Materials Chemistry and Physics 90 (2005) 148–154 Soft g alk n∗, N General Ch nivers mber 20 Abstract The electr f a zin and a mecha s (bath deposition ti was in by means of rge am variants of t ichiom is possible. © 2004 Else Keywords: Z 1. Introdu Zinc selenide is a semiconductive material capable of a number of optoelectronic applications, such as blue-light photo-electronic diodes and lasers as well as photovoltaics where it can be advantageously used as buffer, or window layer in ch ber of tech tion, molec por deposit ZnSe. Also have becom [1–3] for v sition from the prepara characteriz chiometry in these pro of an elem synthesis o We repo using the s ∗ Correspo E-mail a e envi been successfully used for the production of thin films of cadmium selenide and zinc sulfide by electroless-chemical [4,5] and electrochemical [6–11] methods, while the prepa- ration of Zn chalcogenides [12–15] is more difficult to at- tain due to complications in electrochemistry. Taking into 0254-0584/$ doi:10.1016/j alcogenide-based thin-film solar cells. A num- niques, like sputtering, electron beam evapora- ular beam epitaxy and metallorganic chemical va- ion have been employed to prepare thin films of , soft growth techniques, such as electrodeposition e very attractive. There have been several reports arious alternatives of ZnSe cathodic electrodepo- aqueous solutions of selenious acid leading to tion of polycrystalline films, which, however, are ed by poor integrity due to the absence of stoi- and microcrystallinity as well. The major problem cesses is to encounter the unrestrained formation ental Se phase in the deposited layer during the f the binary compound. rt here that the excess of Se might be avoided elenosulfite ion as a selenium precursor in an al- nding author. Tel.: +30 210 7723097; fax: +30 210 7723088. ddress:
[email protected] (M. Bouroushian). account these approaches, we bring forward here the out- come of a long series of experiments with selenosulfite al- kaline solutions intended to achieve the formation of stoi- chiometric ZnSe. The effect of various process parameters, namely the electrical variables, bath composition, tempera- ture and state of the substrate are investigated in terms of the structural and morphological properties of the deposited layers. 2. Experimental details A three-electrode cell fitted to a potentio-scan system (Wenking PGS 81R) with an either rotating (500 rpm) or non- rotating cathode set-up was used in order to perform electro- chemical experiments. The counter electrode was a platinum grid and the potentials referred to a commercial Hg/Hg2SO4 saturated sulfate cell (SSE). Cathodic electrodeposition – see front matter © 2004 Elsevier B.V. All rights reserved. .matchemphys.2004.10.027 rowth of the ZnSe compound from T. Kosanovic, M. Bouroushia emistry Laboratory, School of Chemical Engineering, National Technical U Received 3 June 2004; received in revised form 24 Septe odeposition of ZnSe from alkaline selenosulfite, (SeSO3)2−, baths o nistic interpretation manner. The effect of various process parameter me) on the structural and morphological properties of the deposits X-ray diffraction and scanning electron microscopy (SEM). A la he presently described method showed that the production of a sto vier B.V. All rights reserved. nSe; Thin films; Crystal growth; Selenosulfite solution; Powder diffraction ction kalin aline selenosulfite solutions . Spyrellis ity of Athens, Zografos Campus, GR 15773 Athens, Greece 04; accepted 5 October 2004 c ion complex has been studied both in an experimental composition, substrate nature and rotation, temperature, vestigated. The structure-related results were valuated ount of experimental data issued by applying multiple etric, though amorphous in structure, ZnSe compound ronment. The selenosulfite-based solutions have T. Kosanovic et al. / Materials Chemistry and Physics 90 (2005) 148–154 149 under galvanostatic, potentiostatic as well as pulse-plating conditions was applied in order to obtain the thin films. Several for the cath Ti and Ni d alumina po before dep HF for 10 s ther, severa a potentios cathode vo 60 min, in a trodes were 15–30 min. CdSe-elect described i glass electr suitable ca 30 s in a so and temper to form a v nucleation The elec aqueous, n containing [(SeSO3)2− or ethylene peratures o were made mixed. A s solution of 0.5 M in N [4]. The zi ZnSO4 into (NTA or E plex, the so trolysis can bath was c lution. All 18.3 M� cm received an The str mined by ray diffract positional dispersive apparatus. 