NON-STOICHIOMETRY AND SOLID SOLUTION IN ADAMANTINE TERNARY COMPOUNDS

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NON-STOICHIOMETRY AND SOLID SOLUTION IN

ADAMANTINE TERNARY COMPOUNDS

B. Pamplin

To cite this version:

B. Pamplin. NON-STOICHIOMETRY AND SOLID SOLUTION IN ADAMANTINE

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JOURNAL DE PHYSIQUE Colloque C3, supplbment au no 9, Tome 36, Septemhre 1975, page C3-53

NON-STOICHIOMETRY AND SOLID SOLUTION

IN ADAMANTINE TERNARY COMPOUNDS

B. R. PAMPLIN

School of Physics, University of Bath, Bath BA2 7AY, England

Rksumk. - La consideration des phases possibles de structure adamantine, qui satisfont Zi la rkgle des 4 Clectrons par site, conduit a des diagrammes de solutions solides qui indiquent comment differents atomes d'impuretes peuvent Ctre incorporCs dans les composCs I-111-V12 et 11-IV-V2 sans effet de dopagc.

Abstract. - A consideration of the possible adamantine phases which satisfy the four electrons per site rule, leads to solid solution diagram which indicate how various impurity atoms may be incorporated into I-111-VIZ and 11-1V-V2 compounds without a doping effect.

Introduction. - A study of possible adamantine ternary phases [l] predicts the following allowed compounds see Table I.

Many adamantine ternary compounds notably the IT IV V, compounds [2] can be best grown by slow cooling of a metallic magma solution. Inevitably some of the metal solvent atoms will be incorporated in the grown crystal. If, as is common, a component metal is chosen as the solvent, this may be expected by law of mass action considerations to enter the lattice in excess of its stoichiometric proportion as for example Sn in ZnSnP, grown from molten tin. The purpose of this paper is to discuss from a theo- retical viewpoint the nature of the grown crystal under such conditions. Some conclusions will also apply to vapour or melt grown crystals. The dis- cussion will also be widened t o mention the possible

mechanisms for inclusion of impurity atoms during growth.

The magma or mother liquor from which the crystals are grown consists usually of a solvent metal M and stoichiometric weights of the proposed crystal compound together with trace impurities. It is thus rich in the three required elements and M which may also bc one of the required elements. Then as the first crystals grow there is no shortage of any of these elements.

Consider a I1 IV V, compound ABX, growing from a group 111 metal M such as In. M can form an adamantine phase MX which is a 111 V compound. Thus the resultant purely adamantine phase to be expected is a solid solution or alloy of M X and ABX,. This is often observed in practice.

Similarly growing from a group IV metal such as

PNICTIDES

n

IV, V, no examples known I IV, V, CuSi,P, CuGe,P3

I1 1V V, BeSiN, MgSiN, MgSiP, MgGeN, MgGeP, CaSiN, CaGeN, MnSiN, MnGeN, ZnSiP, ZnSiAs, ZnGeN, ZnGeP, ZnGeAs, ZnSnP, ZnSnAs, ZnSnSb, CdSiP,

CdSiAs, CdGeP, CdGeAs, CdSnP, CdSnAs, CHALCOGENIDES

q I V AI, OS3 Al,0Se3 Ga, OS, Ga,OSe, Ga2OTe3 In,0Se3 I n 2 0 T e 3 I 111 VIZ CuAlS, CuAlSe, CuAiTe, CuGaS, CuGaSe, CuGeTe, CuJnS,

CuInSe, CuInTe, CuTIS, CuTlSe, CuFeS, CuFeSe, AgAlS, AgAlSe, AgAlTe, AgGaS, AgGaSe, AgGaTe, AgInS, AgTnSe, AgInTe, AgFeS, (and CuSbS,, CuBiS,)

IV VIZ no examples known

I, IV VI, Cu,SiS3 Cu,SiTe3 Cu,GeS, Cu,GeSe, Cu,GeTe3 Cu,SnS, Cu2SnSe3 Cu2SnTe3

u3

V, VI, no examples known

I, V VI, Cu3PS4 Cu3AsS4 Cu3AsSe4 Cu3SbS, Cu3SbSe4

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C3-54 B. R. PAMPLIN

Sn may be expected to produce an alloy of the hypo- thetical adamantine phase O M 3 X 4 and the desired compound ABX,. This can be assigned the compo- sition

A1 -2xB1-2xM3xOxX2 or if M is identical with B

A1-2xB,+xOxX4.

Such a formula satisfies the four electron per site rule [3] and shows how extra groups four atoms can be

accommodated in the crystal lattice with associated vacancies to produce an intrinsic alloy.

