ZnSe的电沉积

Available online at Electrochimica Acta53(2008)

6184–6190

Electrodeposition of ZnSe

Remigiusz Kowalik∗,1,Piotr˙Zabi´n ski,Krzysztof Fitzner

AGH University of Science and Technology,Faculty of Non-Ferrous Metals,Laboratory of Physical

Chemistry and Electrochemistry,Mickiewicz Avenue30,30-059Krakow,Poland

Received16August2007;received in revised form12November2007;accepted1December2007

Available online22January2008

Abstract

The conditions of the electrodeposition of a thinfilm of polycrystalline ZnSe phase on copper substrate from aqueous baths were studied.The electrochemical behavior of Zn2+and H2SeO3species was investigated using cyclic voltammetry.Thinfilms were deposited potentiostatically on copper substrate and the influence of deposition parameters such as deposition potential,H2SeO3and ZnSO4concentration,and temperature of bath on the crystallinity and on the chemical composition of thefilm is discussed.The ZnSe layers were characterized by X-ray diffraction,X-ray energy dispersive spectroscopy and scanning electron microscopy.

©2007Elsevier Ltd.All rights reserved.

Keywords:ZnSe;Semiconductors;Electrodeposition;Underpotential deposition;Cyclic voltammetry

1.Introduction

Zinc selenide is a well known II–VI semiconductor suit-able for the application in light emitting devices,and also is used for thinfilm solar cells as the window material[1–6] due to its wide energy band gap,i.e.2.7eV.There are many techniques used for ZnSe thinfilms production,i.e.vacuum deposition,chemical vapor deposition,metal-organic chemical vapor deposition,closed-spaced vapor transport or sputtering. Nevertheless,the electrodeposition process has some poten-tial advantages such as low-temperature operation.Moreover, it is convenient to use for a large area deposition and seems to be relatively low-cost technique.There are several reports on the electrodeposition of ZnSe from aqueous[7–12]and non-aqueous solutions[13],as well as from molten salt solutions [14].Zinc and selenium were also codeposited in order to syn-thesize ternary compounds like ZnCdSe[15,16]or ZnHgSe [17].

Wei and Rajeshwar used an electrochemicalflow cell depo-sition system to form ZnSe and CdSe structure[18].Theflow cell was used to alternate the deposition of these compounds,

∗Corresponding author.Tel.:+48126173611;fax:+48126173611.

E-mail address:rkowalik@.pl(R.Kowalik).

1ISE Member.creating a superlattice.This technique presents the possibility of deposition composition modulated structures.

Very promising proposition of ZnSe synthesis by Electro-chemical Atomic Layer Deposition(ECALE)applying also the flowing cell was proposed by Stickney and coworkers[19]and Foresti and coworkers[20].The ECALE method exploits surface limited electrochemical reactions,such as underpotential depo-sition(upd),to form alternate atomic layers of the elements making up compound layers of compounds.Each deposition cycle forms a monolayer of the compound,and the number of cycles determines how thick the deposit will be.

Electrochemical deposition of the elements from the aqueous solution begins after the electrode has been brought to a poten-tial more negative than the equilibrium potential characteristic of the chosen ion.If there are two different ions in the solution, one of them will always be relatively more noble.According to the Kr¨o ger’s theory it is possible to deposit simultaneously both elements without exceeding the equilibrium potential of one of them[21].This phenomenon is called underpotential deposition and should be observed during codeposition of zinc and sele-nium.The deposition potential of zinc is shifted towards positive values because of the contribution of the Gibbs free energy change of ZnSe formation[22].According to the Kr¨o ger’s model the process of the ZnSe synthesis can be achieved,when a large excess of zinc ions is present in the solution.Proper adjustment of the bath composition should lead to the formation

0013-4686/$–see front matter©2007Elsevier Ltd.All rights reserved. doi:10.1016/j.electacta.2007.12.009