3. Mechan 3.1. Seleno The sele solving ele sulfite: Se + (SO3)2−↔ (Se0SO3)2−. (1) s the e h con ed to o action : (HSO ighly d by th O3)2− e SeS t oxid to oc es, su d sele Se tha e. O3)− Metal n adeq ine sol of a c and n der to xide ng age ree zin s their t (NH3 ion is: )n2+ SO42− lfate t of th ide, bu directl lenosu te salt itive e e [5]. oreov on pot ls, com a com s used types of electrodes and pretreatments were used odic substrate of deposition. Commercially pure isks (≈1.13 cm2), abraded and polished by 0.3�m wder were subjected to the following treatments osition. The Ti electrodes were etched by 10% in order to dissolve the surface oxide layer. Fur- l Ti specimens were anodized after etching in tatic manner, namely with a constant anode-to- ltage drop of 20 or 50 V applied during 1, 15 or n electrolyte of 1 M sulfuric acid. A few Ni elec- roughened in diluted nitric acid (1:3 or 1:10) for Also, SnO2-covered glass electrodes as well as rodeposited films on Ni (according to a method n [16]) were used as substrates. The conductive odes were activated before each experiment by a thodic treatment, i.e., polarization at −1.2 V for lution of similar working bath ionic strength, pH ature in order to clean up the SnO2 surface and ery thin layer of metallic tin, which promotes the of the electrodeposit. trodeposition process took place in air-saturated, ear-neutral to alkaline solutions (pH 7–13) various concentrations of selenosulfite anion ], and Zn complexed with nitrilotriacetate (NTA) diamine tetraacetate (EDTA) anion, at bath tem- f 25–85 ◦C. The SeSO32− and Zn complex species in situ in separate solutions, which were then elenosulfite stock solution was prepared by dis- elementary black Se (0.2 M) in a fresh solution a2SO3 under an inert argon atmosphere at 70 ◦C nc complex solution was prepared by dissolving an aqueous medium of a strong complexing agent DTA) of limiting excess. By means of this com- lution remains stable for at least 48 h so that elec- be repeated several times. The pH value of the ontrolled by addition of a sodium hydroxide so- the above solutions were prepared by water (of ), purified by an ultra-pure water system and as- alytical grade reagents. ucture of the as-prepared deposits was deter- diffractometry in a Siemens D5000 powder X- ion (XRD) unit with a Cu K� source. The com- data of the deposits were obtained by energy- X-ray (EDX) spectroscopy in a JEOL JSM 6100 istic approaches sulfite solutions nosulfite anions (Se0SO3)2− are prepared by dis- mental selenium in an alkaline solution of sodium A a hig need ing re right Se + and h erate (Se0S Th do no likely speci erate free sulfit (HSe 3.2. A alkal tion NH3 in or hydro plexi the f mine agen react Zn(A + Su resul selen ther of se sulfa a pos lenid M ducti meta fore, tem i quilibrium constant of this reaction is around unity, centration of sulfite and alkaline environment is btain the selenosulfite species. Then the follow- , involving hydrolyzed sulfite, is displaced to the 3)−↔ (SeSO3)2− +H+ (2) reactive selenide ions (Se2−) can be electrogen- e reaction [6]: + 2e−→ Se2− + (SO3)2−. (3) O32− and SO32− ions (or their protonated forms) ize Se2−. Electroforming of elemental Se is un- cur from this solution as high valency selenium ch as Se(+IV) that could oxidize the electrogen- nide ions (e.g. Eq. (4)) are absent. Moreover, any t may be formed would re-dissolve in the excess +Se2− + 5H+→ 2Se(s)+ 3H2O. (4) complex uately stable complex of the metallic ions in the ution of selenosulfite, resulting after the introduc- omplexing agent (EDTA or NTA), stronger than ot interfering with selenosulfite reduction, is used prevent the formation of the sulfite, sulfate and precipitates of the metal. The excess of the com- nts, including NH3, controls the concentration of c ions in the alkaline environment, i.e., it deter- applicable solubility. With A as the complexing , NTA, EDTA), the overall competitive chemical + (SeSO3)2− + 2OH−→ ZnSe+ nA +H2O. (5) ions may accumulate in the system not only as a e conversion of the complex metal salt into the t also from the oxidation of sulfite by oxygen ei- y in the reaction mixture or during the synthesis lfite. For analytical reasons, an amount of sodium is added to the reaction mixture. This may have ffect on the crystallinity of the formed metal se- er, the complexing agents shift negatively the re- ential of Zn, as has been observed also for various plexing agents and cathodic substrates [7]. There- plex metal salt–selenosulfite–alkaline reagent sys- . 