It may be argued that such material is best regarded as compensated rather than intrinsic with metal vacancies which on Krogcr's hypothesis will be acceptors and an equal number of B on A sites which will be donors. Such donors and acceptors would be expected to associate in the lattice if growth conditions permit to form complexes which may introduce levels in the gap. (Notice also that balanced antistructure disorder - i. e. B on A and A on B disorder,

-

would

Table of substitution und solid solution possibilities

A. Metal M substituting in I1 IV V, compounds ABX,. Group for M Substitution possibilities

-

I No substitution possible without acceptors I1 M substitutes for A

(M cannot substitute for B except as an acceptor) I11 M substitutes for A with cation vacancies

M,X, forms solid solution

(M substituting equally for A and B) M substitutes for A and B

(M cannot substitute for B alone except as an acceptor) 1V M substitutes for A with cation vacancies

M substitutes for B

M, O X 4 forms solid solution (substituting for A and B equally) M substitutes for A and B V M substitutes for X

on anion lattice

(There are possibilities for M or A and B sites but this is chemically unlikely)

V1 Substitution without doping is unlikely

B. Metal M substituting in I I11 VI, compound ABX, I M substitutes for A

(M cannot substitute for B except as an acceptor) I1 M substitutes for A with cation vacancies

M,X, forms solid solution

(M substituting equally for A and B) M substitutes for A and B

(M cannot substitute for B alone except as an acceptor)

111 M substitutes for A with cation vacancies M substitutes for B

M , O X 3 forms solid solution (substituting for A and B equally)

M substitutes for A and B with cation vacancies IV M substitutes for A with cation vacancies

M substitutes for B with cation vacancies

M O X , forms solid solution (substituting for A and B equally)

M substitutes for A and B with cation vacancies

V M cannot substitute for X without being an acceptor. It is chemically unlikely to substitute for A or B

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NON-STOICHIOMETRY A N D SOLID SOLUTION IN ADAMANTINE TERNARY COMPOUNDS C3-55 also produce donor acceptor pairs of similar pro-

perties.)

Solid solutions of thc 111,~V13 compounds with I11 V compounds have shown that at low concentra- tions of the ternary in the binary vacancy formation on the metallic lattice does not occur. For example [3] Te in lnAs is a good donor, - the expected adamantine solid solution does not occur until about 1 0/,

ln,Te, is added to InAs. The same effect occurs, but is less marked when alloys of Il12UV13 and I1 V1 compounds are considered.

Thus we d o not except all the vacancies in formula (I) to occur at low concentrations and M will act as a donor in the ternary compound. Most tin grown crystals such as ZnSiP, are found to be n-type. How- ever ZnSiAs, is p-type and this must be explained as due to arsenic vacancies ; for it is always p-type however the crystals are grown.

Consider now in contrast the situation when ABXl is grown from a group 11 (or group 1) metal M.

There are no possible adamantine phases for these groups alone with group V, thus no excess M can enter the lattice without a doping eflect. We have grown ZnSiP, from Zn solution and obtained high resistivity p-type crystals. This is consistent with the prediction that any excess zinc in the lattice can only replace silicon (or phosphorus) and act as an acceptor. The only other possibility is that it enters interstitially.

I t is perhaps worth noting that if group I and group IV are present together as solvent and/or impurities an adamantine solid solution of the form (11, IV, V,), -,(I, lV4 V,), is possible.

I I11 V1, compounds are commonly prepared by vapour transport although Yamamoto and Miyau- chi [5] have used metal solutions.

Consider inclusion of a group 11 metal. This can clearly give an adamantine solid solution of the form (ABX,), -,(M,X,), in which there are no vacancies.

If M is a group I11 metal a solid solution of the form A, - ,,B3 - 3,M2,~4,X6 is clearly possible and

this case is entirely parallel to that of group IV in 11 IV

v,.

Groups IV and V can be accommodated using the adamantine compounds I, IV V, and I, V V1, as alloying partners.

However group I cannot be accommodated in excess by any adamantine solid solution and if it enters the lattice it must form an acceptor site unless it enters interstitially.

Table I1 gives an exhaustive list of the substitution and solid solution possibilities for an impurity metal M entering the chalcopyrite lattice of an ABX, compound. Since there are usually two sites on which the foreign atom M may be expected to substitute the general solution of the substitution problem leads t o a range of possible adamantine phases. This

Group JII in lIIPPz FIG. 1

Group

IP

in IIEP,

FIG. 2.

Group I1 in IIlIl7I2

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B. R. PAMPLIN

Group III in

I

IlI

XLz

FIG. 4.

range, with the inclusion of vacancies, is not a simple line in the phase diagram but in some cases (e. g. 111 and IV in I1 IV V, and 11, I11 and IV in I 111 VIZ) leads to an area of the phase diagram being a possible adamantine phase of variable composition. It is unlikely that all compositions in such an area can be prepared, but rather that some line will bc the preferred composition line within the possible area. The figures show the ranges of possible adamantine solid solution. The actual situation will be complicated by devia- tions of stoichiometry from the ideal phases and this

Group 1P in

I

IE

PT2

FIG. 5.

will lead to n- and p-type material as can be predicted. For example, the filling in of expected vacant lattice sites yields n-type material as has been illustrated above, whereas the formation of excess vacancies would be expected to produce p-type material.

Knowledge of the possible adamantine phases will enable growers of crystals who know which impurity is dominant in their growing medium to predict the effects on stoichiometry and with the added infor- mation about conductivity type to propose a crys- tallochemical model for impure and doped crystals.

References

[ l ] PAMPLIN, B. R., J. Phys. Chem. Soli(1.~ 25 (1964) 675. [4] WOOLLEY, J. C., PAMPLIN, B. R . and EVANS, J. A., J. Phys. [2] PAMPLIN, R. R., J. Cryst. Growth 26 (1974) 239. Chenz. Solids 19 (1961) 147.

[3] PAMPLIN, B. R., Nutlire (London) 188 (1960) 136. [S] MIYAUCHI, T. and YAMAMOTO, N., J. Physique Colloq. 36