh and Shmurak S.Z. Fiz. Iverd. Pela (Leningrad)

18,

2468 (1976) ;

Sov. Phys. Sol. State 18, 1442 (1976).

/3/ Kulakov N.P., Shmurak

ZZ.

Phys. Stat. Sol. (a)

2,

147 /4/ Bredikhin S.I., Sbmurak S.Z. Pistma Zh. Eksp. Teor. FLZ.

21,

342 (1975); JETP Lett.,

21,

156 (1975).

/ 5 / Bredikhin S.I., Shmurak S.Z. Zh. Eksp. Teor. Fie.,

12,

1460 (1977); Sov. Phys. JETP

$,

768 (1977).

/6/ Ossip an Yu.A., Petrenlso V.P. Zh. Eks

.

Teor. Piz.,

a,

¹³⁶²

(19757; SOV. P~YS. JETP 41, 695 (19758.

/7/ Kirichenko L.G., Petrenko V.F., Uimin G.V. Zh. Eksp. Teor. Fiz.

742 (1978) ; SOV. Phys* JETP

41,

389 (1978).

/8/ &%dysh L.V. Zh. Eksp. Teor. Fiz.,

,

994 (1957) ;

,

⁹⁶²

(1958) ; Sov. Phys. JETP

6,

763 (195%;

2,

665 (1958%

/9/ Bredikhin S.I., Shmurak S.Z. Zh. Eksp. Teor. Fiz.,

76,

1028 (1979); Sov. Phys. JETP 49, 520 (1979).