150 T. Kosanovic et al. / Materials Chemistry and Physics 90 (2005) 148–154 3.3. Deposition mechanisms According to various reports [5–9,15], the synthesis of ZnSe a nism of Z involve: (i) reduc of the geneo (prove proce (Se0S [Zn(A Zn2+ (ii) reduc reacti Zn to prepa [Zn(A Zn2+ Zn(s) (iii) reduc ZnSe [Zn(A Zn2+ Zn(Se + ( The pote is already r operative f 3.4. Growt ZnSe is substrate o one impedi chemically may depos hesion (e.g reactions at of a segreg effective su a heterogen ZnSe occur ions as pre adsorption by an approximation of Se2− ion, and a relaxation of the Zn- complex bond. It is essential that a selenosulfite reduction occurs at the same time as Zn2+ reduction while the process ited b lation dsorp e rate t hom elenid at hig erefo ion as induc ns con tigatio omple ics as tially esults hen th dic to desc Accor edox p ver, th ulfite, cted to ibrium ss (ii) d at a aves action The ch dic sh eposit ol. e elec ations eratur olution in Ta nder >−1 conce (elect uction rding t recurs increa ◦C p n be o arious nd CdSe as well the electrochemical mecha- nSe formation in selenosulfite solutions may tion of selenosulfite to selenide ion in the vicinity cathode, followed by a homogeneous or hetero- us reaction of the latter with Zn2+ to form ZnSe d to be operative for CdSe preparation by a similar ss with A = EDTA): O3)2− + 2e−→ Se2− +SO32− (6) )n]x↔ nAy+Zn2+ (7) +Se2−→ ZnSe(s); (8) tion of Zn2+ free ions to Zn, followed by a chemical on of adsorbed selenosulfite with electrodeposited form ZnSe (proved to be rather operative for CdSe ration): )n]x↔ nAy+Zn2+ (9) + 2e−→ Zn(s) (10) + [(SeSO3)2−]ads↔ ZnSe(s) + SO32−; (11) tion of a Zn–selenosulfite complex directly to (see also [7]): )n]x↔ nAy+Zn2+ (12) + x(SeSO3)2−↔ Zn(SeSO3)x2−2x(aq) (13) SO3)x2−2x(aq) + 2e−→ ZnSe(s) x−1)(SeSO3)2− +SO32−. (14) ntial required for the dissociation of selenosulfite educing for the zinc ions, so this mechanism is not or the preparation of ZnSe. h aspects generated by a heterogeneous process on the r a homogeneous process in the liquid solution, ng the other. ZnSe produced homogeneously, i.e., in the liquid, precipitates in the cell bottom or it on the substrate on account of increased ad- . on rough surfaces or surfaces inducing chemical the interface). This process leads to the formation ation layer of amorphous ZnSe in our system. An rface deposition process is possible only through eous mechanism. In this case, the condensation of s having the selenide and adsorbed zinc complex cursors. The total process involves diffusion and of the Zn-complex ion to the substrate, followed is lim popu The a ing th a fas and s cially zinc. Th solut state ditio inves Zn c kinet essen 4. R W catho ously cell. the r howe lenos expe equil proce poun tion w inter fite. catho tial d contr Th centr temp ing s given U (Edep high ions prod acco the p The to 85 as ca for v y the adsorbability of the complex ion and the of the active sites for adsorption on the substrate. tion and relaxation comprise limiting steps lower- of the heterogeneous process. At the same time, ogeneous reaction occurs between the free zinc e ions provided in the bulk of the solution, espe- hly cathodic potentials and high concentrations of re, the availability of Zn2+ in a stable selenosulfite well as the electrical parameters, and the substrate ing adhesion and nucleation–crystallization con- stitute the critical factors for the process under n. In other words, the instability constant of the x in the working pH of the bath and the growth determined by the charged substrate surface are important. and discussion e potential of the working electrode is sufficiently reduce both selenosulfite and zinc, all the previ- ribed reactions [Eqs. (6)–(14)] may occur in the ding to voltammetry, the complexing agent shifts otential of zinc towards the cathodic direction; is stays positive to the reduction potential