ERDA analysis of ZnS x (OH) y thin films obtained by chemical bath deposition
- PDF / 48,466 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 27 Downloads / 224 Views
ERDA analysis of ZnSx(OH)y thin films obtained by chemical bath deposition Sven Neve, Wolfgang Bohne, Jörg Röhrich, Roland Scheer Hahn-Meitner-Institut Berlin GmbH, Glienicker Str. 100, D-14109 Berlin, Germany, phone/fax: ++49-30-8062-2789, email: [email protected] ABSTRACT Thin films of Zn-compounds grown in a chemical bath have been studied by Elastic Recoil Detection Analysis (ERDA). The bath contained zinc acetate, thiourea and complexing agents such as ammonia and hydrazine. Large amounts of hydrogen and oxygen are detected within all samples. A strong effect of the pH of the solution is revealed: At high pH (>11.5) mainly ZnS growth takes place, while at lower pH Zn(OH)2 is the dominant product. Hence the pH of the solution can be used to adjust the film stoichiometry. Deposition of Zn-compound films is possible without ammonia in the solution while presence of hydroxide ions and hydrazine species is necessary. It is proposed that film formation takes place via a complex combining hydrazine and hydroxide ligands. INTRODUCTION Thin films of zinc sulfide (ZnS) are of considerable interest in view of their application in optoelectronic devices [1,2]. Among several preparation methods for ZnS films, chemical bath deposition (CBD) is particular suitable for solar cells due to its capability of homogeneous coverage. First CBD-ZnS thin films were grown using ammonia (NH3) as well as triethanolamine (N(CH2CH2OH)3) as complexing agents [3]. In that case, the growth rate was low. Using hydrazine (N2H4) instead of triethanolamine as a second ligand, considerable growth acceleration has been observed [4,5]. The CBD process allows the formation of compounds of low solubility whereby the cation concentration is controlled by complexing agents (eq. 1) and anions are released by slow decomposition of a chalcogenide source (eq. 2) [6,7]. Mx+ + nLy- = [MLn]z+
(1)
SC(NH2)2 + 2OH- = S2- + CH2N2 + 2H2O
(2)
The formation of ZnS can be formulated by a reaction of the complex with sulfide ions [4]. [ZnLn]z+ + S2- = ZnS + nLy-
(3)
The intermediate Zn-complex has not been identified yet, a task which certainly is difficult on an analytical level. Ammonia or hydrazine complexes such as [Zn(NH3)3]2+ , [Zn(NH3)4]2+ or [Zn(N2H4)4]2+ are discussed [8,9,4]. Also ternary complexes such as [Zn(N2H4)2(NH3)2]2+ or Zn(NH3)2(OH)2 have been proposed [10,11]. A problem refers to the product of the chemical bath deposition. While the formation of stoichiometric ZnS films was reported [4], it has been pointed out that oxygen is contained within the films [5]. In the present work, we use elastic H5.3.1
recoil detection analysis (ERDA) for measuring film composition and film thickness. The ERDA technique is a powerful tool for the characterization of all relevant elements on a quantitative basis. In principle, ERDA has depth resolution capability and allows the estimation of the sample roughness. In the presented experiments, we varied the concentrations of NH3, N2H4, and SC(NH2)2. In some experiments we replaced NH3 to different extents by potassiu
Data Loading...
