JOURNAL OF APPLIED ELECTROCHEMISTRY 20 (1990) 868-873 An electrochemical route to GaSb thin films F. PAOLUCCI, G. MENGOLI, M. M. MUSIANI Istituto di Polarografia ed Elettrochimica Preparativa del CNR, Corso Stati Uniti, 4, 35020 Camin, Padova, Italy Received 20 October 1989; accepted 6 December 1989 An electrochemical method for the preparation of GaSb polycrystalline thin films is presented involving sequential deposition of Sb and Ga films (from an acid SbC13 solution and an alkaline GaC13 solution respectively) and a mild thermal annealing. The annealed deposits were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis (EDAX) and secondary ion mass spectrometry. An alternative approach based on the simultaneous deposition of Sb and Ga was unsuccessful. 1. Introduction Semiconducting III-V compounds are of great interest because of their use in the production of devices such as solar cells and sensors. When thin films of amorph- ous or polycrystalline semiconductors are needed, inexpensive electrochemical deposition methods may offer a viable alternative to the widely employed CVD, PACVD and sputtering techniques [1]. Many examples found in the literature concern the preparation of semiconducting chalcogenides, carried out either anodically or cathodically. Anodic synthesis of various sulphides was performed by oxidizing S2- on the appropriate anodes [2-5]. This method is a straightforward one, but control of the compound stoichiometry is rather difficult. The general rules governing alloy electrodeposition hold for the cathodic synthesis, in other words the process may be successful only when electrodeposition of the com- ponents occurs at comparable rates. The simultaneous discharge of two or more ions is particularly difficult to achieve when their standard potentials are much different. However, the proximity of the standard potentials is not an absolute requirement since many other factors play a major role: ion activity in solution, cathodic overpotential, use of complexing agents and/or surfactants, activity of the metals in the alloy [6]. Binary (e.g. CdSe [7], CdTe [8, 9], Snl+~Se [10]) and ternary chalcogenides (e.g. CuInSe2 [11]) were successfully prepared by codeposition. Various metal chalcogenides were also obtained by cathodic deposition from non-aqueous solutions containing a metal salt and molecular chalcogen [12, 13]. Less common are the examples of cathodically syn- thesized III-V semiconductors: InSb was obtained by codeposition from sulphate electrolytes [14, 15]; according to Sadana and Singh [15] complexation of the metal ions by citrate brings the reduction poten- tials of Sb and In close to each other, thus allowing codeposition in spite of large difference in the stan- dard potentials. GaSb was deposited from a non- aqueous (glycerol) medium [16, 17]. An entirely different electrochemical approach to the synthesis of semiconducting alloys involves elec- trodeposition of precisely controlled amounts of the individual components as successive layers followed by thermal annealing which induces diffusion and reaction to the desired compound. CuInSe2 was prepared by this method or by annealing a two-layer deposit of Cu and In in a H2Se atmosphere [18]. CuInS 2 was also prepared in a similar way, the anneal- ing being performed in an environment where H2S was electrochemically generated [19]. The multilayer approach is claimed to be fairly general. In the present paper we describe an investigation aimed at synthesizing thin films of GaSb by exploring the two alternative electrochemical strategies of simul- taneous and sequential deposition of Sb and Ga. The electrodeposition of both pure metals (for Sb see [17, 20], for Ga [21-24]) and their anodic dissolution (for Sb see [25, 26], for Ga [27-30]) are well documented in the literature. 2. Experimental details 2.1. Substrates and electrodes Nickel-plated Cu sheets were chosen as substrates for the preparation of GaSb films. The copper sheets (2-3cm 2) were carefully degreased and rinsed with acetone followed by air-drying. Then, Ni films approxi- mately 5 #m thick were galvanostatically deposited from a Watts-type bath of the following composition: 1.1M NiSO4, 0.5M NH4C1, 0.5M H3BO 3 and NH4OH (pH5.9). For some experiments, nickel (99.99%) and antimony (99.998%, Johnson Matthey) discs mounted on brass and held in a tightly fitting PTFE sheath were used as either stationary or rotating working electrodes. A carbon paste GaSb electrode was prepared by intimately mixing finely powdered commercial GaSb (1%), pyrolythic graphite powder and silicon oil (550, Carlo Erba) as the binder liquid and filling a glass tube with that paste [31]. 868 0021-891X/90 $03.00 + .12 9 1990Chapman and Hall Ltd.