of se- so that the aforementioned mechanisms are not be operative at potentials more anodic than the value of selenosulfite. A possible exception is the , which could lead to the formation of the com- pplication potentials located between the reduc- of zinc and selenosulfite as involving a chemical between reduced zinc and adsorbed selenosul- oice of a proper complex resulting in a further ift would allow conditions of zinc underpoten- ion, which offers the possibility of better growth trodepositions were performed with various con- of precursors in the bath, different substrates and es. The final compositions of the employed work- s as well as the ranges of applied temperature are ble 1. A brief description of the results follows. a strong, constant cathodic polarization .8 V), the electrolysis in baths of relatively ntrations in both selenosulfite and zinc complex rolytes of type K and L, Table 1) leads to the of stoichiometric, amorphous ZnSe deposits, o XRD, as long as the cathode stays unrotated and ors’ concentrations are nearly similar (Fig. 1a). se of the bath temperature from room conditions romotes the formation of the ZnSe compound bserved for deposits formed at −2 and −2.1 V plating charges from solutions of type L and K T. Kosanovic et al. / Materials Chemistry and Physics 90 (2005) 148–154 151 Table 1 Composition and applied temperature range of employed electrodeposition baths Bath typea SeSO32− (mg mol−1) Na2SO3 (g mol−1) ZnSO4 (mg mol−1) NTA (mg mol−1) EDTA (mg mol−1) Ammonia buffer (g mol−1) pH T (◦C) A 1–10 0.1–0.2 10 10 – 1 7–11.5 55–85 B 1–10 0.02–0.1 200 200 – 0–1 9–12 25–85 C 1–10 0.1–0.2 10–200 – 200 – 9 55 D 8 0.2 8 14 – 1 9–10 55–85 E 25 0.05–0.1 25 45–60 – 0–0.5 9–11 25–85 F 25 0.1 25 50 – – 11–12 55–85 G 20 ≤0.08 20 25–28 – – 9–12 25–85 H 38–60 0.2 18–22 26 – – 9–10 35 I 40–50 0.1 40–50 – 40–50 – 10–12 25–85 J 80 0.12 80 140–180 – – 10–11 40 K 100 0.15 50–100 50–100 – – 9–13 25 L 50–100 0.15 50–100 – 100 – 9–13 25–85 a A–C solutions as referred also in [6]; E, F [7]; G [10]; H [8,9]; K, L [4]; J [11]. (Fig. 2). The dissociation of the complex depends on the temperature, so that heating is propitious to get a higher con- centration of zinc available for the reaction with selenosulfite anions. A higher than unity selenosulfite-to-zinc complex Fig. 1. XRD various worki on SnO2/glas 0.1 M EDTA produced dep of 0.025 M S 1.75 M NH3, (E1 =−1.6 V, SeSO32−, 0.1 pH 11, at 25 ◦ ratio of concentrations in the bath leads to the formation of Se-rich layers (Fig. 2b; ([Se]/[Zn] = 2). Similar results were obtained from baths of type E in the absence of ammonia buffer for all the working substrates by a galvanostatically controlled electrodeposition process (current I= 0.4 and 0.6 mA cm−2). Zinc-rich deposits were formed on the rotating cathodes from solutions of type J under all electrolysis conditions, whereas multiphase systems containing ZnSe, Zn and Se were depo potentials E was observ films produ count of the after a few slow oxida layer was t patterns of deposits prepared on non-rotating electrodes from ng baths with a similar electrolysis charge. (a) A layer obtained s at −1.8 V from a solution of 0.1 M SeSO32−, 0.1 M ZnSO4, and 0.15 M Na2SO3, pH 11.5, at 25 ◦C. (b) Galvanostatically osit (current I= 0.5 mA cm−2) on the Ti electrode for a solution eSO32−, 0.025 M ZnSO4, 0.05 M NTA, 0.1 M Na2SO3 and pH 12, at 55 ◦C. (c) Pulse-plated deposit on the Ti electrode E2 =−2.0 V, duty cycle 30% for 1 Hz) from a solution of 0.1 M M ZnSO4, 0.1 M NTA, 0.15 M Na2SO3 and 0.23 M NaOH, C; θ = diffraction angle. Fig. 2. XRD various platin trode at −2 a 0.1 M EDTA on the roughe SeSO32−, 0.0 sited on the non-rotating cathodes at deposition dep≥−2.1 V. No diffraction from elemental Se ed in the XRD patterns of the amorphous ZnSe ced from the solutions of type J. However, on ac- orange-red coloration acquired from the deposits hours, an amorphous Se phase resulting from the tion of occluded selenide precursors in the solid hought to be present. patterns of deposits prepared on non-rotating electrodes for g charges (3, 5 and 20 C). (a) Film deposited on the Ti elec- nd −2.1 V from a solution of 0.1 M SeSO32−, 0.1 M ZnSO4, and 0.15 M Na2SO3, pH 10.5, at 85 ◦C. (b) Film deposited ned Ni electrode at−1.4 and−1.5 V from a solution of 0.1 M 5 M ZnSO4, 0.05 M NTA and 0.15 M Na2SO3, pH 9.3, at 25 ◦C. 152 T. Kosanovic et al. / Materials Chemistry and Physics 90 (2005) 148–154 In the absence of elemental phases, the as-deposited layers exhibited a yellow color, typical for pure ZnSe, whereas an either gray or orange-red coloration was observed depending on whether they contain an excess of Zn (obtained at very negative potentials) or Se (at high selenosulfite concentra- tion), respectively. Commonly, electrolysis in baths of medium concentra- tions of the precursor species (types: D, F, and G) results in the production of unstable systems excessive in elemen- tal zinc and/or selenium phases independently on the electric parameters. For instance, in a layer deposited at a constant current density of 0.5 mA cm−2 on Ti from the F-type bath, diffraction from an elemental Zn phase is observed besides the occurrence of ZnSe (Fig. 1b). However, XRD shows that a stoichiometric ZnSe compound is obtained on Ni cathodes from solution G for pH 12 at room temperature (Fig. 3a). The diffraction from Ni substrate overlaps the (2 2 0) and (3 1 1) ZnSe reflections corresponding to 2θ = 45.3 and 53.7◦, re- spectively; thereby the formation of a very thin layer is obvi- ous. A chemical reaction at the substrate according to the mech- anism (ii) is most likely to occur for the employed baths. This effect is more obvious for the electrolytes D–J and less with the electrolytes K and L. For example in the case of a G- type bath, grains of pure ZnSe precipitating at the bottom of the cell are being formed (Fig. 3b). This product may arise not o adsorbed ( homogeneo tion; the lat reagents su or precipit Fig. 3. XRD at −1.5 V, fro NTA and 0.03 of 0.02 M SeS 10.5, at 85 ◦C up the precipi complex solutions of low selenosulfite anion concentrations (electrolytes A–C). Riveros et al. [15] report that electrodeposition from a selenosulfite-based solution on Ti and conductive glass cath- odes leads to the production of either very thin or amorphous ZnSe layers, as verified by EDX analysis, since the diffraction patterns reveal only the reflections of the substrate. However, on account of the results in the present work, the powder XRD data are sufficient to testify the occurrence of a rather stoi- chiometric ZnSe phase. Actually, a film thinning may occur during deposition due to the presence of a large quantity of sulfite ions enhancing the solubility of ZnSe [15]. It is important to remark that the selenosulfite method ap- pears to be more functional in systems similar like those described previously, yet containing other dissolved metal species in the liquid such as copper(II) or cadmium(II) ions. Specifically, the addition of a small amount of Cu2+ (5 M CuSO4) in the C-type deposition bath leads to the formation of a well-crystallized compound on the rotating Ti cathode (Fig. 4), which consists of a ZnCuSe phase with a composi- tion of about 42 Zn, 52 Se and 6 Cu (at.%); besides, supple- ment of Cd(II) in the bath E leads to the formation of an alloy containing about 51 Zn, 14 Se and 35 Cd (at.%), as EDX spectroscop field regard the produc roper ccordi holog flower differ sit, wh y nucl e Ti s attern . XRD t densit SO3, 0 nly from a reaction between deposited Zn and SeSO3)2− on the cathode, but also from a direct us interaction between the species in the solu- ter process is favoured by the addition of suitable ch as hydrazine. Finally, no ZnSe-containing films ates can be obtained from the excessive in zinc patterns of (a) a layer deposited on the smooth Ni electrode m a solution of 0.02 M SeSO32−, 0.02 M ZnSO4, 0.025 M M Na2SO3, pH 12, at 25 ◦C. (b) Solid residue from a solution O32−, 0.02 M ZnSO4, 0.028 M NTA and 0.08 M Na2SO3, pH . Hydrazine hydrate was added to the solution in order to speed tation. and p A morp cauli cally depo highl to th tion p Fig. 4 curren Na2Se y reveals. These results open up a very important ing the use of the selenosulfite alkaline method for tion of ternary systems with variable composition ties. ng to scanning electron microscopy (SEM), the y of the ZnCuSe film (Fig. 5a) manifests an open structure comprising a dendritic growth. A radi- ent mechanism operates in the case of the ZnCdSe ere the micrograph (Fig. 5b) shows a nodule-like, eated phase. The solid conglomerate is conformal ubstrate as can be observed from the reproduc- of the grain boundaries present on the roughened patterns of deposits prepared on the Ti electrodes at a constant y of 0.6 mA cm−2 from an alkaline (pH 9) bath of 5× 10−3 M .2 M ZnSO4, 0.2 M NTA and 0.1 M Na2SO3, at 85 ◦C. T. Kosanovic et al. / Materials Chemistry and Physics 90 (2005) 148–154 153 Fig. 5. SEM i 0.2 M ZnSO4 ammonia buff surface (als cathodic de duction of high rate of is substanti the particle herent laye position are to a nuclea substrate in mages of deposits prepared on rotating Ti electrodes at a constant current density o , 5× 10−3 M CuSO4, 0.2 M NTA and 0.1 M Na2SO3, pH 9, and (b) 0.025 M Na2Se er, pH 10, at 85 ◦C. Average composition (at.%) from EDX (a) 42 Zn, 52 Se, 6 Cu o [16]). The requirement of applying a sufficiently position potential/current density, ensuring the re- the constituent precursors, is associated with a nucleation since the crystallization overpotential ally surpassed, so that the growth and merging of s in larger aggregates that could give rise to a co- r is hindered. The highly cathodic potentials of de- necessary for the reduction of zinc, thus leading tion-dependent growth; a deposit departs from the fluence and develops as an aggregate, weakly co- herent laye mode (obs materials). eters towar growth is e Some p pulse platin E, K and L. cycle of a range. Dep f 0.6 mA cm−2 from a solution of (a) 5× 10−3 M Na2SeSO3, SO3, 0.025 M ZnSO4, 0.06 M NTA, 0.1 M Na2SO3 and 0.5 M and (b) 35 Zn, 51 Se, 14 Cd. r arising mainly by a three-dimensional nucleation erved with tetrahedrally structured non-metallic Therefore, the adaptation of the electrical param- ds the direction of the establishment of a slower ssential in the electrochemistry applied here. reliminary attempts to deposit ZnSe by using a g technique were carried out using the solutions The method involved the application of a repeated pair of cathodic potentials lying over a specific osits were obtained by using different duty cycles 154 T. Kosanovic et al. / Materials Chemistry and Physics 90 (2005) 148–154 for the applied potentials, in the range 10–70% for each value, the frequency being about 1 Hz for the more efficient exper- iments. The resulted films were amorphous in structure as indicated by the diffraction spectra; an example is shown in Fig. 1c. Note that at very negative potentials, reduction of Zn was competitive to ZnSe formation. All deposits formed on Ni and HF-acid-treated Ti elec- trodes were of poor adherence in contrast to the SnO2/glass and anodized Ti substrates that promoted stronger binding. The heterogeneous mechanism for the formation of ZnSe ap- pears to be more functional on the oxide (SnO2, TiOx) rather than the other substrates due to their increased specific sur- face of the formers and probable interaction with the reactants [4]. 5. Conclusions The ZnSe compound was electrochemically synthesized using a selenosulfite precursor in an alkaline environment. The produced electrodeposits were amorphous and loosely bound to the surface over a wide range of electrodeposition conditions, namely with various deposition potentials, work- ing substrates and different bath compositions; however, the frequently encountered problem of excessive elemental Se formed during the typical ZnSe electrodeposition from acidic solutions could be dealt with on an effective basis in most of the present experiments. The investigation showed the potential of a soft growth method of cess is rather complicated and vaguely defined but might be highly rewarding. A key point in this procedure is the selec- tion of an appropriate zinc complex, offering a potential for better growth control. References [1] K.K. Mishra, K. Rajeshwar, J. Electroanal. Chem. 273 (1989) 169. [2] C. Natarajan, M. Sharon, C. Le´vy-Cle´ment, M. Neumann-Spallart, Thin Solid Films 237 (1994) 118. [3] M. Bouroushian, T. Kosanovic, Z. Loizos, N. Spyrellis, J. Solid State Electrochem. 6 (2002) 272. 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Maurin, hin So stoichiometric ZnSe. The selenosulfite-based pro- T lid Films 381 (2001) 39. Soft growth of the ZnSe compound from alkaline selenosulfite solutions Introduction Experimental details Mechanistic approaches Selenosulfite solutions Metal complex Deposition mechanisms Growth aspects Results and discussion Conclusions References